From: Aaron Schulz Date: Fri, 2 Aug 2019 22:01:53 +0000 (-0400) Subject: Move WANObjectCache to wancache/ instead of WinCache X-Git-Tag: 1.34.0-rc.0~799 X-Git-Url: http://git.cyclocoop.org/%7B%24admin_url%7Dcompta/comptes/journal.php?a=commitdiff_plain;h=0bee81df816e00394400574d9bc95bde55bfe092;p=lhc%2Fweb%2Fwiklou.git Move WANObjectCache to wancache/ instead of WinCache Follow up 6ca3de5fa0. Change-Id: I7021dfe5c900f810ab3b6dc701a04e2c3e1c4c66 --- diff --git a/autoload.php b/autoload.php index 65b4e233d6..0208a6d783 100644 --- a/autoload.php +++ b/autoload.php @@ -1593,7 +1593,7 @@ $wgAutoloadLocalClasses = [ 'VirtualRESTService' => __DIR__ . '/includes/libs/virtualrest/VirtualRESTService.php', 'VirtualRESTServiceClient' => __DIR__ . '/includes/libs/virtualrest/VirtualRESTServiceClient.php', 'WANCacheReapUpdate' => __DIR__ . '/includes/deferred/WANCacheReapUpdate.php', - 'WANObjectCache' => __DIR__ . '/includes/libs/objectcache/WANObjectCache.php', + 'WANObjectCache' => __DIR__ . '/includes/libs/objectcache/wancache/WANObjectCache.php', 'WANObjectCacheReaper' => __DIR__ . '/includes/libs/objectcache/wancache/WANObjectCacheReaper.php', 'WantedCategoriesPage' => __DIR__ . '/includes/specials/SpecialWantedcategories.php', 'WantedFilesPage' => __DIR__ . '/includes/specials/SpecialWantedfiles.php', @@ -1706,7 +1706,7 @@ $wgAutoloadLocalClasses = [ 'WikitextContent' => __DIR__ . '/includes/content/WikitextContent.php', 'WikitextContentHandler' => __DIR__ . '/includes/content/WikitextContentHandler.php', 'WikitextLogFormatter' => __DIR__ . '/includes/logging/WikitextLogFormatter.php', - 'WinCacheBagOStuff' => __DIR__ . '/includes/libs/objectcache/wancache/WinCacheBagOStuff.php', + 'WinCacheBagOStuff' => __DIR__ . '/includes/libs/objectcache/WinCacheBagOStuff.php', 'WithoutInterwikiPage' => __DIR__ . '/includes/specials/SpecialWithoutinterwiki.php', 'WordLevelDiff' => __DIR__ . '/includes/diff/WordLevelDiff.php', 'WrapOldPasswords' => __DIR__ . '/maintenance/wrapOldPasswords.php', diff --git a/includes/libs/objectcache/WANObjectCache.php b/includes/libs/objectcache/WANObjectCache.php deleted file mode 100644 index 1852685d6c..0000000000 --- a/includes/libs/objectcache/WANObjectCache.php +++ /dev/null @@ -1,2633 +0,0 @@ -= 0 due to clock skew */ - private static $TINY_NEGATIVE = -0.000001; - /** @var float Tiny positive float to use when using "minTime" to assert an inequality */ - private static $TINY_POSTIVE = 0.000001; - - /** @var int Milliseconds of key fetch/validate/regenerate delay prone to set() stampedes */ - private static $SET_DELAY_HIGH_MS = 50; - /** @var int Min millisecond set() backoff during hold-off (far less than INTERIM_KEY_TTL) */ - private static $RECENT_SET_LOW_MS = 50; - /** @var int Max millisecond set() backoff during hold-off (far less than INTERIM_KEY_TTL) */ - private static $RECENT_SET_HIGH_MS = 100; - - /** @var int Consider value generation slow if it takes more than this many seconds */ - private static $GENERATION_SLOW_SEC = 3; - - /** @var int Key to the tombstone entry timestamp */ - private static $PURGE_TIME = 0; - /** @var int Key to the tombstone entry hold-off TTL */ - private static $PURGE_HOLDOFF = 1; - - /** @var int Cache format version number */ - private static $VERSION = 1; - - /** @var int Key to WAN cache version number */ - private static $FLD_FORMAT_VERSION = 0; - /** @var int Key to the cached value */ - private static $FLD_VALUE = 1; - /** @var int Key to the original TTL */ - private static $FLD_TTL = 2; - /** @var int Key to the cache timestamp */ - private static $FLD_TIME = 3; - /** @var int Key to the flags bit field (reserved number) */ - private static /** @noinspection PhpUnusedPrivateFieldInspection */ $FLD_FLAGS = 4; - /** @var int Key to collection cache version number */ - private static $FLD_VALUE_VERSION = 5; - /** @var int Key to how long it took to generate the value */ - private static $FLD_GENERATION_TIME = 6; - - private static $VALUE_KEY_PREFIX = 'WANCache:v:'; - private static $INTERIM_KEY_PREFIX = 'WANCache:i:'; - private static $TIME_KEY_PREFIX = 'WANCache:t:'; - private static $MUTEX_KEY_PREFIX = 'WANCache:m:'; - private static $COOLOFF_KEY_PREFIX = 'WANCache:c:'; - - private static $PURGE_VAL_PREFIX = 'PURGED:'; - - /** - * @param array $params - * - cache : BagOStuff object for a persistent cache - * - logger : LoggerInterface object - * - stats : StatsdDataFactoryInterface object - * - asyncHandler : A function that takes a callback and runs it later. If supplied, - * whenever a preemptive refresh would be triggered in getWithSetCallback(), the - * current cache value is still used instead. However, the async-handler function - * receives a WAN cache callback that, when run, will execute the value generation - * callback supplied by the getWithSetCallback() caller. The result will be saved - * as normal. The handler is expected to call the WAN cache callback at an opportune - * time (e.g. HTTP post-send), though generally within a few 100ms. [optional] - * - region: the current physical region. This is required when using mcrouter as the - * backing store proxy. [optional] - * - cluster: name of the cache cluster used by this WAN cache. The name must be the - * same in all datacenters; the ("region","cluster") tuple is what distinguishes - * the counterpart cache clusters among all the datacenter. The contents of - * https://github.com/facebook/mcrouter/wiki/Config-Files give background on this. - * This is required when using mcrouter as the backing store proxy. [optional] - * - mcrouterAware: set as true if mcrouter is the backing store proxy and mcrouter - * is configured to interpret /// key prefixes as routes. This - * requires that "region" and "cluster" are both set above. [optional] - * - epoch: lowest UNIX timestamp a value/tombstone must have to be valid. [optional] - * - secret: stable secret used for hashing long strings into key components. [optional] - */ - public function __construct( array $params ) { - $this->cache = $params['cache']; - $this->region = $params['region'] ?? 'main'; - $this->cluster = $params['cluster'] ?? 'wan-main'; - $this->mcrouterAware = !empty( $params['mcrouterAware'] ); - $this->epoch = $params['epoch'] ?? 0; - $this->secret = $params['secret'] ?? (string)$this->epoch; - - $this->setLogger( $params['logger'] ?? new NullLogger() ); - $this->stats = $params['stats'] ?? new NullStatsdDataFactory(); - $this->asyncHandler = $params['asyncHandler'] ?? null; - } - - /** - * @param LoggerInterface $logger - */ - public function setLogger( LoggerInterface $logger ) { - $this->logger = $logger; - } - - /** - * Get an instance that wraps EmptyBagOStuff - * - * @return WANObjectCache - */ - public static function newEmpty() { - return new static( [ 'cache' => new EmptyBagOStuff() ] ); - } - - /** - * Fetch the value of a key from cache - * - * If supplied, $curTTL is set to the remaining TTL (current time left): - * - a) INF; if $key exists, has no TTL, and is not invalidated by $checkKeys - * - b) float (>=0); if $key exists, has a TTL, and is not invalidated by $checkKeys - * - c) float (<0); if $key is tombstoned, stale, or existing but invalidated by $checkKeys - * - d) null; if $key does not exist and is not tombstoned - * - * If a key is tombstoned, $curTTL will reflect the time since delete(). - * - * The timestamp of $key will be checked against the last-purge timestamp - * of each of $checkKeys. Those $checkKeys not in cache will have the last-purge - * initialized to the current timestamp. If any of $checkKeys have a timestamp - * greater than that of $key, then $curTTL will reflect how long ago $key - * became invalid. Callers can use $curTTL to know when the value is stale. - * The $checkKeys parameter allow mass invalidations by updating a single key: - * - a) Each "check" key represents "last purged" of some source data - * - b) Callers pass in relevant "check" keys as $checkKeys in get() - * - c) When the source data that "check" keys represent changes, - * the touchCheckKey() method is called on them - * - * Source data entities might exists in a DB that uses snapshot isolation - * (e.g. the default REPEATABLE-READ in innoDB). Even for mutable data, that - * isolation can largely be maintained by doing the following: - * - a) Calling delete() on entity change *and* creation, before DB commit - * - b) Keeping transaction duration shorter than the delete() hold-off TTL - * - c) Disabling interim key caching via useInterimHoldOffCaching() before get() calls - * - * However, pre-snapshot values might still be seen if an update was made - * in a remote datacenter but the purge from delete() didn't relay yet. - * - * Consider using getWithSetCallback() instead of get() and set() cycles. - * That method has cache slam avoiding features for hot/expensive keys. - * - * Pass $info as WANObjectCache::PASS_BY_REF to transform it into a cache key metadata map. - * This map includes the following metadata: - * - asOf: UNIX timestamp of the value or null if the key is nonexistant - * - tombAsOf: UNIX timestamp of the tombstone or null if the key is not tombstoned - * - lastCKPurge: UNIX timestamp of the highest check key or null if none provided - * - version: cached value version number or null if the key is nonexistant - * - * Otherwise, $info will transform into the cached value timestamp. - * - * @param string $key Cache key made from makeKey() or makeGlobalKey() - * @param mixed|null &$curTTL Approximate TTL left on the key if present/tombstoned [returned] - * @param string[] $checkKeys The "check" keys used to validate the value - * @param mixed|null &$info Key info if WANObjectCache::PASS_BY_REF [returned] - * @return mixed Value of cache key or false on failure - */ - final public function get( - $key, &$curTTL = null, array $checkKeys = [], &$info = null - ) { - $curTTLs = self::PASS_BY_REF; - $infoByKey = self::PASS_BY_REF; - $values = $this->getMulti( [ $key ], $curTTLs, $checkKeys, $infoByKey ); - $curTTL = $curTTLs[$key] ?? null; - if ( $info === self::PASS_BY_REF ) { - $info = [ - 'asOf' => $infoByKey[$key]['asOf'] ?? null, - 'tombAsOf' => $infoByKey[$key]['tombAsOf'] ?? null, - 'lastCKPurge' => $infoByKey[$key]['lastCKPurge'] ?? null, - 'version' => $infoByKey[$key]['version'] ?? null - ]; - } else { - $info = $infoByKey[$key]['asOf'] ?? null; // b/c - } - - return $values[$key] ?? false; - } - - /** - * Fetch the value of several keys from cache - * - * Pass $info as WANObjectCache::PASS_BY_REF to transform it into a map of cache keys - * to cache key metadata maps, each having the same style as those of WANObjectCache::get(). - * All the cache keys listed in $keys will have an entry. - * - * Othwerwise, $info will transform into a map of (cache key => cached value timestamp). - * Only the cache keys listed in $keys that exists or are tombstoned will have an entry. - * - * $checkKeys holds the "check" keys used to validate values of applicable keys. The integer - * indexes hold "check" keys that apply to all of $keys while the string indexes hold "check" - * keys that only apply to the cache key with that name. - * - * @see WANObjectCache::get() - * - * @param string[] $keys List of cache keys made from makeKey() or makeGlobalKey() - * @param mixed|null &$curTTLs Map of (key => TTL left) for existing/tombstoned keys [returned] - * @param string[]|string[][] $checkKeys Map of (integer or cache key => "check" key(s)) - * @param mixed|null &$info Map of (key => info) if WANObjectCache::PASS_BY_REF [returned] - * @return mixed[] Map of (key => value) for existing values; order of $keys is preserved - */ - final public function getMulti( - array $keys, - &$curTTLs = [], - array $checkKeys = [], - &$info = null - ) { - $result = []; - $curTTLs = []; - $infoByKey = []; - - $vPrefixLen = strlen( self::$VALUE_KEY_PREFIX ); - $valueKeys = self::prefixCacheKeys( $keys, self::$VALUE_KEY_PREFIX ); - - $checkKeysForAll = []; - $checkKeysByKey = []; - $checkKeysFlat = []; - foreach ( $checkKeys as $i => $checkKeyGroup ) { - $prefixed = self::prefixCacheKeys( (array)$checkKeyGroup, self::$TIME_KEY_PREFIX ); - $checkKeysFlat = array_merge( $checkKeysFlat, $prefixed ); - // Are these check keys for a specific cache key, or for all keys being fetched? - if ( is_int( $i ) ) { - $checkKeysForAll = array_merge( $checkKeysForAll, $prefixed ); - } else { - $checkKeysByKey[$i] = $prefixed; - } - } - - // Fetch all of the raw values - $keysGet = array_merge( $valueKeys, $checkKeysFlat ); - if ( $this->warmupCache ) { - $wrappedValues = array_intersect_key( $this->warmupCache, array_flip( $keysGet ) ); - $keysGet = array_diff( $keysGet, array_keys( $wrappedValues ) ); // keys left to fetch - $this->warmupKeyMisses += count( $keysGet ); - } else { - $wrappedValues = []; - } - if ( $keysGet ) { - $wrappedValues += $this->cache->getMulti( $keysGet ); - } - // Time used to compare/init "check" keys (derived after getMulti() to be pessimistic) - $now = $this->getCurrentTime(); - - // Collect timestamps from all "check" keys - $purgeValuesForAll = $this->processCheckKeys( $checkKeysForAll, $wrappedValues, $now ); - $purgeValuesByKey = []; - foreach ( $checkKeysByKey as $cacheKey => $checks ) { - $purgeValuesByKey[$cacheKey] = - $this->processCheckKeys( $checks, $wrappedValues, $now ); - } - - // Get the main cache value for each key and validate them - foreach ( $valueKeys as $vKey ) { - $key = substr( $vKey, $vPrefixLen ); // unprefix - list( $value, $keyInfo ) = $this->unwrap( $wrappedValues[$vKey] ?? false, $now ); - // Force dependent keys to be seen as stale for a while after purging - // to reduce race conditions involving stale data getting cached - $purgeValues = $purgeValuesForAll; - if ( isset( $purgeValuesByKey[$key] ) ) { - $purgeValues = array_merge( $purgeValues, $purgeValuesByKey[$key] ); - } - - $lastCKPurge = null; // timestamp of the highest check key - foreach ( $purgeValues as $purge ) { - $lastCKPurge = max( $purge[self::$PURGE_TIME], $lastCKPurge ); - $safeTimestamp = $purge[self::$PURGE_TIME] + $purge[self::$PURGE_HOLDOFF]; - if ( $value !== false && $safeTimestamp >= $keyInfo['asOf'] ) { - // How long ago this value was invalidated by *this* check key - $ago = min( $purge[self::$PURGE_TIME] - $now, self::$TINY_NEGATIVE ); - // How long ago this value was invalidated by *any* known check key - $keyInfo['curTTL'] = min( $keyInfo['curTTL'], $ago ); - } - } - $keyInfo[ 'lastCKPurge'] = $lastCKPurge; - - if ( $value !== false ) { - $result[$key] = $value; - } - if ( $keyInfo['curTTL'] !== null ) { - $curTTLs[$key] = $keyInfo['curTTL']; - } - - $infoByKey[$key] = ( $info === self::PASS_BY_REF ) - ? $keyInfo - : $keyInfo['asOf']; // b/c - } - - $info = $infoByKey; - - return $result; - } - - /** - * @since 1.27 - * @param string[] $timeKeys List of prefixed time check keys - * @param mixed[] $wrappedValues - * @param float $now - * @return array[] List of purge value arrays - */ - private function processCheckKeys( array $timeKeys, array $wrappedValues, $now ) { - $purgeValues = []; - foreach ( $timeKeys as $timeKey ) { - $purge = isset( $wrappedValues[$timeKey] ) - ? $this->parsePurgeValue( $wrappedValues[$timeKey] ) - : false; - if ( $purge === false ) { - // Key is not set or malformed; regenerate - $newVal = $this->makePurgeValue( $now, self::HOLDOFF_TTL ); - $this->cache->add( $timeKey, $newVal, self::$CHECK_KEY_TTL ); - $purge = $this->parsePurgeValue( $newVal ); - } - $purgeValues[] = $purge; - } - return $purgeValues; - } - - /** - * Set the value of a key in cache - * - * Simply calling this method when source data changes is not valid because - * the changes do not replicate to the other WAN sites. In that case, delete() - * should be used instead. This method is intended for use on cache misses. - * - * If the data was read from a snapshot-isolated transactions (e.g. the default - * REPEATABLE-READ in innoDB), use 'since' to avoid the following race condition: - * - a) T1 starts - * - b) T2 updates a row, calls delete(), and commits - * - c) The HOLDOFF_TTL passes, expiring the delete() tombstone - * - d) T1 reads the row and calls set() due to a cache miss - * - e) Stale value is stuck in cache - * - * Setting 'lag' and 'since' help avoids keys getting stuck in stale states. - * - * Be aware that this does not update the process cache for getWithSetCallback() - * callers. Keys accessed via that method are not generally meant to also be set - * using this primitive method. - * - * Do not use this method on versioned keys accessed via getWithSetCallback(). - * - * Example usage: - * @code - * $dbr = wfGetDB( DB_REPLICA ); - * $setOpts = Database::getCacheSetOptions( $dbr ); - * // Fetch the row from the DB - * $row = $dbr->selectRow( ... ); - * $key = $cache->makeKey( 'building', $buildingId ); - * $cache->set( $key, $row, $cache::TTL_DAY, $setOpts ); - * @endcode - * - * @param string $key Cache key - * @param mixed $value - * @param int $ttl Seconds to live. Special values are: - * - WANObjectCache::TTL_INDEFINITE: Cache forever (default) - * - WANObjectCache::TTL_UNCACHEABLE: Do not cache (if the key exists, it is not deleted) - * @param array $opts Options map: - * - lag: Seconds of replica DB lag. Typically, this is either the replica DB lag - * before the data was read or, if applicable, the replica DB lag before - * the snapshot-isolated transaction the data was read from started. - * Use false to indicate that replication is not running. - * Default: 0 seconds - * - since: UNIX timestamp of the data in $value. Typically, this is either - * the current time the data was read or (if applicable) the time when - * the snapshot-isolated transaction the data was read from started. - * Default: 0 seconds - * - pending: Whether this data is possibly from an uncommitted write transaction. - * Generally, other threads should not see values from the future and - * they certainly should not see ones that ended up getting rolled back. - * Default: false - * - lockTSE: If excessive replication/snapshot lag is detected, then store the value - * with this TTL and flag it as stale. This is only useful if the reads for this key - * use getWithSetCallback() with "lockTSE" set. Note that if "staleTTL" is set - * then it will still add on to this TTL in the excessive lag scenario. - * Default: WANObjectCache::TSE_NONE - * - staleTTL: Seconds to keep the key around if it is stale. The get()/getMulti() - * methods return such stale values with a $curTTL of 0, and getWithSetCallback() - * will call the regeneration callback in such cases, passing in the old value - * and its as-of time to the callback. This is useful if adaptiveTTL() is used - * on the old value's as-of time when it is verified as still being correct. - * Default: WANObjectCache::STALE_TTL_NONE - * - creating: Optimize for the case where the key does not already exist. - * Default: false - * - version: Integer version number signifiying the format of the value. - * Default: null - * - walltime: How long the value took to generate in seconds. Default: 0.0 - * @note Options added in 1.28: staleTTL - * @note Options added in 1.33: creating - * @note Options added in 1.34: version, walltime - * @return bool Success - */ - final public function set( $key, $value, $ttl = self::TTL_INDEFINITE, array $opts = [] ) { - $now = $this->getCurrentTime(); - $lag = $opts['lag'] ?? 0; - $age = isset( $opts['since'] ) ? max( 0, $now - $opts['since'] ) : 0; - $pending = $opts['pending'] ?? false; - $lockTSE = $opts['lockTSE'] ?? self::TSE_NONE; - $staleTTL = $opts['staleTTL'] ?? self::STALE_TTL_NONE; - $creating = $opts['creating'] ?? false; - $version = $opts['version'] ?? null; - $walltime = $opts['walltime'] ?? 0.0; - - if ( $ttl < 0 ) { - return true; - } - - // Do not cache potentially uncommitted data as it might get rolled back - if ( $pending ) { - $this->logger->info( - 'Rejected set() for {cachekey} due to pending writes.', - [ 'cachekey' => $key ] - ); - - return true; // no-op the write for being unsafe - } - - $logicalTTL = null; // logical TTL override - // Check if there's a risk of writing stale data after the purge tombstone expired - if ( $lag === false || ( $lag + $age ) > self::MAX_READ_LAG ) { - // Case A: any long-running transaction - if ( $age > self::MAX_READ_LAG ) { - if ( $lockTSE >= 0 ) { - // Store value as *almost* stale to avoid cache and mutex stampedes - $logicalTTL = self::TTL_SECOND; - $this->logger->info( - 'Lowered set() TTL for {cachekey} due to snapshot lag.', - [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] - ); - } else { - $this->logger->info( - 'Rejected set() for {cachekey} due to snapshot lag.', - [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] - ); - - return true; // no-op the write for being unsafe - } - // Case B: high replication lag; lower TTL instead of ignoring all set()s - } elseif ( $lag === false || $lag > self::MAX_READ_LAG ) { - if ( $lockTSE >= 0 ) { - $logicalTTL = min( $ttl ?: INF, self::TTL_LAGGED ); - } else { - $ttl = min( $ttl ?: INF, self::TTL_LAGGED ); - } - $this->logger->warning( - 'Lowered set() TTL for {cachekey} due to replication lag.', - [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] - ); - // Case C: medium length request with medium replication lag - } elseif ( $lockTSE >= 0 ) { - // Store value as *almost* stale to avoid cache and mutex stampedes - $logicalTTL = self::TTL_SECOND; - $this->logger->info( - 'Lowered set() TTL for {cachekey} due to high read lag.', - [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] - ); - } else { - $this->logger->info( - 'Rejected set() for {cachekey} due to high read lag.', - [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] - ); - - return true; // no-op the write for being unsafe - } - } - - // Wrap that value with time/TTL/version metadata - $wrapped = $this->wrap( $value, $logicalTTL ?: $ttl, $version, $now, $walltime ); - $storeTTL = $ttl + $staleTTL; - - if ( $creating ) { - $ok = $this->cache->add( self::$VALUE_KEY_PREFIX . $key, $wrapped, $storeTTL ); - } else { - $ok = $this->cache->merge( - self::$VALUE_KEY_PREFIX . $key, - function ( $cache, $key, $cWrapped ) use ( $wrapped ) { - // A string value means that it is a tombstone; do nothing in that case - return ( is_string( $cWrapped ) ) ? false : $wrapped; - }, - $storeTTL, - 1 // 1 attempt - ); - } - - return $ok; - } - - /** - * Purge a key from all datacenters - * - * This should only be called when the underlying data (being cached) - * changes in a significant way. This deletes the key and starts a hold-off - * period where the key cannot be written to for a few seconds (HOLDOFF_TTL). - * This is done to avoid the following race condition: - * - a) Some DB data changes and delete() is called on a corresponding key - * - b) A request refills the key with a stale value from a lagged DB - * - c) The stale value is stuck there until the key is expired/evicted - * - * This is implemented by storing a special "tombstone" value at the cache - * key that this class recognizes; get() calls will return false for the key - * and any set() calls will refuse to replace tombstone values at the key. - * For this to always avoid stale value writes, the following must hold: - * - a) Replication lag is bounded to being less than HOLDOFF_TTL; or - * - b) If lag is higher, the DB will have gone into read-only mode already - * - * Note that set() can also be lag-aware and lower the TTL if it's high. - * - * Be aware that this does not clear the process cache. Even if it did, callbacks - * used by getWithSetCallback() might still return stale data in the case of either - * uncommitted or not-yet-replicated changes (callback generally use replica DBs). - * - * When using potentially long-running ACID transactions, a good pattern is - * to use a pre-commit hook to issue the delete. This means that immediately - * after commit, callers will see the tombstone in cache upon purge relay. - * It also avoids the following race condition: - * - a) T1 begins, changes a row, and calls delete() - * - b) The HOLDOFF_TTL passes, expiring the delete() tombstone - * - c) T2 starts, reads the row and calls set() due to a cache miss - * - d) T1 finally commits - * - e) Stale value is stuck in cache - * - * Example usage: - * @code - * $dbw->startAtomic( __METHOD__ ); // start of request - * ... ... - * // Update the row in the DB - * $dbw->update( ... ); - * $key = $cache->makeKey( 'homes', $homeId ); - * // Purge the corresponding cache entry just before committing - * $dbw->onTransactionPreCommitOrIdle( function() use ( $cache, $key ) { - * $cache->delete( $key ); - * } ); - * ... ... - * $dbw->endAtomic( __METHOD__ ); // end of request - * @endcode - * - * The $ttl parameter can be used when purging values that have not actually changed - * recently. For example, a cleanup script to purge cache entries does not really need - * a hold-off period, so it can use HOLDOFF_TTL_NONE. Likewise for user-requested purge. - * Note that $ttl limits the effective range of 'lockTSE' for getWithSetCallback(). - * - * If called twice on the same key, then the last hold-off TTL takes precedence. For - * idempotence, the $ttl should not vary for different delete() calls on the same key. - * - * @param string $key Cache key - * @param int $ttl Tombstone TTL; Default: WANObjectCache::HOLDOFF_TTL - * @return bool True if the item was purged or not found, false on failure - */ - final public function delete( $key, $ttl = self::HOLDOFF_TTL ) { - if ( $ttl <= 0 ) { - // Publish the purge to all datacenters - $ok = $this->relayDelete( self::$VALUE_KEY_PREFIX . $key ); - } else { - // Publish the purge to all datacenters - $ok = $this->relayPurge( self::$VALUE_KEY_PREFIX . $key, $ttl, self::HOLDOFF_TTL_NONE ); - } - - $kClass = $this->determineKeyClassForStats( $key ); - $this->stats->increment( "wanobjectcache.$kClass.delete." . ( $ok ? 'ok' : 'error' ) ); - - return $ok; - } - - /** - * Fetch the value of a timestamp "check" key - * - * The key will be *initialized* to the current time if not set, - * so only call this method if this behavior is actually desired - * - * The timestamp can be used to check whether a cached value is valid. - * Callers should not assume that this returns the same timestamp in - * all datacenters due to relay delays. - * - * The level of staleness can roughly be estimated from this key, but - * if the key was evicted from cache, such calculations may show the - * time since expiry as ~0 seconds. - * - * Note that "check" keys won't collide with other regular keys. - * - * @param string $key - * @return float UNIX timestamp - */ - final public function getCheckKeyTime( $key ) { - return $this->getMultiCheckKeyTime( [ $key ] )[$key]; - } - - /** - * Fetch the values of each timestamp "check" key - * - * This works like getCheckKeyTime() except it takes a list of keys - * and returns a map of timestamps instead of just that of one key - * - * This might be useful if both: - * - a) a class of entities each depend on hundreds of other entities - * - b) these other entities are depended upon by millions of entities - * - * The later entities can each use a "check" key to invalidate their dependee entities. - * However, it is expensive for the former entities to verify against all of the relevant - * "check" keys during each getWithSetCallback() call. A less expensive approach is to do - * these verifications only after a "time-till-verify" (TTV) has passed. This is a middle - * ground between using blind TTLs and using constant verification. The adaptiveTTL() method - * can be used to dynamically adjust the TTV. Also, the initial TTV can make use of the - * last-modified times of the dependant entities (either from the DB or the "check" keys). - * - * Example usage: - * @code - * $value = $cache->getWithSetCallback( - * $cache->makeGlobalKey( 'wikibase-item', $id ), - * self::INITIAL_TTV, // initial time-till-verify - * function ( $oldValue, &$ttv, &$setOpts, $oldAsOf ) use ( $checkKeys, $cache ) { - * $now = microtime( true ); - * // Use $oldValue if it passes max ultimate age and "check" key comparisons - * if ( $oldValue && - * $oldAsOf > max( $cache->getMultiCheckKeyTime( $checkKeys ) ) && - * ( $now - $oldValue['ctime'] ) <= self::MAX_CACHE_AGE - * ) { - * // Increase time-till-verify by 50% of last time to reduce overhead - * $ttv = $cache->adaptiveTTL( $oldAsOf, self::MAX_TTV, self::MIN_TTV, 1.5 ); - * // Unlike $oldAsOf, "ctime" is the ultimate age of the cached data - * return $oldValue; - * } - * - * $mtimes = []; // dependency last-modified times; passed by reference - * $value = [ 'data' => $this->fetchEntityData( $mtimes ), 'ctime' => $now ]; - * // Guess time-till-change among the dependencies, e.g. 1/(total change rate) - * $ttc = 1 / array_sum( array_map( - * function ( $mtime ) use ( $now ) { - * return 1 / ( $mtime ? ( $now - $mtime ) : 900 ); - * }, - * $mtimes - * ) ); - * // The time-to-verify should not be overly pessimistic nor optimistic - * $ttv = min( max( $ttc, self::MIN_TTV ), self::MAX_TTV ); - * - * return $value; - * }, - * [ 'staleTTL' => $cache::TTL_DAY ] // keep around to verify and re-save - * ); - * @endcode - * - * @see WANObjectCache::getCheckKeyTime() - * @see WANObjectCache::getWithSetCallback() - * - * @param string[] $keys - * @return float[] Map of (key => UNIX timestamp) - * @since 1.31 - */ - final public function getMultiCheckKeyTime( array $keys ) { - $rawKeys = []; - foreach ( $keys as $key ) { - $rawKeys[$key] = self::$TIME_KEY_PREFIX . $key; - } - - $rawValues = $this->cache->getMulti( $rawKeys ); - $rawValues += array_fill_keys( $rawKeys, false ); - - $times = []; - foreach ( $rawKeys as $key => $rawKey ) { - $purge = $this->parsePurgeValue( $rawValues[$rawKey] ); - if ( $purge !== false ) { - $time = $purge[self::$PURGE_TIME]; - } else { - // Casting assures identical floats for the next getCheckKeyTime() calls - $now = (string)$this->getCurrentTime(); - $this->cache->add( - $rawKey, - $this->makePurgeValue( $now, self::HOLDOFF_TTL ), - self::$CHECK_KEY_TTL - ); - $time = (float)$now; - } - - $times[$key] = $time; - } - - return $times; - } - - /** - * Purge a "check" key from all datacenters, invalidating keys that use it - * - * This should only be called when the underlying data (being cached) - * changes in a significant way, and it is impractical to call delete() - * on all keys that should be changed. When get() is called on those - * keys, the relevant "check" keys must be supplied for this to work. - * - * The "check" key essentially represents a last-modified time of an entity. - * When the key is touched, the timestamp will be updated to the current time. - * Keys using the "check" key via get(), getMulti(), or getWithSetCallback() will - * be invalidated. This approach is useful if many keys depend on a single entity. - * - * The timestamp of the "check" key is treated as being HOLDOFF_TTL seconds in the - * future by get*() methods in order to avoid race conditions where keys are updated - * with stale values (e.g. from a lagged replica DB). A high TTL is set on the "check" - * key, making it possible to know the timestamp of the last change to the corresponding - * entities in most cases. This might use more cache space than resetCheckKey(). - * - * When a few important keys get a large number of hits, a high cache time is usually - * desired as well as "lockTSE" logic. The resetCheckKey() method is less appropriate - * in such cases since the "time since expiry" cannot be inferred, causing any get() - * after the reset to treat the key as being "hot", resulting in more stale value usage. - * - * Note that "check" keys won't collide with other regular keys. - * - * @see WANObjectCache::get() - * @see WANObjectCache::getWithSetCallback() - * @see WANObjectCache::resetCheckKey() - * - * @param string $key Cache key - * @param int $holdoff HOLDOFF_TTL or HOLDOFF_TTL_NONE constant - * @return bool True if the item was purged or not found, false on failure - */ - final public function touchCheckKey( $key, $holdoff = self::HOLDOFF_TTL ) { - // Publish the purge to all datacenters - $ok = $this->relayPurge( self::$TIME_KEY_PREFIX . $key, self::$CHECK_KEY_TTL, $holdoff ); - - $kClass = $this->determineKeyClassForStats( $key ); - $this->stats->increment( "wanobjectcache.$kClass.ck_touch." . ( $ok ? 'ok' : 'error' ) ); - - return $ok; - } - - /** - * Delete a "check" key from all datacenters, invalidating keys that use it - * - * This is similar to touchCheckKey() in that keys using it via get(), getMulti(), - * or getWithSetCallback() will be invalidated. The differences are: - * - a) The "check" key will be deleted from all caches and lazily - * re-initialized when accessed (rather than set everywhere) - * - b) Thus, dependent keys will be known to be stale, but not - * for how long (they are treated as "just" purged), which - * effects any lockTSE logic in getWithSetCallback() - * - c) Since "check" keys are initialized only on the server the key hashes - * to, any temporary ejection of that server will cause the value to be - * seen as purged as a new server will initialize the "check" key. - * - * The advantage here is that the "check" keys, which have high TTLs, will only - * be created when a get*() method actually uses that key. This is better when - * a large number of "check" keys are invalided in a short period of time. - * - * Note that "check" keys won't collide with other regular keys. - * - * @see WANObjectCache::get() - * @see WANObjectCache::getWithSetCallback() - * @see WANObjectCache::touchCheckKey() - * - * @param string $key Cache key - * @return bool True if the item was purged or not found, false on failure - */ - final public function resetCheckKey( $key ) { - // Publish the purge to all datacenters - $ok = $this->relayDelete( self::$TIME_KEY_PREFIX . $key ); - - $kClass = $this->determineKeyClassForStats( $key ); - $this->stats->increment( "wanobjectcache.$kClass.ck_reset." . ( $ok ? 'ok' : 'error' ) ); - - return $ok; - } - - /** - * Method to fetch/regenerate cache keys - * - * On cache miss, the key will be set to the callback result via set() - * (unless the callback returns false) and that result will be returned. - * The arguments supplied to the callback are: - * - $oldValue : current cache value or false if not present - * - &$ttl : a reference to the TTL which can be altered - * - &$setOpts : a reference to options for set() which can be altered - * - $oldAsOf : generation UNIX timestamp of $oldValue or null if not present (since 1.28) - * - * It is strongly recommended to set the 'lag' and 'since' fields to avoid race conditions - * that can cause stale values to get stuck at keys. Usually, callbacks ignore the current - * value, but it can be used to maintain "most recent X" values that come from time or - * sequence based source data, provided that the "as of" id/time is tracked. Note that - * preemptive regeneration and $checkKeys can result in a non-false current value. - * - * Usage of $checkKeys is similar to get() and getMulti(). However, rather than the caller - * having to inspect a "current time left" variable (e.g. $curTTL, $curTTLs), a cache - * regeneration will automatically be triggered using the callback. - * - * The $ttl argument and "hotTTR" option (in $opts) use time-dependant randomization - * to avoid stampedes. Keys that are slow to regenerate and either heavily used - * or subject to explicit (unpredictable) purges, may need additional mechanisms. - * The simplest way to avoid stampedes for such keys is to use 'lockTSE' (in $opts). - * If explicit purges are needed, also: - * - a) Pass $key into $checkKeys - * - b) Use touchCheckKey( $key ) instead of delete( $key ) - * - * Example usage (typical key): - * @code - * $catInfo = $cache->getWithSetCallback( - * // Key to store the cached value under - * $cache->makeKey( 'cat-attributes', $catId ), - * // Time-to-live (in seconds) - * $cache::TTL_MINUTE, - * // Function that derives the new key value - * function ( $oldValue, &$ttl, array &$setOpts ) { - * $dbr = wfGetDB( DB_REPLICA ); - * // Account for any snapshot/replica DB lag - * $setOpts += Database::getCacheSetOptions( $dbr ); - * - * return $dbr->selectRow( ... ); - * } - * ); - * @endcode - * - * Example usage (key that is expensive and hot): - * @code - * $catConfig = $cache->getWithSetCallback( - * // Key to store the cached value under - * $cache->makeKey( 'site-cat-config' ), - * // Time-to-live (in seconds) - * $cache::TTL_DAY, - * // Function that derives the new key value - * function ( $oldValue, &$ttl, array &$setOpts ) { - * $dbr = wfGetDB( DB_REPLICA ); - * // Account for any snapshot/replica DB lag - * $setOpts += Database::getCacheSetOptions( $dbr ); - * - * return CatConfig::newFromRow( $dbr->selectRow( ... ) ); - * }, - * [ - * // Calling touchCheckKey() on this key invalidates the cache - * 'checkKeys' => [ $cache->makeKey( 'site-cat-config' ) ], - * // Try to only let one datacenter thread manage cache updates at a time - * 'lockTSE' => 30, - * // Avoid querying cache servers multiple times in a web request - * 'pcTTL' => $cache::TTL_PROC_LONG - * ] - * ); - * @endcode - * - * Example usage (key with dynamic dependencies): - * @code - * $catState = $cache->getWithSetCallback( - * // Key to store the cached value under - * $cache->makeKey( 'cat-state', $cat->getId() ), - * // Time-to-live (seconds) - * $cache::TTL_HOUR, - * // Function that derives the new key value - * function ( $oldValue, &$ttl, array &$setOpts ) { - * // Determine new value from the DB - * $dbr = wfGetDB( DB_REPLICA ); - * // Account for any snapshot/replica DB lag - * $setOpts += Database::getCacheSetOptions( $dbr ); - * - * return CatState::newFromResults( $dbr->select( ... ) ); - * }, - * [ - * // The "check" keys that represent things the value depends on; - * // Calling touchCheckKey() on any of them invalidates the cache - * 'checkKeys' => [ - * $cache->makeKey( 'sustenance-bowls', $cat->getRoomId() ), - * $cache->makeKey( 'people-present', $cat->getHouseId() ), - * $cache->makeKey( 'cat-laws', $cat->getCityId() ), - * ] - * ] - * ); - * @endcode - * - * Example usage (key that is expensive with too many DB dependencies for "check keys"): - * @code - * $catToys = $cache->getWithSetCallback( - * // Key to store the cached value under - * $cache->makeKey( 'cat-toys', $catId ), - * // Time-to-live (seconds) - * $cache::TTL_HOUR, - * // Function that derives the new key value - * function ( $oldValue, &$ttl, array &$setOpts ) { - * // Determine new value from the DB - * $dbr = wfGetDB( DB_REPLICA ); - * // Account for any snapshot/replica DB lag - * $setOpts += Database::getCacheSetOptions( $dbr ); - * - * return CatToys::newFromResults( $dbr->select( ... ) ); - * }, - * [ - * // Get the highest timestamp of any of the cat's toys - * 'touchedCallback' => function ( $value ) use ( $catId ) { - * $dbr = wfGetDB( DB_REPLICA ); - * $ts = $dbr->selectField( 'cat_toys', 'MAX(ct_touched)', ... ); - * - * return wfTimestampOrNull( TS_UNIX, $ts ); - * }, - * // Avoid DB queries for repeated access - * 'pcTTL' => $cache::TTL_PROC_SHORT - * ] - * ); - * @endcode - * - * Example usage (hot key holding most recent 100 events): - * @code - * $lastCatActions = $cache->getWithSetCallback( - * // Key to store the cached value under - * $cache->makeKey( 'cat-last-actions', 100 ), - * // Time-to-live (in seconds) - * 10, - * // Function that derives the new key value - * function ( $oldValue, &$ttl, array &$setOpts ) { - * $dbr = wfGetDB( DB_REPLICA ); - * // Account for any snapshot/replica DB lag - * $setOpts += Database::getCacheSetOptions( $dbr ); - * - * // Start off with the last cached list - * $list = $oldValue ?: []; - * // Fetch the last 100 relevant rows in descending order; - * // only fetch rows newer than $list[0] to reduce scanning - * $rows = iterator_to_array( $dbr->select( ... ) ); - * // Merge them and get the new "last 100" rows - * return array_slice( array_merge( $new, $list ), 0, 100 ); - * }, - * [ - * // Try to only let one datacenter thread manage cache updates at a time - * 'lockTSE' => 30, - * // Use a magic value when no cache value is ready rather than stampeding - * 'busyValue' => 'computing' - * ] - * ); - * @endcode - * - * Example usage (key holding an LRU subkey:value map; this can avoid flooding cache with - * keys for an unlimited set of (constraint,situation) pairs, thereby avoiding elevated - * cache evictions and wasted memory): - * @code - * $catSituationTolerabilityCache = $this->cache->getWithSetCallback( - * // Group by constraint ID/hash, cat family ID/hash, or something else useful - * $this->cache->makeKey( 'cat-situation-tolerability-checks', $groupKey ), - * WANObjectCache::TTL_DAY, // rarely used groups should fade away - * // The $scenarioKey format is $constraintId: - * function ( $cacheMap ) use ( $scenarioKey, $constraintId, $situation ) { - * $lruCache = MapCacheLRU::newFromArray( $cacheMap ?: [], self::CACHE_SIZE ); - * $result = $lruCache->get( $scenarioKey ); // triggers LRU bump if present - * if ( $result === null || $this->isScenarioResultExpired( $result ) ) { - * $result = $this->checkScenarioTolerability( $constraintId, $situation ); - * $lruCache->set( $scenarioKey, $result, 3 / 8 ); - * } - * // Save the new LRU cache map and reset the map's TTL - * return $lruCache->toArray(); - * }, - * [ - * // Once map is > 1 sec old, consider refreshing - * 'ageNew' => 1, - * // Update within 5 seconds after "ageNew" given a 1hz cache check rate - * 'hotTTR' => 5, - * // Avoid querying cache servers multiple times in a request; this also means - * // that a request can only alter the value of any given constraint key once - * 'pcTTL' => WANObjectCache::TTL_PROC_LONG - * ] - * ); - * $tolerability = isset( $catSituationTolerabilityCache[$scenarioKey] ) - * ? $catSituationTolerabilityCache[$scenarioKey] - * : $this->checkScenarioTolerability( $constraintId, $situation ); - * @endcode - * - * @see WANObjectCache::get() - * @see WANObjectCache::set() - * - * @param string $key Cache key made from makeKey() or makeGlobalKey() - * @param int $ttl Seconds to live for key updates. Special values are: - * - WANObjectCache::TTL_INDEFINITE: Cache forever (subject to LRU-style evictions) - * - WANObjectCache::TTL_UNCACHEABLE: Do not cache (if the key exists, it is not deleted) - * @param callable $callback Value generation function - * @param array $opts Options map: - * - checkKeys: List of "check" keys. The key at $key will be seen as stale when either - * touchCheckKey() or resetCheckKey() is called on any of the keys in this list. This - * is useful if thousands or millions of keys depend on the same entity. The entity can - * simply have its "check" key updated whenever the entity is modified. - * Default: []. - * - graceTTL: If the key is invalidated (by "checkKeys"/"touchedCallback") less than this - * many seconds ago, consider reusing the stale value. The odds of a refresh becomes - * more likely over time, becoming certain once the grace period is reached. This can - * reduce traffic spikes when millions of keys are compared to the same "check" key and - * touchCheckKey() or resetCheckKey() is called on that "check" key. This option is not - * useful for avoiding traffic spikes in the case of the key simply expiring on account - * of its TTL (use "lowTTL" instead). - * Default: WANObjectCache::GRACE_TTL_NONE. - * - lockTSE: If the key is tombstoned or invalidated (by "checkKeys"/"touchedCallback") - * less than this many seconds ago, try to have a single thread handle cache regeneration - * at any given time. Other threads will use stale values if possible. If, on miss, - * the time since expiration is low, the assumption is that the key is hot and that a - * stampede is worth avoiding. Note that if the key falls out of cache then concurrent - * threads will all run the callback on cache miss until the value is saved in cache. - * The only stampede protection in that case is from duplicate cache sets when the - * callback takes longer than WANObjectCache::SET_DELAY_HIGH_MS milliseconds; consider - * using "busyValue" if such stampedes are a problem. Note that the higher "lockTSE" is - * set, the higher the worst-case staleness of returned values can be. Also note that - * this option does not by itself handle the case of the key simply expiring on account - * of its TTL, so make sure that "lowTTL" is not disabled when using this option. Avoid - * combining this option with delete() as it can always cause a stampede due to their - * being no stale value available until after a thread completes the callback. - * Use WANObjectCache::TSE_NONE to disable this logic. - * Default: WANObjectCache::TSE_NONE. - * - busyValue: Specify a placeholder value to use when no value exists and another thread - * is currently regenerating it. This assures that cache stampedes cannot happen if the - * value falls out of cache. This also mitigates stampedes when value regeneration - * becomes very slow (greater than $ttl/"lowTTL"). If this is a closure, then it will - * be invoked to get the placeholder when needed. - * Default: null. - * - pcTTL: Process cache the value in this PHP instance for this many seconds. This avoids - * network I/O when a key is read several times. This will not cache when the callback - * returns false, however. Note that any purges will not be seen while process cached; - * since the callback should use replica DBs and they may be lagged or have snapshot - * isolation anyway, this should not typically matter. - * Default: WANObjectCache::TTL_UNCACHEABLE. - * - pcGroup: Process cache group to use instead of the primary one. If set, this must be - * of the format ALPHANUMERIC_NAME:MAX_KEY_SIZE, e.g. "mydata:10". Use this for storing - * large values, small yet numerous values, or some values with a high cost of eviction. - * It is generally preferable to use a class constant when setting this value. - * This has no effect unless pcTTL is used. - * Default: WANObjectCache::PC_PRIMARY. - * - version: Integer version number. This lets callers make breaking changes to the format - * of cached values without causing problems for sites that use non-instantaneous code - * deployments. Old and new code will recognize incompatible versions and purges from - * both old and new code will been seen by each other. When this method encounters an - * incompatibly versioned value at the provided key, a "variant key" will be used for - * reading from and saving to cache. The variant key is specific to the key and version - * number provided to this method. If the variant key value is older than that of the - * provided key, or the provided key is non-existant, then the variant key will be seen - * as non-existant. Therefore, delete() calls invalidate the provided key's variant keys. - * The "checkKeys" and "touchedCallback" options still apply to variant keys as usual. - * Avoid storing class objects, as this reduces compatibility (due to serialization). - * Default: null. - * - minAsOf: Reject values if they were generated before this UNIX timestamp. - * This is useful if the source of a key is suspected of having possibly changed - * recently, and the caller wants any such changes to be reflected. - * Default: WANObjectCache::MIN_TIMESTAMP_NONE. - * - hotTTR: Expected time-till-refresh (TTR) in seconds for keys that average ~1 hit per - * second (e.g. 1Hz). Keys with a hit rate higher than 1Hz will refresh sooner than this - * TTR and vise versa. Such refreshes won't happen until keys are "ageNew" seconds old. - * This uses randomization to avoid triggering cache stampedes. The TTR is useful at - * reducing the impact of missed cache purges, since the effect of a heavily referenced - * key being stale is worse than that of a rarely referenced key. Unlike simply lowering - * $ttl, seldomly used keys are largely unaffected by this option, which makes it - * possible to have a high hit rate for the "long-tail" of less-used keys. - * Default: WANObjectCache::HOT_TTR. - * - lowTTL: Consider pre-emptive updates when the current TTL (seconds) of the key is less - * than this. It becomes more likely over time, becoming certain once the key is expired. - * This helps avoid cache stampedes that might be triggered due to the key expiring. - * Default: WANObjectCache::LOW_TTL. - * - ageNew: Consider popularity refreshes only once a key reaches this age in seconds. - * Default: WANObjectCache::AGE_NEW. - * - staleTTL: Seconds to keep the key around if it is stale. This means that on cache - * miss the callback may get $oldValue/$oldAsOf values for keys that have already been - * expired for this specified time. This is useful if adaptiveTTL() is used on the old - * value's as-of time when it is verified as still being correct. - * Default: WANObjectCache::STALE_TTL_NONE - * - touchedCallback: A callback that takes the current value and returns a UNIX timestamp - * indicating the last time a dynamic dependency changed. Null can be returned if there - * are no relevant dependency changes to check. This can be used to check against things - * like last-modified times of files or DB timestamp fields. This should generally not be - * used for small and easily queried values in a DB if the callback itself ends up doing - * a similarly expensive DB query to check a timestamp. Usages of this option makes the - * most sense for values that are moderately to highly expensive to regenerate and easy - * to query for dependency timestamps. The use of "pcTTL" reduces timestamp queries. - * Default: null. - * @return mixed Value found or written to the key - * @note Options added in 1.28: version, busyValue, hotTTR, ageNew, pcGroup, minAsOf - * @note Options added in 1.31: staleTTL, graceTTL - * @note Options added in 1.33: touchedCallback - * @note Callable type hints are not used to avoid class-autoloading - */ - final public function getWithSetCallback( $key, $ttl, $callback, array $opts = [] ) { - $version = $opts['version'] ?? null; - $pcTTL = $opts['pcTTL'] ?? self::TTL_UNCACHEABLE; - $pCache = ( $pcTTL >= 0 ) - ? $this->getProcessCache( $opts['pcGroup'] ?? self::PC_PRIMARY ) - : null; - - // Use the process cache if requested as long as no outer cache callback is running. - // Nested callback process cache use is not lag-safe with regard to HOLDOFF_TTL since - // process cached values are more lagged than persistent ones as they are not purged. - if ( $pCache && $this->callbackDepth == 0 ) { - $cached = $pCache->get( $this->getProcessCacheKey( $key, $version ), INF, false ); - if ( $cached !== false ) { - return $cached; - } - } - - $res = $this->fetchOrRegenerate( $key, $ttl, $callback, $opts ); - list( $value, $valueVersion, $curAsOf ) = $res; - if ( $valueVersion !== $version ) { - // Current value has a different version; use the variant key for this version. - // Regenerate the variant value if it is not newer than the main value at $key - // so that purges to the main key propagate to the variant value. - list( $value ) = $this->fetchOrRegenerate( - $this->makeGlobalKey( 'WANCache-key-variant', md5( $key ), $version ), - $ttl, - $callback, - [ 'version' => null, 'minAsOf' => $curAsOf ] + $opts - ); - } - - // Update the process cache if enabled - if ( $pCache && $value !== false ) { - $pCache->set( $this->getProcessCacheKey( $key, $version ), $value ); - } - - return $value; - } - - /** - * Do the actual I/O for getWithSetCallback() when needed - * - * @see WANObjectCache::getWithSetCallback() - * - * @param string $key - * @param int $ttl - * @param callable $callback - * @param array $opts Options map for getWithSetCallback() - * @return array Ordered list of the following: - * - Cached or regenerated value - * - Cached or regenerated value version number or null if not versioned - * - Timestamp of the current cached value at the key or null if there is no value - * @note Callable type hints are not used to avoid class-autoloading - */ - private function fetchOrRegenerate( $key, $ttl, $callback, array $opts ) { - $checkKeys = $opts['checkKeys'] ?? []; - $graceTTL = $opts['graceTTL'] ?? self::GRACE_TTL_NONE; - $minAsOf = $opts['minAsOf'] ?? self::MIN_TIMESTAMP_NONE; - $hotTTR = $opts['hotTTR'] ?? self::HOT_TTR; - $lowTTL = $opts['lowTTL'] ?? min( self::LOW_TTL, $ttl ); - $ageNew = $opts['ageNew'] ?? self::AGE_NEW; - $touchedCb = $opts['touchedCallback'] ?? null; - $initialTime = $this->getCurrentTime(); - - $kClass = $this->determineKeyClassForStats( $key ); - - // Get the current key value and its metadata - $curTTL = self::PASS_BY_REF; - $curInfo = self::PASS_BY_REF; /** @var array $curInfo */ - $curValue = $this->get( $key, $curTTL, $checkKeys, $curInfo ); - // Apply any $touchedCb invalidation timestamp to get the "last purge timestamp" - list( $curTTL, $LPT ) = $this->resolveCTL( $curValue, $curTTL, $curInfo, $touchedCb ); - // Use the cached value if it exists and is not due for synchronous regeneration - if ( - $this->isValid( $curValue, $curInfo['asOf'], $minAsOf ) && - $this->isAliveOrInGracePeriod( $curTTL, $graceTTL ) - ) { - $preemptiveRefresh = ( - $this->worthRefreshExpiring( $curTTL, $lowTTL ) || - $this->worthRefreshPopular( $curInfo['asOf'], $ageNew, $hotTTR, $initialTime ) - ); - if ( !$preemptiveRefresh ) { - $this->stats->increment( "wanobjectcache.$kClass.hit.good" ); - - return [ $curValue, $curInfo['version'], $curInfo['asOf'] ]; - } elseif ( $this->scheduleAsyncRefresh( $key, $ttl, $callback, $opts ) ) { - $this->stats->increment( "wanobjectcache.$kClass.hit.refresh" ); - - return [ $curValue, $curInfo['version'], $curInfo['asOf'] ]; - } - } - - // Determine if there is stale or volatile cached value that is still usable - $isKeyTombstoned = ( $curInfo['tombAsOf'] !== null ); - if ( $isKeyTombstoned ) { - // Key is write-holed; use the (volatile) interim key as an alternative - list( $possValue, $possInfo ) = $this->getInterimValue( $key, $minAsOf ); - // Update the "last purge time" since the $touchedCb timestamp depends on $value - $LPT = $this->resolveTouched( $possValue, $LPT, $touchedCb ); - } else { - $possValue = $curValue; - $possInfo = $curInfo; - } - - // Avoid overhead from callback runs, regeneration locks, and cache sets during - // hold-off periods for the key by reusing very recently generated cached values - if ( - $this->isValid( $possValue, $possInfo['asOf'], $minAsOf, $LPT ) && - $this->isVolatileValueAgeNegligible( $initialTime - $possInfo['asOf'] ) - ) { - $this->stats->increment( "wanobjectcache.$kClass.hit.volatile" ); - - return [ $possValue, $possInfo['version'], $curInfo['asOf'] ]; - } - - $lockTSE = $opts['lockTSE'] ?? self::TSE_NONE; - $busyValue = $opts['busyValue'] ?? null; - $staleTTL = $opts['staleTTL'] ?? self::STALE_TTL_NONE; - $version = $opts['version'] ?? null; - - // Determine whether one thread per datacenter should handle regeneration at a time - $useRegenerationLock = - // Note that since tombstones no-op set(), $lockTSE and $curTTL cannot be used to - // deduce the key hotness because |$curTTL| will always keep increasing until the - // tombstone expires or is overwritten by a new tombstone. Also, even if $lockTSE - // is not set, constant regeneration of a key for the tombstone lifetime might be - // very expensive. Assume tombstoned keys are possibly hot in order to reduce - // the risk of high regeneration load after the delete() method is called. - $isKeyTombstoned || - // Assume a key is hot if requested soon ($lockTSE seconds) after invalidation. - // This avoids stampedes when timestamps from $checkKeys/$touchedCb bump. - ( $curTTL !== null && $curTTL <= 0 && abs( $curTTL ) <= $lockTSE ) || - // Assume a key is hot if there is no value and a busy fallback is given. - // This avoids stampedes on eviction or preemptive regeneration taking too long. - ( $busyValue !== null && $possValue === false ); - - // If a regeneration lock is required, threads that do not get the lock will try to use - // the stale value, the interim value, or the $busyValue placeholder, in that order. If - // none of those are set then all threads will bypass the lock and regenerate the value. - $hasLock = $useRegenerationLock && $this->claimStampedeLock( $key ); - if ( $useRegenerationLock && !$hasLock ) { - if ( $this->isValid( $possValue, $possInfo['asOf'], $minAsOf ) ) { - $this->stats->increment( "wanobjectcache.$kClass.hit.stale" ); - - return [ $possValue, $possInfo['version'], $curInfo['asOf'] ]; - } elseif ( $busyValue !== null ) { - $miss = is_infinite( $minAsOf ) ? 'renew' : 'miss'; - $this->stats->increment( "wanobjectcache.$kClass.$miss.busy" ); - - return [ $this->resolveBusyValue( $busyValue ), $version, $curInfo['asOf'] ]; - } - } - - // Generate the new value given any prior value with a matching version - $setOpts = []; - $preCallbackTime = $this->getCurrentTime(); - ++$this->callbackDepth; - try { - $value = $callback( - ( $curInfo['version'] === $version ) ? $curValue : false, - $ttl, - $setOpts, - ( $curInfo['version'] === $version ) ? $curInfo['asOf'] : null - ); - } finally { - --$this->callbackDepth; - } - $postCallbackTime = $this->getCurrentTime(); - - // How long it took to fetch, validate, and generate the value - $elapsed = max( $postCallbackTime - $initialTime, 0.0 ); - - // Attempt to save the newly generated value if applicable - if ( - // Callback yielded a cacheable value - ( $value !== false && $ttl >= 0 ) && - // Current thread was not raced out of a regeneration lock or key is tombstoned - ( !$useRegenerationLock || $hasLock || $isKeyTombstoned ) && - // Key does not appear to be undergoing a set() stampede - $this->checkAndSetCooloff( $key, $kClass, $elapsed, $lockTSE, $hasLock ) - ) { - // How long it took to generate the value - $walltime = max( $postCallbackTime - $preCallbackTime, 0.0 ); - $this->stats->timing( "wanobjectcache.$kClass.regen_walltime", 1e3 * $walltime ); - // If the key is write-holed then use the (volatile) interim key as an alternative - if ( $isKeyTombstoned ) { - $this->setInterimValue( $key, $value, $lockTSE, $version, $walltime ); - } else { - $finalSetOpts = [ - 'since' => $setOpts['since'] ?? $preCallbackTime, - 'version' => $version, - 'staleTTL' => $staleTTL, - 'lockTSE' => $lockTSE, // informs lag vs performance trade-offs - 'creating' => ( $curValue === false ), // optimization - 'walltime' => $walltime - ] + $setOpts; - $this->set( $key, $value, $ttl, $finalSetOpts ); - } - } - - $this->yieldStampedeLock( $key, $hasLock ); - - $miss = is_infinite( $minAsOf ) ? 'renew' : 'miss'; - $this->stats->increment( "wanobjectcache.$kClass.$miss.compute" ); - - return [ $value, $version, $curInfo['asOf'] ]; - } - - /** - * @param string $key - * @return bool Success - */ - private function claimStampedeLock( $key ) { - // Note that locking is not bypassed due to I/O errors; this avoids stampedes - return $this->cache->add( self::$MUTEX_KEY_PREFIX . $key, 1, self::$LOCK_TTL ); - } - - /** - * @param string $key - * @param bool $hasLock - */ - private function yieldStampedeLock( $key, $hasLock ) { - if ( $hasLock ) { - // The backend might be a mcrouter proxy set to broadcast DELETE to *all* the local - // datacenter cache servers via OperationSelectorRoute (for increased consistency). - // Since that would be excessive for these locks, use TOUCH to expire the key. - $this->cache->changeTTL( self::$MUTEX_KEY_PREFIX . $key, $this->getCurrentTime() - 60 ); - } - } - - /** - * @param float $age Age of volatile/interim key in seconds - * @return bool Whether the age of a volatile value is negligible - */ - private function isVolatileValueAgeNegligible( $age ) { - return ( $age < mt_rand( self::$RECENT_SET_LOW_MS, self::$RECENT_SET_HIGH_MS ) / 1e3 ); - } - - /** - * @param string $key - * @param string $kClass - * @param float $elapsed Seconds spent regenerating the value - * @param float $lockTSE - * @param bool $hasLock - * @return bool Whether it is OK to proceed with a key set operation - */ - private function checkAndSetCooloff( $key, $kClass, $elapsed, $lockTSE, $hasLock ) { - $this->stats->timing( "wanobjectcache.$kClass.regen_set_delay", 1e3 * $elapsed ); - - // If $lockTSE is set, the lock was bypassed because there was no stale/interim value, - // and $elapsed indicates that regeration is slow, then there is a risk of set() - // stampedes with large blobs. With a typical scale-out infrastructure, CPU and query - // load from $callback invocations is distributed among appservers and replica DBs, - // but cache operations for a given key route to a single cache server (e.g. striped - // consistent hashing). - if ( $lockTSE < 0 || $hasLock ) { - return true; // either not a priori hot or thread has the lock - } elseif ( $elapsed <= self::$SET_DELAY_HIGH_MS * 1e3 ) { - return true; // not enough time for threads to pile up - } - - $this->cache->clearLastError(); - if ( - !$this->cache->add( self::$COOLOFF_KEY_PREFIX . $key, 1, self::$COOLOFF_TTL ) && - // Don't treat failures due to I/O errors as the key being in cooloff - $this->cache->getLastError() === BagOStuff::ERR_NONE - ) { - $this->stats->increment( "wanobjectcache.$kClass.cooloff_bounce" ); - - return false; - } - - return true; - } - - /** - * @param mixed $value - * @param float|null $curTTL - * @param array $curInfo - * @param callable|null $touchedCallback - * @return array (current time left or null, UNIX timestamp of last purge or null) - * @note Callable type hints are not used to avoid class-autoloading - */ - private function resolveCTL( $value, $curTTL, $curInfo, $touchedCallback ) { - if ( $touchedCallback === null || $value === false ) { - return [ $curTTL, max( $curInfo['tombAsOf'], $curInfo['lastCKPurge'] ) ]; - } - - $touched = $touchedCallback( $value ); - if ( $touched !== null && $touched >= $curInfo['asOf'] ) { - $curTTL = min( $curTTL, self::$TINY_NEGATIVE, $curInfo['asOf'] - $touched ); - } - - return [ $curTTL, max( $curInfo['tombAsOf'], $curInfo['lastCKPurge'], $touched ) ]; - } - - /** - * @param mixed $value - * @param float|null $lastPurge - * @param callable|null $touchedCallback - * @return float|null UNIX timestamp of last purge or null - * @note Callable type hints are not used to avoid class-autoloading - */ - private function resolveTouched( $value, $lastPurge, $touchedCallback ) { - return ( $touchedCallback === null || $value === false ) - ? $lastPurge // nothing to derive the "touched timestamp" from - : max( $touchedCallback( $value ), $lastPurge ); - } - - /** - * @param string $key - * @param float $minAsOf Minimum acceptable "as of" timestamp - * @return array (cached value or false, cache key metadata map) - */ - private function getInterimValue( $key, $minAsOf ) { - $now = $this->getCurrentTime(); - - if ( $this->useInterimHoldOffCaching ) { - $wrapped = $this->cache->get( self::$INTERIM_KEY_PREFIX . $key ); - - list( $value, $keyInfo ) = $this->unwrap( $wrapped, $now ); - if ( $this->isValid( $value, $keyInfo['asOf'], $minAsOf ) ) { - return [ $value, $keyInfo ]; - } - } - - return $this->unwrap( false, $now ); - } - - /** - * @param string $key - * @param mixed $value - * @param int $ttl - * @param int|null $version Value version number - * @param float $walltime How long it took to generate the value in seconds - */ - private function setInterimValue( $key, $value, $ttl, $version, $walltime ) { - $ttl = max( self::$INTERIM_KEY_TTL, (int)$ttl ); - - $wrapped = $this->wrap( $value, $ttl, $version, $this->getCurrentTime(), $walltime ); - $this->cache->merge( - self::$INTERIM_KEY_PREFIX . $key, - function () use ( $wrapped ) { - return $wrapped; - }, - $ttl, - 1 - ); - } - - /** - * @param mixed $busyValue - * @return mixed - */ - private function resolveBusyValue( $busyValue ) { - return ( $busyValue instanceof Closure ) ? $busyValue() : $busyValue; - } - - /** - * Method to fetch multiple cache keys at once with regeneration - * - * This works the same as getWithSetCallback() except: - * - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys() - * - b) The $callback argument expects a callback taking the following arguments: - * - $id: ID of an entity to query - * - $oldValue : the prior cache value or false if none was present - * - &$ttl : a reference to the new value TTL in seconds - * - &$setOpts : a reference to options for set() which can be altered - * - $oldAsOf : generation UNIX timestamp of $oldValue or null if not present - * Aside from the additional $id argument, the other arguments function the same - * way they do in getWithSetCallback(). - * - c) The return value is a map of (cache key => value) in the order of $keyedIds - * - * @see WANObjectCache::getWithSetCallback() - * @see WANObjectCache::getMultiWithUnionSetCallback() - * - * Example usage: - * @code - * $rows = $cache->getMultiWithSetCallback( - * // Map of cache keys to entity IDs - * $cache->makeMultiKeys( - * $this->fileVersionIds(), - * function ( $id ) use ( $cache ) { - * return $cache->makeKey( 'file-version', $id ); - * } - * ), - * // Time-to-live (in seconds) - * $cache::TTL_DAY, - * // Function that derives the new key value - * function ( $id, $oldValue, &$ttl, array &$setOpts ) { - * $dbr = wfGetDB( DB_REPLICA ); - * // Account for any snapshot/replica DB lag - * $setOpts += Database::getCacheSetOptions( $dbr ); - * - * // Load the row for this file - * $queryInfo = File::getQueryInfo(); - * $row = $dbr->selectRow( - * $queryInfo['tables'], - * $queryInfo['fields'], - * [ 'id' => $id ], - * __METHOD__, - * [], - * $queryInfo['joins'] - * ); - * - * return $row ? (array)$row : false; - * }, - * [ - * // Process cache for 30 seconds - * 'pcTTL' => 30, - * // Use a dedicated 500 item cache (initialized on-the-fly) - * 'pcGroup' => 'file-versions:500' - * ] - * ); - * $files = array_map( [ __CLASS__, 'newFromRow' ], $rows ); - * @endcode - * - * @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys() - * @param int $ttl Seconds to live for key updates - * @param callable $callback Callback the yields entity regeneration callbacks - * @param array $opts Options map - * @return mixed[] Map of (cache key => value) in the same order as $keyedIds - * @since 1.28 - */ - final public function getMultiWithSetCallback( - ArrayIterator $keyedIds, $ttl, callable $callback, array $opts = [] - ) { - // Load required keys into process cache in one go - $this->warmupCache = $this->getRawKeysForWarmup( - $this->getNonProcessCachedMultiKeys( $keyedIds, $opts ), - $opts['checkKeys'] ?? [] - ); - $this->warmupKeyMisses = 0; - - // Wrap $callback to match the getWithSetCallback() format while passing $id to $callback - $id = null; // current entity ID - $func = function ( $oldValue, &$ttl, &$setOpts, $oldAsOf ) use ( $callback, &$id ) { - return $callback( $id, $oldValue, $ttl, $setOpts, $oldAsOf ); - }; - - $values = []; - foreach ( $keyedIds as $key => $id ) { // preserve order - $values[$key] = $this->getWithSetCallback( $key, $ttl, $func, $opts ); - } - - $this->warmupCache = []; - - return $values; - } - - /** - * Method to fetch/regenerate multiple cache keys at once - * - * This works the same as getWithSetCallback() except: - * - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys() - * - b) The $callback argument expects a callback returning a map of (ID => new value) - * for all entity IDs in $ids and it takes the following arguments: - * - $ids: a list of entity IDs that require cache regeneration - * - &$ttls: a reference to the (entity ID => new TTL) map - * - &$setOpts: a reference to options for set() which can be altered - * - c) The return value is a map of (cache key => value) in the order of $keyedIds - * - d) The "lockTSE" and "busyValue" options are ignored - * - * @see WANObjectCache::getWithSetCallback() - * @see WANObjectCache::getMultiWithSetCallback() - * - * Example usage: - * @code - * $rows = $cache->getMultiWithUnionSetCallback( - * // Map of cache keys to entity IDs - * $cache->makeMultiKeys( - * $this->fileVersionIds(), - * function ( $id ) use ( $cache ) { - * return $cache->makeKey( 'file-version', $id ); - * } - * ), - * // Time-to-live (in seconds) - * $cache::TTL_DAY, - * // Function that derives the new key value - * function ( array $ids, array &$ttls, array &$setOpts ) { - * $dbr = wfGetDB( DB_REPLICA ); - * // Account for any snapshot/replica DB lag - * $setOpts += Database::getCacheSetOptions( $dbr ); - * - * // Load the rows for these files - * $rows = []; - * $queryInfo = File::getQueryInfo(); - * $res = $dbr->select( - * $queryInfo['tables'], - * $queryInfo['fields'], - * [ 'id' => $ids ], - * __METHOD__, - * [], - * $queryInfo['joins'] - * ); - * foreach ( $res as $row ) { - * $rows[$row->id] = $row; - * $mtime = wfTimestamp( TS_UNIX, $row->timestamp ); - * $ttls[$row->id] = $this->adaptiveTTL( $mtime, $ttls[$row->id] ); - * } - * - * return $rows; - * }, - * ] - * ); - * $files = array_map( [ __CLASS__, 'newFromRow' ], $rows ); - * @endcode - * - * @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys() - * @param int $ttl Seconds to live for key updates - * @param callable $callback Callback the yields entity regeneration callbacks - * @param array $opts Options map - * @return mixed[] Map of (cache key => value) in the same order as $keyedIds - * @since 1.30 - */ - final public function getMultiWithUnionSetCallback( - ArrayIterator $keyedIds, $ttl, callable $callback, array $opts = [] - ) { - $checkKeys = $opts['checkKeys'] ?? []; - unset( $opts['lockTSE'] ); // incompatible - unset( $opts['busyValue'] ); // incompatible - - // Load required keys into process cache in one go - $keysByIdGet = $this->getNonProcessCachedMultiKeys( $keyedIds, $opts ); - $this->warmupCache = $this->getRawKeysForWarmup( $keysByIdGet, $checkKeys ); - $this->warmupKeyMisses = 0; - - // IDs of entities known to be in need of regeneration - $idsRegen = []; - - // Find out which keys are missing/deleted/stale - $curTTLs = []; - $asOfs = []; - $curByKey = $this->getMulti( $keysByIdGet, $curTTLs, $checkKeys, $asOfs ); - foreach ( $keysByIdGet as $id => $key ) { - if ( !array_key_exists( $key, $curByKey ) || $curTTLs[$key] < 0 ) { - $idsRegen[] = $id; - } - } - - // Run the callback to populate the regeneration value map for all required IDs - $newSetOpts = []; - $newTTLsById = array_fill_keys( $idsRegen, $ttl ); - $newValsById = $idsRegen ? $callback( $idsRegen, $newTTLsById, $newSetOpts ) : []; - - // Wrap $callback to match the getWithSetCallback() format while passing $id to $callback - $id = null; // current entity ID - $func = function ( $oldValue, &$ttl, &$setOpts, $oldAsOf ) - use ( $callback, &$id, $newValsById, $newTTLsById, $newSetOpts ) - { - if ( array_key_exists( $id, $newValsById ) ) { - // Value was already regerated as expected, so use the value in $newValsById - $newValue = $newValsById[$id]; - $ttl = $newTTLsById[$id]; - $setOpts = $newSetOpts; - } else { - // Pre-emptive/popularity refresh and version mismatch cases are not detected - // above and thus $newValsById has no entry. Run $callback on this single entity. - $ttls = [ $id => $ttl ]; - $newValue = $callback( [ $id ], $ttls, $setOpts )[$id]; - $ttl = $ttls[$id]; - } - - return $newValue; - }; - - // Run the cache-aside logic using warmupCache instead of persistent cache queries - $values = []; - foreach ( $keyedIds as $key => $id ) { // preserve order - $values[$key] = $this->getWithSetCallback( $key, $ttl, $func, $opts ); - } - - $this->warmupCache = []; - - return $values; - } - - /** - * Set a key to soon expire in the local cluster if it pre-dates $purgeTimestamp - * - * This sets stale keys' time-to-live at HOLDOFF_TTL seconds, which both avoids - * broadcasting in mcrouter setups and also avoids races with new tombstones. - * - * @param string $key Cache key - * @param int $purgeTimestamp UNIX timestamp of purge - * @param bool &$isStale Whether the key is stale - * @return bool Success - * @since 1.28 - */ - final public function reap( $key, $purgeTimestamp, &$isStale = false ) { - $minAsOf = $purgeTimestamp + self::HOLDOFF_TTL; - $wrapped = $this->cache->get( self::$VALUE_KEY_PREFIX . $key ); - if ( is_array( $wrapped ) && $wrapped[self::$FLD_TIME] < $minAsOf ) { - $isStale = true; - $this->logger->warning( "Reaping stale value key '$key'." ); - $ttlReap = self::HOLDOFF_TTL; // avoids races with tombstone creation - $ok = $this->cache->changeTTL( self::$VALUE_KEY_PREFIX . $key, $ttlReap ); - if ( !$ok ) { - $this->logger->error( "Could not complete reap of key '$key'." ); - } - - return $ok; - } - - $isStale = false; - - return true; - } - - /** - * Set a "check" key to soon expire in the local cluster if it pre-dates $purgeTimestamp - * - * @param string $key Cache key - * @param int $purgeTimestamp UNIX timestamp of purge - * @param bool &$isStale Whether the key is stale - * @return bool Success - * @since 1.28 - */ - final public function reapCheckKey( $key, $purgeTimestamp, &$isStale = false ) { - $purge = $this->parsePurgeValue( $this->cache->get( self::$TIME_KEY_PREFIX . $key ) ); - if ( $purge && $purge[self::$PURGE_TIME] < $purgeTimestamp ) { - $isStale = true; - $this->logger->warning( "Reaping stale check key '$key'." ); - $ok = $this->cache->changeTTL( self::$TIME_KEY_PREFIX . $key, self::TTL_SECOND ); - if ( !$ok ) { - $this->logger->error( "Could not complete reap of check key '$key'." ); - } - - return $ok; - } - - $isStale = false; - - return false; - } - - /** - * @see BagOStuff::makeKey() - * @param string $class Key class - * @param string ...$components Key components (starting with a key collection name) - * @return string Colon-delimited list of $keyspace followed by escaped components - * @since 1.27 - */ - public function makeKey( $class, ...$components ) { - return $this->cache->makeKey( ...func_get_args() ); - } - - /** - * @see BagOStuff::makeGlobalKey() - * @param string $class Key class - * @param string ...$components Key components (starting with a key collection name) - * @return string Colon-delimited list of $keyspace followed by escaped components - * @since 1.27 - */ - public function makeGlobalKey( $class, ...$components ) { - return $this->cache->makeGlobalKey( ...func_get_args() ); - } - - /** - * Hash a possibly long string into a suitable component for makeKey()/makeGlobalKey() - * - * @param string $component A raw component used in building a cache key - * @return string 64 character HMAC using a stable secret for public collision resistance - * @since 1.34 - */ - public function hash256( $component ) { - return hash_hmac( 'sha256', $component, $this->secret ); - } - - /** - * Get an iterator of (cache key => entity ID) for a list of entity IDs - * - * The callback takes an ID string and returns a key via makeKey()/makeGlobalKey(). - * There should be no network nor filesystem I/O used in the callback. The entity - * ID/key mapping must be 1:1 or an exception will be thrown. If hashing is needed, - * then use the hash256() method. - * - * Example usage for the default keyspace: - * @code - * $keyedIds = $cache->makeMultiKeys( - * $modules, - * function ( $module ) use ( $cache ) { - * return $cache->makeKey( 'module-info', $module ); - * } - * ); - * @endcode - * - * Example usage for mixed default and global keyspace: - * @code - * $keyedIds = $cache->makeMultiKeys( - * $filters, - * function ( $filter ) use ( $cache ) { - * return ( strpos( $filter, 'central:' ) === 0 ) - * ? $cache->makeGlobalKey( 'regex-filter', $filter ) - * : $cache->makeKey( 'regex-filter', $filter ) - * } - * ); - * @endcode - * - * Example usage with hashing: - * @code - * $keyedIds = $cache->makeMultiKeys( - * $urls, - * function ( $url ) use ( $cache ) { - * return $cache->makeKey( 'url-info', $cache->hash256( $url ) ); - * } - * ); - * @endcode - * - * @see WANObjectCache::makeKey() - * @see WANObjectCache::makeGlobalKey() - * @see WANObjectCache::hash256() - * - * @param string[]|int[] $ids List of entity IDs - * @param callable $keyCallback Function returning makeKey()/makeGlobalKey() on the input ID - * @return ArrayIterator Iterator of (cache key => ID); order of $ids is preserved - * @throws UnexpectedValueException - * @since 1.28 - */ - final public function makeMultiKeys( array $ids, $keyCallback ) { - $idByKey = []; - foreach ( $ids as $id ) { - // Discourage triggering of automatic makeKey() hashing in some backends - if ( strlen( $id ) > 64 ) { - $this->logger->warning( __METHOD__ . ": long ID '$id'; use hash256()" ); - } - $key = $keyCallback( $id, $this ); - // Edge case: ignore key collisions due to duplicate $ids like "42" and 42 - if ( !isset( $idByKey[$key] ) ) { - $idByKey[$key] = $id; - } elseif ( (string)$id !== (string)$idByKey[$key] ) { - throw new UnexpectedValueException( - "Cache key collision; IDs ('$id','{$idByKey[$key]}') map to '$key'" - ); - } - } - - return new ArrayIterator( $idByKey ); - } - - /** - * Get an (ID => value) map from (i) a non-unique list of entity IDs, and (ii) the list - * of corresponding entity values by first appearance of each ID in the entity ID list - * - * For use with getMultiWithSetCallback() and getMultiWithUnionSetCallback(). - * - * *Only* use this method if the entity ID/key mapping is trivially 1:1 without exception. - * Key generation method must utitilize the *full* entity ID in the key (not a hash of it). - * - * Example usage: - * @code - * $poems = $cache->getMultiWithSetCallback( - * $cache->makeMultiKeys( - * $uuids, - * function ( $uuid ) use ( $cache ) { - * return $cache->makeKey( 'poem', $uuid ); - * } - * ), - * $cache::TTL_DAY, - * function ( $uuid ) use ( $url ) { - * return $this->http->run( [ 'method' => 'GET', 'url' => "$url/$uuid" ] ); - * } - * ); - * $poemsByUUID = $cache->multiRemap( $uuids, $poems ); - * @endcode - * - * @see WANObjectCache::makeMultiKeys() - * @see WANObjectCache::getMultiWithSetCallback() - * @see WANObjectCache::getMultiWithUnionSetCallback() - * - * @param string[]|int[] $ids Entity ID list makeMultiKeys() - * @param mixed[] $res Result of getMultiWithSetCallback()/getMultiWithUnionSetCallback() - * @return mixed[] Map of (ID => value); order of $ids is preserved - * @since 1.34 - */ - final public function multiRemap( array $ids, array $res ) { - if ( count( $ids ) !== count( $res ) ) { - // If makeMultiKeys() is called on a list of non-unique IDs, then the resulting - // ArrayIterator will have less entries due to "first appearance" de-duplication - $ids = array_keys( array_flip( $ids ) ); - if ( count( $ids ) !== count( $res ) ) { - throw new UnexpectedValueException( "Multi-key result does not match ID list" ); - } - } - - return array_combine( $ids, $res ); - } - - /** - * Get the "last error" registered; clearLastError() should be called manually - * @return int ERR_* class constant for the "last error" registry - */ - final public function getLastError() { - $code = $this->cache->getLastError(); - switch ( $code ) { - case BagOStuff::ERR_NONE: - return self::ERR_NONE; - case BagOStuff::ERR_NO_RESPONSE: - return self::ERR_NO_RESPONSE; - case BagOStuff::ERR_UNREACHABLE: - return self::ERR_UNREACHABLE; - default: - return self::ERR_UNEXPECTED; - } - } - - /** - * Clear the "last error" registry - */ - final public function clearLastError() { - $this->cache->clearLastError(); - } - - /** - * Clear the in-process caches; useful for testing - * - * @since 1.27 - */ - public function clearProcessCache() { - $this->processCaches = []; - } - - /** - * Enable or disable the use of brief caching for tombstoned keys - * - * When a key is purged via delete(), there normally is a period where caching - * is hold-off limited to an extremely short time. This method will disable that - * caching, forcing the callback to run for any of: - * - WANObjectCache::getWithSetCallback() - * - WANObjectCache::getMultiWithSetCallback() - * - WANObjectCache::getMultiWithUnionSetCallback() - * - * This is useful when both: - * - a) the database used by the callback is known to be up-to-date enough - * for some particular purpose (e.g. replica DB has applied transaction X) - * - b) the caller needs to exploit that fact, and therefore needs to avoid the - * use of inherently volatile and possibly stale interim keys - * - * @see WANObjectCache::delete() - * @param bool $enabled Whether to enable interim caching - * @since 1.31 - */ - final public function useInterimHoldOffCaching( $enabled ) { - $this->useInterimHoldOffCaching = $enabled; - } - - /** - * @param int $flag ATTR_* class constant - * @return int QOS_* class constant - * @since 1.28 - */ - public function getQoS( $flag ) { - return $this->cache->getQoS( $flag ); - } - - /** - * Get a TTL that is higher for objects that have not changed recently - * - * This is useful for keys that get explicit purges and DB or purge relay - * lag is a potential concern (especially how it interacts with CDN cache) - * - * Example usage: - * @code - * // Last-modified time of page - * $mtime = wfTimestamp( TS_UNIX, $page->getTimestamp() ); - * // Get adjusted TTL. If $mtime is 3600 seconds ago and $minTTL/$factor left at - * // defaults, then $ttl is 3600 * .2 = 720. If $minTTL was greater than 720, then - * // $ttl would be $minTTL. If $maxTTL was smaller than 720, $ttl would be $maxTTL. - * $ttl = $cache->adaptiveTTL( $mtime, $cache::TTL_DAY ); - * @endcode - * - * Another use case is when there are no applicable "last modified" fields in the DB, - * and there are too many dependencies for explicit purges to be viable, and the rate of - * change to relevant content is unstable, and it is highly valued to have the cached value - * be as up-to-date as possible. - * - * Example usage: - * @code - * $query = ""; - * $idListFromComplexQuery = $cache->getWithSetCallback( - * $cache->makeKey( 'complex-graph-query', $hashOfQuery ), - * GraphQueryClass::STARTING_TTL, - * function ( $oldValue, &$ttl, array &$setOpts, $oldAsOf ) use ( $query, $cache ) { - * $gdb = $this->getReplicaGraphDbConnection(); - * // Account for any snapshot/replica DB lag - * $setOpts += GraphDatabase::getCacheSetOptions( $gdb ); - * - * $newList = iterator_to_array( $gdb->query( $query ) ); - * sort( $newList, SORT_NUMERIC ); // normalize - * - * $minTTL = GraphQueryClass::MIN_TTL; - * $maxTTL = GraphQueryClass::MAX_TTL; - * if ( $oldValue !== false ) { - * // Note that $oldAsOf is the last time this callback ran - * $ttl = ( $newList === $oldValue ) - * // No change: cache for 150% of the age of $oldValue - * ? $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, 1.5 ) - * // Changed: cache for 50% of the age of $oldValue - * : $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, .5 ); - * } - * - * return $newList; - * }, - * [ - * // Keep stale values around for doing comparisons for TTL calculations. - * // High values improve long-tail keys hit-rates, though might waste space. - * 'staleTTL' => GraphQueryClass::GRACE_TTL - * ] - * ); - * @endcode - * - * @param int|float $mtime UNIX timestamp - * @param int $maxTTL Maximum TTL (seconds) - * @param int $minTTL Minimum TTL (seconds); Default: 30 - * @param float $factor Value in the range (0,1); Default: .2 - * @return int Adaptive TTL - * @since 1.28 - */ - public function adaptiveTTL( $mtime, $maxTTL, $minTTL = 30, $factor = 0.2 ) { - if ( is_float( $mtime ) || ctype_digit( $mtime ) ) { - $mtime = (int)$mtime; // handle fractional seconds and string integers - } - - if ( !is_int( $mtime ) || $mtime <= 0 ) { - return $minTTL; // no last-modified time provided - } - - $age = $this->getCurrentTime() - $mtime; - - return (int)min( $maxTTL, max( $minTTL, $factor * $age ) ); - } - - /** - * @return int Number of warmup key cache misses last round - * @since 1.30 - */ - final public function getWarmupKeyMisses() { - return $this->warmupKeyMisses; - } - - /** - * Do the actual async bus purge of a key - * - * This must set the key to "PURGED::" - * - * @param string $key Cache key - * @param int $ttl Seconds to keep the tombstone around - * @param int $holdoff HOLDOFF_* constant controlling how long to ignore sets for this key - * @return bool Success - */ - protected function relayPurge( $key, $ttl, $holdoff ) { - if ( $this->mcrouterAware ) { - // See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup - // Wildcards select all matching routes, e.g. the WAN cluster on all DCs - $ok = $this->cache->set( - "/*/{$this->cluster}/{$key}", - $this->makePurgeValue( $this->getCurrentTime(), self::HOLDOFF_TTL_NONE ), - $ttl - ); - } else { - // This handles the mcrouter and the single-DC case - $ok = $this->cache->set( - $key, - $this->makePurgeValue( $this->getCurrentTime(), self::HOLDOFF_TTL_NONE ), - $ttl - ); - } - - return $ok; - } - - /** - * Do the actual async bus delete of a key - * - * @param string $key Cache key - * @return bool Success - */ - protected function relayDelete( $key ) { - if ( $this->mcrouterAware ) { - // See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup - // Wildcards select all matching routes, e.g. the WAN cluster on all DCs - $ok = $this->cache->delete( "/*/{$this->cluster}/{$key}" ); - } else { - // Some other proxy handles broadcasting or there is only one datacenter - $ok = $this->cache->delete( $key ); - } - - return $ok; - } - - /** - * @param string $key - * @param int $ttl Seconds to live - * @param callable $callback - * @param array $opts - * @return bool Success - * @note Callable type hints are not used to avoid class-autoloading - */ - private function scheduleAsyncRefresh( $key, $ttl, $callback, $opts ) { - if ( !$this->asyncHandler ) { - return false; - } - // Update the cache value later, such during post-send of an HTTP request - $func = $this->asyncHandler; - $func( function () use ( $key, $ttl, $callback, $opts ) { - $opts['minAsOf'] = INF; // force a refresh - $this->fetchOrRegenerate( $key, $ttl, $callback, $opts ); - } ); - - return true; - } - - /** - * Check if a key is fresh or in the grace window and thus due for randomized reuse - * - * If $curTTL > 0 (e.g. not expired) this returns true. Otherwise, the chance of returning - * true decrease steadily from 100% to 0% as the |$curTTL| moves from 0 to $graceTTL seconds. - * This handles widely varying levels of cache access traffic. - * - * If $curTTL <= -$graceTTL (e.g. already expired), then this returns false. - * - * @param float $curTTL Approximate TTL left on the key if present - * @param int $graceTTL Consider using stale values if $curTTL is greater than this - * @return bool - */ - private function isAliveOrInGracePeriod( $curTTL, $graceTTL ) { - if ( $curTTL > 0 ) { - return true; - } elseif ( $graceTTL <= 0 ) { - return false; - } - - $ageStale = abs( $curTTL ); // seconds of staleness - $curGTTL = ( $graceTTL - $ageStale ); // current grace-time-to-live - if ( $curGTTL <= 0 ) { - return false; // already out of grace period - } - - // Chance of using a stale value is the complement of the chance of refreshing it - return !$this->worthRefreshExpiring( $curGTTL, $graceTTL ); - } - - /** - * Check if a key is nearing expiration and thus due for randomized regeneration - * - * This returns false if $curTTL >= $lowTTL. Otherwise, the chance of returning true - * increases steadily from 0% to 100% as the $curTTL moves from $lowTTL to 0 seconds. - * This handles widely varying levels of cache access traffic. - * - * If $curTTL <= 0 (e.g. already expired), then this returns false. - * - * @param float $curTTL Approximate TTL left on the key if present - * @param float $lowTTL Consider a refresh when $curTTL is less than this - * @return bool - */ - protected function worthRefreshExpiring( $curTTL, $lowTTL ) { - if ( $lowTTL <= 0 ) { - return false; - } elseif ( $curTTL >= $lowTTL ) { - return false; - } elseif ( $curTTL <= 0 ) { - return false; - } - - $chance = ( 1 - $curTTL / $lowTTL ); - - return mt_rand( 1, 1e9 ) <= 1e9 * $chance; - } - - /** - * Check if a key is due for randomized regeneration due to its popularity - * - * This is used so that popular keys can preemptively refresh themselves for higher - * consistency (especially in the case of purge loss/delay). Unpopular keys can remain - * in cache with their high nominal TTL. This means popular keys keep good consistency, - * whether the data changes frequently or not, and long-tail keys get to stay in cache - * and get hits too. Similar to worthRefreshExpiring(), randomization is used. - * - * @param float $asOf UNIX timestamp of the value - * @param int $ageNew Age of key when this might recommend refreshing (seconds) - * @param int $timeTillRefresh Age of key when it should be refreshed if popular (seconds) - * @param float $now The current UNIX timestamp - * @return bool - */ - protected function worthRefreshPopular( $asOf, $ageNew, $timeTillRefresh, $now ) { - if ( $ageNew < 0 || $timeTillRefresh <= 0 ) { - return false; - } - - $age = $now - $asOf; - $timeOld = $age - $ageNew; - if ( $timeOld <= 0 ) { - return false; - } - - $popularHitsPerSec = 1; - // Lifecycle is: new, ramp-up refresh chance, full refresh chance. - // Note that the "expected # of refreshes" for the ramp-up time range is half - // of what it would be if P(refresh) was at its full value during that time range. - $refreshWindowSec = max( $timeTillRefresh - $ageNew - self::$RAMPUP_TTL / 2, 1 ); - // P(refresh) * (# hits in $refreshWindowSec) = (expected # of refreshes) - // P(refresh) * ($refreshWindowSec * $popularHitsPerSec) = 1 (by definition) - // P(refresh) = 1/($refreshWindowSec * $popularHitsPerSec) - $chance = 1 / ( $popularHitsPerSec * $refreshWindowSec ); - - // Ramp up $chance from 0 to its nominal value over RAMPUP_TTL seconds to avoid stampedes - $chance *= ( $timeOld <= self::$RAMPUP_TTL ) ? $timeOld / self::$RAMPUP_TTL : 1; - - return mt_rand( 1, 1e9 ) <= 1e9 * $chance; - } - - /** - * Check if $value is not false, versioned (if needed), and not older than $minTime (if set) - * - * @param array|bool $value - * @param float $asOf The time $value was generated - * @param float $minAsOf Minimum acceptable "as of" timestamp - * @param float|null $purgeTime The last time the value was invalidated - * @return bool - */ - protected function isValid( $value, $asOf, $minAsOf, $purgeTime = null ) { - // Avoid reading any key not generated after the latest delete() or touch - $safeMinAsOf = max( $minAsOf, $purgeTime + self::$TINY_POSTIVE ); - - if ( $value === false ) { - return false; - } elseif ( $safeMinAsOf > 0 && $asOf < $minAsOf ) { - return false; - } - - return true; - } - - /** - * @param mixed $value - * @param int $ttl Seconds to live or zero for "indefinite" - * @param int|null $version Value version number or null if not versioned - * @param float $now Unix Current timestamp just before calling set() - * @param float $walltime How long it took to generate the value in seconds - * @return array - */ - private function wrap( $value, $ttl, $version, $now, $walltime ) { - // Returns keys in ascending integer order for PHP7 array packing: - // https://nikic.github.io/2014/12/22/PHPs-new-hashtable-implementation.html - $wrapped = [ - self::$FLD_FORMAT_VERSION => self::$VERSION, - self::$FLD_VALUE => $value, - self::$FLD_TTL => $ttl, - self::$FLD_TIME => $now - ]; - if ( $version !== null ) { - $wrapped[self::$FLD_VALUE_VERSION] = $version; - } - if ( $walltime >= self::$GENERATION_SLOW_SEC ) { - $wrapped[self::$FLD_GENERATION_TIME] = $walltime; - } - - return $wrapped; - } - - /** - * @param array|string|bool $wrapped The entry at a cache key - * @param float $now Unix Current timestamp (preferrably pre-query) - * @return array (value or false if absent/tombstoned/malformed, value metadata map). - * The cache key metadata includes the following metadata: - * - asOf: UNIX timestamp of the value or null if there is no value - * - curTTL: remaining time-to-live (negative if tombstoned) or null if there is no value - * - version: value version number or null if the if there is no value - * - tombAsOf: UNIX timestamp of the tombstone or null if there is no tombstone - */ - private function unwrap( $wrapped, $now ) { - $value = false; - $info = [ 'asOf' => null, 'curTTL' => null, 'version' => null, 'tombAsOf' => null ]; - - if ( is_array( $wrapped ) ) { - // Entry expected to be a cached value; validate it - if ( - ( $wrapped[self::$FLD_FORMAT_VERSION] ?? null ) === self::$VERSION && - $wrapped[self::$FLD_TIME] >= $this->epoch - ) { - if ( $wrapped[self::$FLD_TTL] > 0 ) { - // Get the approximate time left on the key - $age = $now - $wrapped[self::$FLD_TIME]; - $curTTL = max( $wrapped[self::$FLD_TTL] - $age, 0.0 ); - } else { - // Key had no TTL, so the time left is unbounded - $curTTL = INF; - } - $value = $wrapped[self::$FLD_VALUE]; - $info['version'] = $wrapped[self::$FLD_VALUE_VERSION] ?? null; - $info['asOf'] = $wrapped[self::$FLD_TIME]; - $info['curTTL'] = $curTTL; - } - } else { - // Entry expected to be a tombstone; parse it - $purge = $this->parsePurgeValue( $wrapped ); - if ( $purge !== false ) { - // Tombstoned keys should always have a negative current $ttl - $info['curTTL'] = min( $purge[self::$PURGE_TIME] - $now, self::$TINY_NEGATIVE ); - $info['tombAsOf'] = $purge[self::$PURGE_TIME]; - } - } - - return [ $value, $info ]; - } - - /** - * @param string[] $keys - * @param string $prefix - * @return string[] Prefix keys; the order of $keys is preserved - */ - protected static function prefixCacheKeys( array $keys, $prefix ) { - $res = []; - foreach ( $keys as $key ) { - $res[] = $prefix . $key; - } - - return $res; - } - - /** - * @param string $key String of the format :[:]... - * @return string A collection name to describe this class of key - */ - private function determineKeyClassForStats( $key ) { - $parts = explode( ':', $key, 3 ); - - return $parts[1] ?? $parts[0]; // sanity - } - - /** - * @param string|array|bool $value Possible string of the form "PURGED::" - * @return array|bool Array containing a UNIX timestamp (float) and holdoff period (integer), - * or false if value isn't a valid purge value - */ - private function parsePurgeValue( $value ) { - if ( !is_string( $value ) ) { - return false; - } - - $segments = explode( ':', $value, 3 ); - if ( - !isset( $segments[0] ) || - !isset( $segments[1] ) || - "{$segments[0]}:" !== self::$PURGE_VAL_PREFIX - ) { - return false; - } - - if ( !isset( $segments[2] ) ) { - // Back-compat with old purge values without holdoff - $segments[2] = self::HOLDOFF_TTL; - } - - if ( $segments[1] < $this->epoch ) { - // Values this old are ignored - return false; - } - - return [ - self::$PURGE_TIME => (float)$segments[1], - self::$PURGE_HOLDOFF => (int)$segments[2], - ]; - } - - /** - * @param float $timestamp - * @param int $holdoff In seconds - * @return string Wrapped purge value - */ - private function makePurgeValue( $timestamp, $holdoff ) { - return self::$PURGE_VAL_PREFIX . (float)$timestamp . ':' . (int)$holdoff; - } - - /** - * @param string $group - * @return MapCacheLRU - */ - private function getProcessCache( $group ) { - if ( !isset( $this->processCaches[$group] ) ) { - list( , $size ) = explode( ':', $group ); - $this->processCaches[$group] = new MapCacheLRU( (int)$size ); - } - - return $this->processCaches[$group]; - } - - /** - * @param string $key - * @param int $version - * @return string - */ - private function getProcessCacheKey( $key, $version ) { - return $key . ' ' . (int)$version; - } - - /** - * @param ArrayIterator $keys - * @param array $opts - * @return string[] Map of (ID => cache key) - */ - private function getNonProcessCachedMultiKeys( ArrayIterator $keys, array $opts ) { - $pcTTL = $opts['pcTTL'] ?? self::TTL_UNCACHEABLE; - - $keysMissing = []; - if ( $pcTTL > 0 && $this->callbackDepth == 0 ) { - $version = $opts['version'] ?? null; - $pCache = $this->getProcessCache( $opts['pcGroup'] ?? self::PC_PRIMARY ); - foreach ( $keys as $key => $id ) { - if ( !$pCache->has( $this->getProcessCacheKey( $key, $version ), $pcTTL ) ) { - $keysMissing[$id] = $key; - } - } - } - - return $keysMissing; - } - - /** - * @param string[] $keys - * @param string[]|string[][] $checkKeys - * @return string[] List of cache keys - */ - private function getRawKeysForWarmup( array $keys, array $checkKeys ) { - if ( !$keys ) { - return []; - } - - $keysWarmUp = []; - // Get all the value keys to fetch... - foreach ( $keys as $key ) { - $keysWarmUp[] = self::$VALUE_KEY_PREFIX . $key; - } - // Get all the check keys to fetch... - foreach ( $checkKeys as $i => $checkKeyOrKeys ) { - if ( is_int( $i ) ) { - // Single check key that applies to all value keys - $keysWarmUp[] = self::$TIME_KEY_PREFIX . $checkKeyOrKeys; - } else { - // List of check keys that apply to value key $i - $keysWarmUp = array_merge( - $keysWarmUp, - self::prefixCacheKeys( $checkKeyOrKeys, self::$TIME_KEY_PREFIX ) - ); - } - } - - $warmupCache = $this->cache->getMulti( $keysWarmUp ); - $warmupCache += array_fill_keys( $keysWarmUp, false ); - - return $warmupCache; - } - - /** - * @return float UNIX timestamp - * @codeCoverageIgnore - */ - protected function getCurrentTime() { - if ( $this->wallClockOverride ) { - return $this->wallClockOverride; - } - - $clockTime = (float)time(); // call this first - // microtime() uses an initial gettimeofday() call added to usage clocks. - // This can severely drift from time() and the microtime() value of other threads - // due to undercounting of the amount of time elapsed. Instead of seeing the current - // time as being in the past, use the value of time(). This avoids setting cache values - // that will immediately be seen as expired and possibly cause stampedes. - return max( microtime( true ), $clockTime ); - } - - /** - * @param float|null &$time Mock UNIX timestamp for testing - * @codeCoverageIgnore - */ - public function setMockTime( &$time ) { - $this->wallClockOverride =& $time; - $this->cache->setMockTime( $time ); - } -} diff --git a/includes/libs/objectcache/WinCacheBagOStuff.php b/includes/libs/objectcache/WinCacheBagOStuff.php new file mode 100644 index 0000000000..0e4e3fb63d --- /dev/null +++ b/includes/libs/objectcache/WinCacheBagOStuff.php @@ -0,0 +1,158 @@ +unserialize( $blob ); + if ( $value !== false ) { + $casToken = (string)$blob; // don't bother hashing this + } + + return $value; + } + + protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) { + if ( !wincache_lock( $key ) ) { // optimize with FIFO lock + return false; + } + + $curCasToken = null; // passed by reference + $this->doGet( $key, self::READ_LATEST, $curCasToken ); + if ( $casToken === $curCasToken ) { + $success = $this->set( $key, $value, $exptime, $flags ); + } else { + $this->logger->info( + __METHOD__ . ' failed due to race condition for {key}.', + [ 'key' => $key ] + ); + + $success = false; // mismatched or failed + } + + wincache_unlock( $key ); + + return $success; + } + + protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) { + $result = wincache_ucache_set( $key, $this->serialize( $value ), $exptime ); + + // false positive, wincache_ucache_set returns an empty array + // in some circumstances. + // @phan-suppress-next-line PhanTypeComparisonToArray + return ( $result === [] || $result === true ); + } + + public function add( $key, $value, $exptime = 0, $flags = 0 ) { + if ( wincache_ucache_exists( $key ) ) { + return false; // avoid warnings + } + + $result = wincache_ucache_add( $key, $this->serialize( $value ), $exptime ); + + // false positive, wincache_ucache_add returns an empty array + // in some circumstances. + // @phan-suppress-next-line PhanTypeComparisonToArray + return ( $result === [] || $result === true ); + } + + protected function doDelete( $key, $flags = 0 ) { + wincache_ucache_delete( $key ); + + return true; + } + + /** + * Construct a cache key. + * + * @since 1.27 + * @param string $keyspace + * @param array $args + * @return string + */ + public function makeKeyInternal( $keyspace, $args ) { + // WinCache keys have a maximum length of 150 characters. From that, + // subtract the number of characters we need for the keyspace and for + // the separator character needed for each argument. To handle some + // custom prefixes used by thing like WANObjectCache, limit to 125. + // NOTE: Same as in memcached, except the max key length there is 255. + $charsLeft = 125 - strlen( $keyspace ) - count( $args ); + + $args = array_map( + function ( $arg ) use ( &$charsLeft ) { + // 33 = 32 characters for the MD5 + 1 for the '#' prefix. + if ( $charsLeft > 33 && strlen( $arg ) > $charsLeft ) { + $arg = '#' . md5( $arg ); + } + + $charsLeft -= strlen( $arg ); + return $arg; + }, + $args + ); + + if ( $charsLeft < 0 ) { + return $keyspace . ':BagOStuff-long-key:##' . md5( implode( ':', $args ) ); + } + + return $keyspace . ':' . implode( ':', $args ); + } + + /** + * Increase stored value of $key by $value while preserving its original TTL + * @param string $key Key to increase + * @param int $value Value to add to $key (Default 1) + * @return int|bool New value or false on failure + */ + public function incr( $key, $value = 1 ) { + if ( !wincache_lock( $key ) ) { // optimize with FIFO lock + return false; + } + + $n = $this->doGet( $key ); + if ( $this->isInteger( $n ) ) { + $n = max( $n + (int)$value, 0 ); + $oldTTL = wincache_ucache_info( false, $key )["ucache_entries"][1]["ttl_seconds"]; + $this->set( $key, $n, $oldTTL ); + } else { + $n = false; + } + + wincache_unlock( $key ); + + return $n; + } +} diff --git a/includes/libs/objectcache/wancache/WANObjectCache.php b/includes/libs/objectcache/wancache/WANObjectCache.php new file mode 100644 index 0000000000..1852685d6c --- /dev/null +++ b/includes/libs/objectcache/wancache/WANObjectCache.php @@ -0,0 +1,2633 @@ += 0 due to clock skew */ + private static $TINY_NEGATIVE = -0.000001; + /** @var float Tiny positive float to use when using "minTime" to assert an inequality */ + private static $TINY_POSTIVE = 0.000001; + + /** @var int Milliseconds of key fetch/validate/regenerate delay prone to set() stampedes */ + private static $SET_DELAY_HIGH_MS = 50; + /** @var int Min millisecond set() backoff during hold-off (far less than INTERIM_KEY_TTL) */ + private static $RECENT_SET_LOW_MS = 50; + /** @var int Max millisecond set() backoff during hold-off (far less than INTERIM_KEY_TTL) */ + private static $RECENT_SET_HIGH_MS = 100; + + /** @var int Consider value generation slow if it takes more than this many seconds */ + private static $GENERATION_SLOW_SEC = 3; + + /** @var int Key to the tombstone entry timestamp */ + private static $PURGE_TIME = 0; + /** @var int Key to the tombstone entry hold-off TTL */ + private static $PURGE_HOLDOFF = 1; + + /** @var int Cache format version number */ + private static $VERSION = 1; + + /** @var int Key to WAN cache version number */ + private static $FLD_FORMAT_VERSION = 0; + /** @var int Key to the cached value */ + private static $FLD_VALUE = 1; + /** @var int Key to the original TTL */ + private static $FLD_TTL = 2; + /** @var int Key to the cache timestamp */ + private static $FLD_TIME = 3; + /** @var int Key to the flags bit field (reserved number) */ + private static /** @noinspection PhpUnusedPrivateFieldInspection */ $FLD_FLAGS = 4; + /** @var int Key to collection cache version number */ + private static $FLD_VALUE_VERSION = 5; + /** @var int Key to how long it took to generate the value */ + private static $FLD_GENERATION_TIME = 6; + + private static $VALUE_KEY_PREFIX = 'WANCache:v:'; + private static $INTERIM_KEY_PREFIX = 'WANCache:i:'; + private static $TIME_KEY_PREFIX = 'WANCache:t:'; + private static $MUTEX_KEY_PREFIX = 'WANCache:m:'; + private static $COOLOFF_KEY_PREFIX = 'WANCache:c:'; + + private static $PURGE_VAL_PREFIX = 'PURGED:'; + + /** + * @param array $params + * - cache : BagOStuff object for a persistent cache + * - logger : LoggerInterface object + * - stats : StatsdDataFactoryInterface object + * - asyncHandler : A function that takes a callback and runs it later. If supplied, + * whenever a preemptive refresh would be triggered in getWithSetCallback(), the + * current cache value is still used instead. However, the async-handler function + * receives a WAN cache callback that, when run, will execute the value generation + * callback supplied by the getWithSetCallback() caller. The result will be saved + * as normal. The handler is expected to call the WAN cache callback at an opportune + * time (e.g. HTTP post-send), though generally within a few 100ms. [optional] + * - region: the current physical region. This is required when using mcrouter as the + * backing store proxy. [optional] + * - cluster: name of the cache cluster used by this WAN cache. The name must be the + * same in all datacenters; the ("region","cluster") tuple is what distinguishes + * the counterpart cache clusters among all the datacenter. The contents of + * https://github.com/facebook/mcrouter/wiki/Config-Files give background on this. + * This is required when using mcrouter as the backing store proxy. [optional] + * - mcrouterAware: set as true if mcrouter is the backing store proxy and mcrouter + * is configured to interpret /// key prefixes as routes. This + * requires that "region" and "cluster" are both set above. [optional] + * - epoch: lowest UNIX timestamp a value/tombstone must have to be valid. [optional] + * - secret: stable secret used for hashing long strings into key components. [optional] + */ + public function __construct( array $params ) { + $this->cache = $params['cache']; + $this->region = $params['region'] ?? 'main'; + $this->cluster = $params['cluster'] ?? 'wan-main'; + $this->mcrouterAware = !empty( $params['mcrouterAware'] ); + $this->epoch = $params['epoch'] ?? 0; + $this->secret = $params['secret'] ?? (string)$this->epoch; + + $this->setLogger( $params['logger'] ?? new NullLogger() ); + $this->stats = $params['stats'] ?? new NullStatsdDataFactory(); + $this->asyncHandler = $params['asyncHandler'] ?? null; + } + + /** + * @param LoggerInterface $logger + */ + public function setLogger( LoggerInterface $logger ) { + $this->logger = $logger; + } + + /** + * Get an instance that wraps EmptyBagOStuff + * + * @return WANObjectCache + */ + public static function newEmpty() { + return new static( [ 'cache' => new EmptyBagOStuff() ] ); + } + + /** + * Fetch the value of a key from cache + * + * If supplied, $curTTL is set to the remaining TTL (current time left): + * - a) INF; if $key exists, has no TTL, and is not invalidated by $checkKeys + * - b) float (>=0); if $key exists, has a TTL, and is not invalidated by $checkKeys + * - c) float (<0); if $key is tombstoned, stale, or existing but invalidated by $checkKeys + * - d) null; if $key does not exist and is not tombstoned + * + * If a key is tombstoned, $curTTL will reflect the time since delete(). + * + * The timestamp of $key will be checked against the last-purge timestamp + * of each of $checkKeys. Those $checkKeys not in cache will have the last-purge + * initialized to the current timestamp. If any of $checkKeys have a timestamp + * greater than that of $key, then $curTTL will reflect how long ago $key + * became invalid. Callers can use $curTTL to know when the value is stale. + * The $checkKeys parameter allow mass invalidations by updating a single key: + * - a) Each "check" key represents "last purged" of some source data + * - b) Callers pass in relevant "check" keys as $checkKeys in get() + * - c) When the source data that "check" keys represent changes, + * the touchCheckKey() method is called on them + * + * Source data entities might exists in a DB that uses snapshot isolation + * (e.g. the default REPEATABLE-READ in innoDB). Even for mutable data, that + * isolation can largely be maintained by doing the following: + * - a) Calling delete() on entity change *and* creation, before DB commit + * - b) Keeping transaction duration shorter than the delete() hold-off TTL + * - c) Disabling interim key caching via useInterimHoldOffCaching() before get() calls + * + * However, pre-snapshot values might still be seen if an update was made + * in a remote datacenter but the purge from delete() didn't relay yet. + * + * Consider using getWithSetCallback() instead of get() and set() cycles. + * That method has cache slam avoiding features for hot/expensive keys. + * + * Pass $info as WANObjectCache::PASS_BY_REF to transform it into a cache key metadata map. + * This map includes the following metadata: + * - asOf: UNIX timestamp of the value or null if the key is nonexistant + * - tombAsOf: UNIX timestamp of the tombstone or null if the key is not tombstoned + * - lastCKPurge: UNIX timestamp of the highest check key or null if none provided + * - version: cached value version number or null if the key is nonexistant + * + * Otherwise, $info will transform into the cached value timestamp. + * + * @param string $key Cache key made from makeKey() or makeGlobalKey() + * @param mixed|null &$curTTL Approximate TTL left on the key if present/tombstoned [returned] + * @param string[] $checkKeys The "check" keys used to validate the value + * @param mixed|null &$info Key info if WANObjectCache::PASS_BY_REF [returned] + * @return mixed Value of cache key or false on failure + */ + final public function get( + $key, &$curTTL = null, array $checkKeys = [], &$info = null + ) { + $curTTLs = self::PASS_BY_REF; + $infoByKey = self::PASS_BY_REF; + $values = $this->getMulti( [ $key ], $curTTLs, $checkKeys, $infoByKey ); + $curTTL = $curTTLs[$key] ?? null; + if ( $info === self::PASS_BY_REF ) { + $info = [ + 'asOf' => $infoByKey[$key]['asOf'] ?? null, + 'tombAsOf' => $infoByKey[$key]['tombAsOf'] ?? null, + 'lastCKPurge' => $infoByKey[$key]['lastCKPurge'] ?? null, + 'version' => $infoByKey[$key]['version'] ?? null + ]; + } else { + $info = $infoByKey[$key]['asOf'] ?? null; // b/c + } + + return $values[$key] ?? false; + } + + /** + * Fetch the value of several keys from cache + * + * Pass $info as WANObjectCache::PASS_BY_REF to transform it into a map of cache keys + * to cache key metadata maps, each having the same style as those of WANObjectCache::get(). + * All the cache keys listed in $keys will have an entry. + * + * Othwerwise, $info will transform into a map of (cache key => cached value timestamp). + * Only the cache keys listed in $keys that exists or are tombstoned will have an entry. + * + * $checkKeys holds the "check" keys used to validate values of applicable keys. The integer + * indexes hold "check" keys that apply to all of $keys while the string indexes hold "check" + * keys that only apply to the cache key with that name. + * + * @see WANObjectCache::get() + * + * @param string[] $keys List of cache keys made from makeKey() or makeGlobalKey() + * @param mixed|null &$curTTLs Map of (key => TTL left) for existing/tombstoned keys [returned] + * @param string[]|string[][] $checkKeys Map of (integer or cache key => "check" key(s)) + * @param mixed|null &$info Map of (key => info) if WANObjectCache::PASS_BY_REF [returned] + * @return mixed[] Map of (key => value) for existing values; order of $keys is preserved + */ + final public function getMulti( + array $keys, + &$curTTLs = [], + array $checkKeys = [], + &$info = null + ) { + $result = []; + $curTTLs = []; + $infoByKey = []; + + $vPrefixLen = strlen( self::$VALUE_KEY_PREFIX ); + $valueKeys = self::prefixCacheKeys( $keys, self::$VALUE_KEY_PREFIX ); + + $checkKeysForAll = []; + $checkKeysByKey = []; + $checkKeysFlat = []; + foreach ( $checkKeys as $i => $checkKeyGroup ) { + $prefixed = self::prefixCacheKeys( (array)$checkKeyGroup, self::$TIME_KEY_PREFIX ); + $checkKeysFlat = array_merge( $checkKeysFlat, $prefixed ); + // Are these check keys for a specific cache key, or for all keys being fetched? + if ( is_int( $i ) ) { + $checkKeysForAll = array_merge( $checkKeysForAll, $prefixed ); + } else { + $checkKeysByKey[$i] = $prefixed; + } + } + + // Fetch all of the raw values + $keysGet = array_merge( $valueKeys, $checkKeysFlat ); + if ( $this->warmupCache ) { + $wrappedValues = array_intersect_key( $this->warmupCache, array_flip( $keysGet ) ); + $keysGet = array_diff( $keysGet, array_keys( $wrappedValues ) ); // keys left to fetch + $this->warmupKeyMisses += count( $keysGet ); + } else { + $wrappedValues = []; + } + if ( $keysGet ) { + $wrappedValues += $this->cache->getMulti( $keysGet ); + } + // Time used to compare/init "check" keys (derived after getMulti() to be pessimistic) + $now = $this->getCurrentTime(); + + // Collect timestamps from all "check" keys + $purgeValuesForAll = $this->processCheckKeys( $checkKeysForAll, $wrappedValues, $now ); + $purgeValuesByKey = []; + foreach ( $checkKeysByKey as $cacheKey => $checks ) { + $purgeValuesByKey[$cacheKey] = + $this->processCheckKeys( $checks, $wrappedValues, $now ); + } + + // Get the main cache value for each key and validate them + foreach ( $valueKeys as $vKey ) { + $key = substr( $vKey, $vPrefixLen ); // unprefix + list( $value, $keyInfo ) = $this->unwrap( $wrappedValues[$vKey] ?? false, $now ); + // Force dependent keys to be seen as stale for a while after purging + // to reduce race conditions involving stale data getting cached + $purgeValues = $purgeValuesForAll; + if ( isset( $purgeValuesByKey[$key] ) ) { + $purgeValues = array_merge( $purgeValues, $purgeValuesByKey[$key] ); + } + + $lastCKPurge = null; // timestamp of the highest check key + foreach ( $purgeValues as $purge ) { + $lastCKPurge = max( $purge[self::$PURGE_TIME], $lastCKPurge ); + $safeTimestamp = $purge[self::$PURGE_TIME] + $purge[self::$PURGE_HOLDOFF]; + if ( $value !== false && $safeTimestamp >= $keyInfo['asOf'] ) { + // How long ago this value was invalidated by *this* check key + $ago = min( $purge[self::$PURGE_TIME] - $now, self::$TINY_NEGATIVE ); + // How long ago this value was invalidated by *any* known check key + $keyInfo['curTTL'] = min( $keyInfo['curTTL'], $ago ); + } + } + $keyInfo[ 'lastCKPurge'] = $lastCKPurge; + + if ( $value !== false ) { + $result[$key] = $value; + } + if ( $keyInfo['curTTL'] !== null ) { + $curTTLs[$key] = $keyInfo['curTTL']; + } + + $infoByKey[$key] = ( $info === self::PASS_BY_REF ) + ? $keyInfo + : $keyInfo['asOf']; // b/c + } + + $info = $infoByKey; + + return $result; + } + + /** + * @since 1.27 + * @param string[] $timeKeys List of prefixed time check keys + * @param mixed[] $wrappedValues + * @param float $now + * @return array[] List of purge value arrays + */ + private function processCheckKeys( array $timeKeys, array $wrappedValues, $now ) { + $purgeValues = []; + foreach ( $timeKeys as $timeKey ) { + $purge = isset( $wrappedValues[$timeKey] ) + ? $this->parsePurgeValue( $wrappedValues[$timeKey] ) + : false; + if ( $purge === false ) { + // Key is not set or malformed; regenerate + $newVal = $this->makePurgeValue( $now, self::HOLDOFF_TTL ); + $this->cache->add( $timeKey, $newVal, self::$CHECK_KEY_TTL ); + $purge = $this->parsePurgeValue( $newVal ); + } + $purgeValues[] = $purge; + } + return $purgeValues; + } + + /** + * Set the value of a key in cache + * + * Simply calling this method when source data changes is not valid because + * the changes do not replicate to the other WAN sites. In that case, delete() + * should be used instead. This method is intended for use on cache misses. + * + * If the data was read from a snapshot-isolated transactions (e.g. the default + * REPEATABLE-READ in innoDB), use 'since' to avoid the following race condition: + * - a) T1 starts + * - b) T2 updates a row, calls delete(), and commits + * - c) The HOLDOFF_TTL passes, expiring the delete() tombstone + * - d) T1 reads the row and calls set() due to a cache miss + * - e) Stale value is stuck in cache + * + * Setting 'lag' and 'since' help avoids keys getting stuck in stale states. + * + * Be aware that this does not update the process cache for getWithSetCallback() + * callers. Keys accessed via that method are not generally meant to also be set + * using this primitive method. + * + * Do not use this method on versioned keys accessed via getWithSetCallback(). + * + * Example usage: + * @code + * $dbr = wfGetDB( DB_REPLICA ); + * $setOpts = Database::getCacheSetOptions( $dbr ); + * // Fetch the row from the DB + * $row = $dbr->selectRow( ... ); + * $key = $cache->makeKey( 'building', $buildingId ); + * $cache->set( $key, $row, $cache::TTL_DAY, $setOpts ); + * @endcode + * + * @param string $key Cache key + * @param mixed $value + * @param int $ttl Seconds to live. Special values are: + * - WANObjectCache::TTL_INDEFINITE: Cache forever (default) + * - WANObjectCache::TTL_UNCACHEABLE: Do not cache (if the key exists, it is not deleted) + * @param array $opts Options map: + * - lag: Seconds of replica DB lag. Typically, this is either the replica DB lag + * before the data was read or, if applicable, the replica DB lag before + * the snapshot-isolated transaction the data was read from started. + * Use false to indicate that replication is not running. + * Default: 0 seconds + * - since: UNIX timestamp of the data in $value. Typically, this is either + * the current time the data was read or (if applicable) the time when + * the snapshot-isolated transaction the data was read from started. + * Default: 0 seconds + * - pending: Whether this data is possibly from an uncommitted write transaction. + * Generally, other threads should not see values from the future and + * they certainly should not see ones that ended up getting rolled back. + * Default: false + * - lockTSE: If excessive replication/snapshot lag is detected, then store the value + * with this TTL and flag it as stale. This is only useful if the reads for this key + * use getWithSetCallback() with "lockTSE" set. Note that if "staleTTL" is set + * then it will still add on to this TTL in the excessive lag scenario. + * Default: WANObjectCache::TSE_NONE + * - staleTTL: Seconds to keep the key around if it is stale. The get()/getMulti() + * methods return such stale values with a $curTTL of 0, and getWithSetCallback() + * will call the regeneration callback in such cases, passing in the old value + * and its as-of time to the callback. This is useful if adaptiveTTL() is used + * on the old value's as-of time when it is verified as still being correct. + * Default: WANObjectCache::STALE_TTL_NONE + * - creating: Optimize for the case where the key does not already exist. + * Default: false + * - version: Integer version number signifiying the format of the value. + * Default: null + * - walltime: How long the value took to generate in seconds. Default: 0.0 + * @note Options added in 1.28: staleTTL + * @note Options added in 1.33: creating + * @note Options added in 1.34: version, walltime + * @return bool Success + */ + final public function set( $key, $value, $ttl = self::TTL_INDEFINITE, array $opts = [] ) { + $now = $this->getCurrentTime(); + $lag = $opts['lag'] ?? 0; + $age = isset( $opts['since'] ) ? max( 0, $now - $opts['since'] ) : 0; + $pending = $opts['pending'] ?? false; + $lockTSE = $opts['lockTSE'] ?? self::TSE_NONE; + $staleTTL = $opts['staleTTL'] ?? self::STALE_TTL_NONE; + $creating = $opts['creating'] ?? false; + $version = $opts['version'] ?? null; + $walltime = $opts['walltime'] ?? 0.0; + + if ( $ttl < 0 ) { + return true; + } + + // Do not cache potentially uncommitted data as it might get rolled back + if ( $pending ) { + $this->logger->info( + 'Rejected set() for {cachekey} due to pending writes.', + [ 'cachekey' => $key ] + ); + + return true; // no-op the write for being unsafe + } + + $logicalTTL = null; // logical TTL override + // Check if there's a risk of writing stale data after the purge tombstone expired + if ( $lag === false || ( $lag + $age ) > self::MAX_READ_LAG ) { + // Case A: any long-running transaction + if ( $age > self::MAX_READ_LAG ) { + if ( $lockTSE >= 0 ) { + // Store value as *almost* stale to avoid cache and mutex stampedes + $logicalTTL = self::TTL_SECOND; + $this->logger->info( + 'Lowered set() TTL for {cachekey} due to snapshot lag.', + [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] + ); + } else { + $this->logger->info( + 'Rejected set() for {cachekey} due to snapshot lag.', + [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] + ); + + return true; // no-op the write for being unsafe + } + // Case B: high replication lag; lower TTL instead of ignoring all set()s + } elseif ( $lag === false || $lag > self::MAX_READ_LAG ) { + if ( $lockTSE >= 0 ) { + $logicalTTL = min( $ttl ?: INF, self::TTL_LAGGED ); + } else { + $ttl = min( $ttl ?: INF, self::TTL_LAGGED ); + } + $this->logger->warning( + 'Lowered set() TTL for {cachekey} due to replication lag.', + [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] + ); + // Case C: medium length request with medium replication lag + } elseif ( $lockTSE >= 0 ) { + // Store value as *almost* stale to avoid cache and mutex stampedes + $logicalTTL = self::TTL_SECOND; + $this->logger->info( + 'Lowered set() TTL for {cachekey} due to high read lag.', + [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] + ); + } else { + $this->logger->info( + 'Rejected set() for {cachekey} due to high read lag.', + [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] + ); + + return true; // no-op the write for being unsafe + } + } + + // Wrap that value with time/TTL/version metadata + $wrapped = $this->wrap( $value, $logicalTTL ?: $ttl, $version, $now, $walltime ); + $storeTTL = $ttl + $staleTTL; + + if ( $creating ) { + $ok = $this->cache->add( self::$VALUE_KEY_PREFIX . $key, $wrapped, $storeTTL ); + } else { + $ok = $this->cache->merge( + self::$VALUE_KEY_PREFIX . $key, + function ( $cache, $key, $cWrapped ) use ( $wrapped ) { + // A string value means that it is a tombstone; do nothing in that case + return ( is_string( $cWrapped ) ) ? false : $wrapped; + }, + $storeTTL, + 1 // 1 attempt + ); + } + + return $ok; + } + + /** + * Purge a key from all datacenters + * + * This should only be called when the underlying data (being cached) + * changes in a significant way. This deletes the key and starts a hold-off + * period where the key cannot be written to for a few seconds (HOLDOFF_TTL). + * This is done to avoid the following race condition: + * - a) Some DB data changes and delete() is called on a corresponding key + * - b) A request refills the key with a stale value from a lagged DB + * - c) The stale value is stuck there until the key is expired/evicted + * + * This is implemented by storing a special "tombstone" value at the cache + * key that this class recognizes; get() calls will return false for the key + * and any set() calls will refuse to replace tombstone values at the key. + * For this to always avoid stale value writes, the following must hold: + * - a) Replication lag is bounded to being less than HOLDOFF_TTL; or + * - b) If lag is higher, the DB will have gone into read-only mode already + * + * Note that set() can also be lag-aware and lower the TTL if it's high. + * + * Be aware that this does not clear the process cache. Even if it did, callbacks + * used by getWithSetCallback() might still return stale data in the case of either + * uncommitted or not-yet-replicated changes (callback generally use replica DBs). + * + * When using potentially long-running ACID transactions, a good pattern is + * to use a pre-commit hook to issue the delete. This means that immediately + * after commit, callers will see the tombstone in cache upon purge relay. + * It also avoids the following race condition: + * - a) T1 begins, changes a row, and calls delete() + * - b) The HOLDOFF_TTL passes, expiring the delete() tombstone + * - c) T2 starts, reads the row and calls set() due to a cache miss + * - d) T1 finally commits + * - e) Stale value is stuck in cache + * + * Example usage: + * @code + * $dbw->startAtomic( __METHOD__ ); // start of request + * ... ... + * // Update the row in the DB + * $dbw->update( ... ); + * $key = $cache->makeKey( 'homes', $homeId ); + * // Purge the corresponding cache entry just before committing + * $dbw->onTransactionPreCommitOrIdle( function() use ( $cache, $key ) { + * $cache->delete( $key ); + * } ); + * ... ... + * $dbw->endAtomic( __METHOD__ ); // end of request + * @endcode + * + * The $ttl parameter can be used when purging values that have not actually changed + * recently. For example, a cleanup script to purge cache entries does not really need + * a hold-off period, so it can use HOLDOFF_TTL_NONE. Likewise for user-requested purge. + * Note that $ttl limits the effective range of 'lockTSE' for getWithSetCallback(). + * + * If called twice on the same key, then the last hold-off TTL takes precedence. For + * idempotence, the $ttl should not vary for different delete() calls on the same key. + * + * @param string $key Cache key + * @param int $ttl Tombstone TTL; Default: WANObjectCache::HOLDOFF_TTL + * @return bool True if the item was purged or not found, false on failure + */ + final public function delete( $key, $ttl = self::HOLDOFF_TTL ) { + if ( $ttl <= 0 ) { + // Publish the purge to all datacenters + $ok = $this->relayDelete( self::$VALUE_KEY_PREFIX . $key ); + } else { + // Publish the purge to all datacenters + $ok = $this->relayPurge( self::$VALUE_KEY_PREFIX . $key, $ttl, self::HOLDOFF_TTL_NONE ); + } + + $kClass = $this->determineKeyClassForStats( $key ); + $this->stats->increment( "wanobjectcache.$kClass.delete." . ( $ok ? 'ok' : 'error' ) ); + + return $ok; + } + + /** + * Fetch the value of a timestamp "check" key + * + * The key will be *initialized* to the current time if not set, + * so only call this method if this behavior is actually desired + * + * The timestamp can be used to check whether a cached value is valid. + * Callers should not assume that this returns the same timestamp in + * all datacenters due to relay delays. + * + * The level of staleness can roughly be estimated from this key, but + * if the key was evicted from cache, such calculations may show the + * time since expiry as ~0 seconds. + * + * Note that "check" keys won't collide with other regular keys. + * + * @param string $key + * @return float UNIX timestamp + */ + final public function getCheckKeyTime( $key ) { + return $this->getMultiCheckKeyTime( [ $key ] )[$key]; + } + + /** + * Fetch the values of each timestamp "check" key + * + * This works like getCheckKeyTime() except it takes a list of keys + * and returns a map of timestamps instead of just that of one key + * + * This might be useful if both: + * - a) a class of entities each depend on hundreds of other entities + * - b) these other entities are depended upon by millions of entities + * + * The later entities can each use a "check" key to invalidate their dependee entities. + * However, it is expensive for the former entities to verify against all of the relevant + * "check" keys during each getWithSetCallback() call. A less expensive approach is to do + * these verifications only after a "time-till-verify" (TTV) has passed. This is a middle + * ground between using blind TTLs and using constant verification. The adaptiveTTL() method + * can be used to dynamically adjust the TTV. Also, the initial TTV can make use of the + * last-modified times of the dependant entities (either from the DB or the "check" keys). + * + * Example usage: + * @code + * $value = $cache->getWithSetCallback( + * $cache->makeGlobalKey( 'wikibase-item', $id ), + * self::INITIAL_TTV, // initial time-till-verify + * function ( $oldValue, &$ttv, &$setOpts, $oldAsOf ) use ( $checkKeys, $cache ) { + * $now = microtime( true ); + * // Use $oldValue if it passes max ultimate age and "check" key comparisons + * if ( $oldValue && + * $oldAsOf > max( $cache->getMultiCheckKeyTime( $checkKeys ) ) && + * ( $now - $oldValue['ctime'] ) <= self::MAX_CACHE_AGE + * ) { + * // Increase time-till-verify by 50% of last time to reduce overhead + * $ttv = $cache->adaptiveTTL( $oldAsOf, self::MAX_TTV, self::MIN_TTV, 1.5 ); + * // Unlike $oldAsOf, "ctime" is the ultimate age of the cached data + * return $oldValue; + * } + * + * $mtimes = []; // dependency last-modified times; passed by reference + * $value = [ 'data' => $this->fetchEntityData( $mtimes ), 'ctime' => $now ]; + * // Guess time-till-change among the dependencies, e.g. 1/(total change rate) + * $ttc = 1 / array_sum( array_map( + * function ( $mtime ) use ( $now ) { + * return 1 / ( $mtime ? ( $now - $mtime ) : 900 ); + * }, + * $mtimes + * ) ); + * // The time-to-verify should not be overly pessimistic nor optimistic + * $ttv = min( max( $ttc, self::MIN_TTV ), self::MAX_TTV ); + * + * return $value; + * }, + * [ 'staleTTL' => $cache::TTL_DAY ] // keep around to verify and re-save + * ); + * @endcode + * + * @see WANObjectCache::getCheckKeyTime() + * @see WANObjectCache::getWithSetCallback() + * + * @param string[] $keys + * @return float[] Map of (key => UNIX timestamp) + * @since 1.31 + */ + final public function getMultiCheckKeyTime( array $keys ) { + $rawKeys = []; + foreach ( $keys as $key ) { + $rawKeys[$key] = self::$TIME_KEY_PREFIX . $key; + } + + $rawValues = $this->cache->getMulti( $rawKeys ); + $rawValues += array_fill_keys( $rawKeys, false ); + + $times = []; + foreach ( $rawKeys as $key => $rawKey ) { + $purge = $this->parsePurgeValue( $rawValues[$rawKey] ); + if ( $purge !== false ) { + $time = $purge[self::$PURGE_TIME]; + } else { + // Casting assures identical floats for the next getCheckKeyTime() calls + $now = (string)$this->getCurrentTime(); + $this->cache->add( + $rawKey, + $this->makePurgeValue( $now, self::HOLDOFF_TTL ), + self::$CHECK_KEY_TTL + ); + $time = (float)$now; + } + + $times[$key] = $time; + } + + return $times; + } + + /** + * Purge a "check" key from all datacenters, invalidating keys that use it + * + * This should only be called when the underlying data (being cached) + * changes in a significant way, and it is impractical to call delete() + * on all keys that should be changed. When get() is called on those + * keys, the relevant "check" keys must be supplied for this to work. + * + * The "check" key essentially represents a last-modified time of an entity. + * When the key is touched, the timestamp will be updated to the current time. + * Keys using the "check" key via get(), getMulti(), or getWithSetCallback() will + * be invalidated. This approach is useful if many keys depend on a single entity. + * + * The timestamp of the "check" key is treated as being HOLDOFF_TTL seconds in the + * future by get*() methods in order to avoid race conditions where keys are updated + * with stale values (e.g. from a lagged replica DB). A high TTL is set on the "check" + * key, making it possible to know the timestamp of the last change to the corresponding + * entities in most cases. This might use more cache space than resetCheckKey(). + * + * When a few important keys get a large number of hits, a high cache time is usually + * desired as well as "lockTSE" logic. The resetCheckKey() method is less appropriate + * in such cases since the "time since expiry" cannot be inferred, causing any get() + * after the reset to treat the key as being "hot", resulting in more stale value usage. + * + * Note that "check" keys won't collide with other regular keys. + * + * @see WANObjectCache::get() + * @see WANObjectCache::getWithSetCallback() + * @see WANObjectCache::resetCheckKey() + * + * @param string $key Cache key + * @param int $holdoff HOLDOFF_TTL or HOLDOFF_TTL_NONE constant + * @return bool True if the item was purged or not found, false on failure + */ + final public function touchCheckKey( $key, $holdoff = self::HOLDOFF_TTL ) { + // Publish the purge to all datacenters + $ok = $this->relayPurge( self::$TIME_KEY_PREFIX . $key, self::$CHECK_KEY_TTL, $holdoff ); + + $kClass = $this->determineKeyClassForStats( $key ); + $this->stats->increment( "wanobjectcache.$kClass.ck_touch." . ( $ok ? 'ok' : 'error' ) ); + + return $ok; + } + + /** + * Delete a "check" key from all datacenters, invalidating keys that use it + * + * This is similar to touchCheckKey() in that keys using it via get(), getMulti(), + * or getWithSetCallback() will be invalidated. The differences are: + * - a) The "check" key will be deleted from all caches and lazily + * re-initialized when accessed (rather than set everywhere) + * - b) Thus, dependent keys will be known to be stale, but not + * for how long (they are treated as "just" purged), which + * effects any lockTSE logic in getWithSetCallback() + * - c) Since "check" keys are initialized only on the server the key hashes + * to, any temporary ejection of that server will cause the value to be + * seen as purged as a new server will initialize the "check" key. + * + * The advantage here is that the "check" keys, which have high TTLs, will only + * be created when a get*() method actually uses that key. This is better when + * a large number of "check" keys are invalided in a short period of time. + * + * Note that "check" keys won't collide with other regular keys. + * + * @see WANObjectCache::get() + * @see WANObjectCache::getWithSetCallback() + * @see WANObjectCache::touchCheckKey() + * + * @param string $key Cache key + * @return bool True if the item was purged or not found, false on failure + */ + final public function resetCheckKey( $key ) { + // Publish the purge to all datacenters + $ok = $this->relayDelete( self::$TIME_KEY_PREFIX . $key ); + + $kClass = $this->determineKeyClassForStats( $key ); + $this->stats->increment( "wanobjectcache.$kClass.ck_reset." . ( $ok ? 'ok' : 'error' ) ); + + return $ok; + } + + /** + * Method to fetch/regenerate cache keys + * + * On cache miss, the key will be set to the callback result via set() + * (unless the callback returns false) and that result will be returned. + * The arguments supplied to the callback are: + * - $oldValue : current cache value or false if not present + * - &$ttl : a reference to the TTL which can be altered + * - &$setOpts : a reference to options for set() which can be altered + * - $oldAsOf : generation UNIX timestamp of $oldValue or null if not present (since 1.28) + * + * It is strongly recommended to set the 'lag' and 'since' fields to avoid race conditions + * that can cause stale values to get stuck at keys. Usually, callbacks ignore the current + * value, but it can be used to maintain "most recent X" values that come from time or + * sequence based source data, provided that the "as of" id/time is tracked. Note that + * preemptive regeneration and $checkKeys can result in a non-false current value. + * + * Usage of $checkKeys is similar to get() and getMulti(). However, rather than the caller + * having to inspect a "current time left" variable (e.g. $curTTL, $curTTLs), a cache + * regeneration will automatically be triggered using the callback. + * + * The $ttl argument and "hotTTR" option (in $opts) use time-dependant randomization + * to avoid stampedes. Keys that are slow to regenerate and either heavily used + * or subject to explicit (unpredictable) purges, may need additional mechanisms. + * The simplest way to avoid stampedes for such keys is to use 'lockTSE' (in $opts). + * If explicit purges are needed, also: + * - a) Pass $key into $checkKeys + * - b) Use touchCheckKey( $key ) instead of delete( $key ) + * + * Example usage (typical key): + * @code + * $catInfo = $cache->getWithSetCallback( + * // Key to store the cached value under + * $cache->makeKey( 'cat-attributes', $catId ), + * // Time-to-live (in seconds) + * $cache::TTL_MINUTE, + * // Function that derives the new key value + * function ( $oldValue, &$ttl, array &$setOpts ) { + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * return $dbr->selectRow( ... ); + * } + * ); + * @endcode + * + * Example usage (key that is expensive and hot): + * @code + * $catConfig = $cache->getWithSetCallback( + * // Key to store the cached value under + * $cache->makeKey( 'site-cat-config' ), + * // Time-to-live (in seconds) + * $cache::TTL_DAY, + * // Function that derives the new key value + * function ( $oldValue, &$ttl, array &$setOpts ) { + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * return CatConfig::newFromRow( $dbr->selectRow( ... ) ); + * }, + * [ + * // Calling touchCheckKey() on this key invalidates the cache + * 'checkKeys' => [ $cache->makeKey( 'site-cat-config' ) ], + * // Try to only let one datacenter thread manage cache updates at a time + * 'lockTSE' => 30, + * // Avoid querying cache servers multiple times in a web request + * 'pcTTL' => $cache::TTL_PROC_LONG + * ] + * ); + * @endcode + * + * Example usage (key with dynamic dependencies): + * @code + * $catState = $cache->getWithSetCallback( + * // Key to store the cached value under + * $cache->makeKey( 'cat-state', $cat->getId() ), + * // Time-to-live (seconds) + * $cache::TTL_HOUR, + * // Function that derives the new key value + * function ( $oldValue, &$ttl, array &$setOpts ) { + * // Determine new value from the DB + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * return CatState::newFromResults( $dbr->select( ... ) ); + * }, + * [ + * // The "check" keys that represent things the value depends on; + * // Calling touchCheckKey() on any of them invalidates the cache + * 'checkKeys' => [ + * $cache->makeKey( 'sustenance-bowls', $cat->getRoomId() ), + * $cache->makeKey( 'people-present', $cat->getHouseId() ), + * $cache->makeKey( 'cat-laws', $cat->getCityId() ), + * ] + * ] + * ); + * @endcode + * + * Example usage (key that is expensive with too many DB dependencies for "check keys"): + * @code + * $catToys = $cache->getWithSetCallback( + * // Key to store the cached value under + * $cache->makeKey( 'cat-toys', $catId ), + * // Time-to-live (seconds) + * $cache::TTL_HOUR, + * // Function that derives the new key value + * function ( $oldValue, &$ttl, array &$setOpts ) { + * // Determine new value from the DB + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * return CatToys::newFromResults( $dbr->select( ... ) ); + * }, + * [ + * // Get the highest timestamp of any of the cat's toys + * 'touchedCallback' => function ( $value ) use ( $catId ) { + * $dbr = wfGetDB( DB_REPLICA ); + * $ts = $dbr->selectField( 'cat_toys', 'MAX(ct_touched)', ... ); + * + * return wfTimestampOrNull( TS_UNIX, $ts ); + * }, + * // Avoid DB queries for repeated access + * 'pcTTL' => $cache::TTL_PROC_SHORT + * ] + * ); + * @endcode + * + * Example usage (hot key holding most recent 100 events): + * @code + * $lastCatActions = $cache->getWithSetCallback( + * // Key to store the cached value under + * $cache->makeKey( 'cat-last-actions', 100 ), + * // Time-to-live (in seconds) + * 10, + * // Function that derives the new key value + * function ( $oldValue, &$ttl, array &$setOpts ) { + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * // Start off with the last cached list + * $list = $oldValue ?: []; + * // Fetch the last 100 relevant rows in descending order; + * // only fetch rows newer than $list[0] to reduce scanning + * $rows = iterator_to_array( $dbr->select( ... ) ); + * // Merge them and get the new "last 100" rows + * return array_slice( array_merge( $new, $list ), 0, 100 ); + * }, + * [ + * // Try to only let one datacenter thread manage cache updates at a time + * 'lockTSE' => 30, + * // Use a magic value when no cache value is ready rather than stampeding + * 'busyValue' => 'computing' + * ] + * ); + * @endcode + * + * Example usage (key holding an LRU subkey:value map; this can avoid flooding cache with + * keys for an unlimited set of (constraint,situation) pairs, thereby avoiding elevated + * cache evictions and wasted memory): + * @code + * $catSituationTolerabilityCache = $this->cache->getWithSetCallback( + * // Group by constraint ID/hash, cat family ID/hash, or something else useful + * $this->cache->makeKey( 'cat-situation-tolerability-checks', $groupKey ), + * WANObjectCache::TTL_DAY, // rarely used groups should fade away + * // The $scenarioKey format is $constraintId: + * function ( $cacheMap ) use ( $scenarioKey, $constraintId, $situation ) { + * $lruCache = MapCacheLRU::newFromArray( $cacheMap ?: [], self::CACHE_SIZE ); + * $result = $lruCache->get( $scenarioKey ); // triggers LRU bump if present + * if ( $result === null || $this->isScenarioResultExpired( $result ) ) { + * $result = $this->checkScenarioTolerability( $constraintId, $situation ); + * $lruCache->set( $scenarioKey, $result, 3 / 8 ); + * } + * // Save the new LRU cache map and reset the map's TTL + * return $lruCache->toArray(); + * }, + * [ + * // Once map is > 1 sec old, consider refreshing + * 'ageNew' => 1, + * // Update within 5 seconds after "ageNew" given a 1hz cache check rate + * 'hotTTR' => 5, + * // Avoid querying cache servers multiple times in a request; this also means + * // that a request can only alter the value of any given constraint key once + * 'pcTTL' => WANObjectCache::TTL_PROC_LONG + * ] + * ); + * $tolerability = isset( $catSituationTolerabilityCache[$scenarioKey] ) + * ? $catSituationTolerabilityCache[$scenarioKey] + * : $this->checkScenarioTolerability( $constraintId, $situation ); + * @endcode + * + * @see WANObjectCache::get() + * @see WANObjectCache::set() + * + * @param string $key Cache key made from makeKey() or makeGlobalKey() + * @param int $ttl Seconds to live for key updates. Special values are: + * - WANObjectCache::TTL_INDEFINITE: Cache forever (subject to LRU-style evictions) + * - WANObjectCache::TTL_UNCACHEABLE: Do not cache (if the key exists, it is not deleted) + * @param callable $callback Value generation function + * @param array $opts Options map: + * - checkKeys: List of "check" keys. The key at $key will be seen as stale when either + * touchCheckKey() or resetCheckKey() is called on any of the keys in this list. This + * is useful if thousands or millions of keys depend on the same entity. The entity can + * simply have its "check" key updated whenever the entity is modified. + * Default: []. + * - graceTTL: If the key is invalidated (by "checkKeys"/"touchedCallback") less than this + * many seconds ago, consider reusing the stale value. The odds of a refresh becomes + * more likely over time, becoming certain once the grace period is reached. This can + * reduce traffic spikes when millions of keys are compared to the same "check" key and + * touchCheckKey() or resetCheckKey() is called on that "check" key. This option is not + * useful for avoiding traffic spikes in the case of the key simply expiring on account + * of its TTL (use "lowTTL" instead). + * Default: WANObjectCache::GRACE_TTL_NONE. + * - lockTSE: If the key is tombstoned or invalidated (by "checkKeys"/"touchedCallback") + * less than this many seconds ago, try to have a single thread handle cache regeneration + * at any given time. Other threads will use stale values if possible. If, on miss, + * the time since expiration is low, the assumption is that the key is hot and that a + * stampede is worth avoiding. Note that if the key falls out of cache then concurrent + * threads will all run the callback on cache miss until the value is saved in cache. + * The only stampede protection in that case is from duplicate cache sets when the + * callback takes longer than WANObjectCache::SET_DELAY_HIGH_MS milliseconds; consider + * using "busyValue" if such stampedes are a problem. Note that the higher "lockTSE" is + * set, the higher the worst-case staleness of returned values can be. Also note that + * this option does not by itself handle the case of the key simply expiring on account + * of its TTL, so make sure that "lowTTL" is not disabled when using this option. Avoid + * combining this option with delete() as it can always cause a stampede due to their + * being no stale value available until after a thread completes the callback. + * Use WANObjectCache::TSE_NONE to disable this logic. + * Default: WANObjectCache::TSE_NONE. + * - busyValue: Specify a placeholder value to use when no value exists and another thread + * is currently regenerating it. This assures that cache stampedes cannot happen if the + * value falls out of cache. This also mitigates stampedes when value regeneration + * becomes very slow (greater than $ttl/"lowTTL"). If this is a closure, then it will + * be invoked to get the placeholder when needed. + * Default: null. + * - pcTTL: Process cache the value in this PHP instance for this many seconds. This avoids + * network I/O when a key is read several times. This will not cache when the callback + * returns false, however. Note that any purges will not be seen while process cached; + * since the callback should use replica DBs and they may be lagged or have snapshot + * isolation anyway, this should not typically matter. + * Default: WANObjectCache::TTL_UNCACHEABLE. + * - pcGroup: Process cache group to use instead of the primary one. If set, this must be + * of the format ALPHANUMERIC_NAME:MAX_KEY_SIZE, e.g. "mydata:10". Use this for storing + * large values, small yet numerous values, or some values with a high cost of eviction. + * It is generally preferable to use a class constant when setting this value. + * This has no effect unless pcTTL is used. + * Default: WANObjectCache::PC_PRIMARY. + * - version: Integer version number. This lets callers make breaking changes to the format + * of cached values without causing problems for sites that use non-instantaneous code + * deployments. Old and new code will recognize incompatible versions and purges from + * both old and new code will been seen by each other. When this method encounters an + * incompatibly versioned value at the provided key, a "variant key" will be used for + * reading from and saving to cache. The variant key is specific to the key and version + * number provided to this method. If the variant key value is older than that of the + * provided key, or the provided key is non-existant, then the variant key will be seen + * as non-existant. Therefore, delete() calls invalidate the provided key's variant keys. + * The "checkKeys" and "touchedCallback" options still apply to variant keys as usual. + * Avoid storing class objects, as this reduces compatibility (due to serialization). + * Default: null. + * - minAsOf: Reject values if they were generated before this UNIX timestamp. + * This is useful if the source of a key is suspected of having possibly changed + * recently, and the caller wants any such changes to be reflected. + * Default: WANObjectCache::MIN_TIMESTAMP_NONE. + * - hotTTR: Expected time-till-refresh (TTR) in seconds for keys that average ~1 hit per + * second (e.g. 1Hz). Keys with a hit rate higher than 1Hz will refresh sooner than this + * TTR and vise versa. Such refreshes won't happen until keys are "ageNew" seconds old. + * This uses randomization to avoid triggering cache stampedes. The TTR is useful at + * reducing the impact of missed cache purges, since the effect of a heavily referenced + * key being stale is worse than that of a rarely referenced key. Unlike simply lowering + * $ttl, seldomly used keys are largely unaffected by this option, which makes it + * possible to have a high hit rate for the "long-tail" of less-used keys. + * Default: WANObjectCache::HOT_TTR. + * - lowTTL: Consider pre-emptive updates when the current TTL (seconds) of the key is less + * than this. It becomes more likely over time, becoming certain once the key is expired. + * This helps avoid cache stampedes that might be triggered due to the key expiring. + * Default: WANObjectCache::LOW_TTL. + * - ageNew: Consider popularity refreshes only once a key reaches this age in seconds. + * Default: WANObjectCache::AGE_NEW. + * - staleTTL: Seconds to keep the key around if it is stale. This means that on cache + * miss the callback may get $oldValue/$oldAsOf values for keys that have already been + * expired for this specified time. This is useful if adaptiveTTL() is used on the old + * value's as-of time when it is verified as still being correct. + * Default: WANObjectCache::STALE_TTL_NONE + * - touchedCallback: A callback that takes the current value and returns a UNIX timestamp + * indicating the last time a dynamic dependency changed. Null can be returned if there + * are no relevant dependency changes to check. This can be used to check against things + * like last-modified times of files or DB timestamp fields. This should generally not be + * used for small and easily queried values in a DB if the callback itself ends up doing + * a similarly expensive DB query to check a timestamp. Usages of this option makes the + * most sense for values that are moderately to highly expensive to regenerate and easy + * to query for dependency timestamps. The use of "pcTTL" reduces timestamp queries. + * Default: null. + * @return mixed Value found or written to the key + * @note Options added in 1.28: version, busyValue, hotTTR, ageNew, pcGroup, minAsOf + * @note Options added in 1.31: staleTTL, graceTTL + * @note Options added in 1.33: touchedCallback + * @note Callable type hints are not used to avoid class-autoloading + */ + final public function getWithSetCallback( $key, $ttl, $callback, array $opts = [] ) { + $version = $opts['version'] ?? null; + $pcTTL = $opts['pcTTL'] ?? self::TTL_UNCACHEABLE; + $pCache = ( $pcTTL >= 0 ) + ? $this->getProcessCache( $opts['pcGroup'] ?? self::PC_PRIMARY ) + : null; + + // Use the process cache if requested as long as no outer cache callback is running. + // Nested callback process cache use is not lag-safe with regard to HOLDOFF_TTL since + // process cached values are more lagged than persistent ones as they are not purged. + if ( $pCache && $this->callbackDepth == 0 ) { + $cached = $pCache->get( $this->getProcessCacheKey( $key, $version ), INF, false ); + if ( $cached !== false ) { + return $cached; + } + } + + $res = $this->fetchOrRegenerate( $key, $ttl, $callback, $opts ); + list( $value, $valueVersion, $curAsOf ) = $res; + if ( $valueVersion !== $version ) { + // Current value has a different version; use the variant key for this version. + // Regenerate the variant value if it is not newer than the main value at $key + // so that purges to the main key propagate to the variant value. + list( $value ) = $this->fetchOrRegenerate( + $this->makeGlobalKey( 'WANCache-key-variant', md5( $key ), $version ), + $ttl, + $callback, + [ 'version' => null, 'minAsOf' => $curAsOf ] + $opts + ); + } + + // Update the process cache if enabled + if ( $pCache && $value !== false ) { + $pCache->set( $this->getProcessCacheKey( $key, $version ), $value ); + } + + return $value; + } + + /** + * Do the actual I/O for getWithSetCallback() when needed + * + * @see WANObjectCache::getWithSetCallback() + * + * @param string $key + * @param int $ttl + * @param callable $callback + * @param array $opts Options map for getWithSetCallback() + * @return array Ordered list of the following: + * - Cached or regenerated value + * - Cached or regenerated value version number or null if not versioned + * - Timestamp of the current cached value at the key or null if there is no value + * @note Callable type hints are not used to avoid class-autoloading + */ + private function fetchOrRegenerate( $key, $ttl, $callback, array $opts ) { + $checkKeys = $opts['checkKeys'] ?? []; + $graceTTL = $opts['graceTTL'] ?? self::GRACE_TTL_NONE; + $minAsOf = $opts['minAsOf'] ?? self::MIN_TIMESTAMP_NONE; + $hotTTR = $opts['hotTTR'] ?? self::HOT_TTR; + $lowTTL = $opts['lowTTL'] ?? min( self::LOW_TTL, $ttl ); + $ageNew = $opts['ageNew'] ?? self::AGE_NEW; + $touchedCb = $opts['touchedCallback'] ?? null; + $initialTime = $this->getCurrentTime(); + + $kClass = $this->determineKeyClassForStats( $key ); + + // Get the current key value and its metadata + $curTTL = self::PASS_BY_REF; + $curInfo = self::PASS_BY_REF; /** @var array $curInfo */ + $curValue = $this->get( $key, $curTTL, $checkKeys, $curInfo ); + // Apply any $touchedCb invalidation timestamp to get the "last purge timestamp" + list( $curTTL, $LPT ) = $this->resolveCTL( $curValue, $curTTL, $curInfo, $touchedCb ); + // Use the cached value if it exists and is not due for synchronous regeneration + if ( + $this->isValid( $curValue, $curInfo['asOf'], $minAsOf ) && + $this->isAliveOrInGracePeriod( $curTTL, $graceTTL ) + ) { + $preemptiveRefresh = ( + $this->worthRefreshExpiring( $curTTL, $lowTTL ) || + $this->worthRefreshPopular( $curInfo['asOf'], $ageNew, $hotTTR, $initialTime ) + ); + if ( !$preemptiveRefresh ) { + $this->stats->increment( "wanobjectcache.$kClass.hit.good" ); + + return [ $curValue, $curInfo['version'], $curInfo['asOf'] ]; + } elseif ( $this->scheduleAsyncRefresh( $key, $ttl, $callback, $opts ) ) { + $this->stats->increment( "wanobjectcache.$kClass.hit.refresh" ); + + return [ $curValue, $curInfo['version'], $curInfo['asOf'] ]; + } + } + + // Determine if there is stale or volatile cached value that is still usable + $isKeyTombstoned = ( $curInfo['tombAsOf'] !== null ); + if ( $isKeyTombstoned ) { + // Key is write-holed; use the (volatile) interim key as an alternative + list( $possValue, $possInfo ) = $this->getInterimValue( $key, $minAsOf ); + // Update the "last purge time" since the $touchedCb timestamp depends on $value + $LPT = $this->resolveTouched( $possValue, $LPT, $touchedCb ); + } else { + $possValue = $curValue; + $possInfo = $curInfo; + } + + // Avoid overhead from callback runs, regeneration locks, and cache sets during + // hold-off periods for the key by reusing very recently generated cached values + if ( + $this->isValid( $possValue, $possInfo['asOf'], $minAsOf, $LPT ) && + $this->isVolatileValueAgeNegligible( $initialTime - $possInfo['asOf'] ) + ) { + $this->stats->increment( "wanobjectcache.$kClass.hit.volatile" ); + + return [ $possValue, $possInfo['version'], $curInfo['asOf'] ]; + } + + $lockTSE = $opts['lockTSE'] ?? self::TSE_NONE; + $busyValue = $opts['busyValue'] ?? null; + $staleTTL = $opts['staleTTL'] ?? self::STALE_TTL_NONE; + $version = $opts['version'] ?? null; + + // Determine whether one thread per datacenter should handle regeneration at a time + $useRegenerationLock = + // Note that since tombstones no-op set(), $lockTSE and $curTTL cannot be used to + // deduce the key hotness because |$curTTL| will always keep increasing until the + // tombstone expires or is overwritten by a new tombstone. Also, even if $lockTSE + // is not set, constant regeneration of a key for the tombstone lifetime might be + // very expensive. Assume tombstoned keys are possibly hot in order to reduce + // the risk of high regeneration load after the delete() method is called. + $isKeyTombstoned || + // Assume a key is hot if requested soon ($lockTSE seconds) after invalidation. + // This avoids stampedes when timestamps from $checkKeys/$touchedCb bump. + ( $curTTL !== null && $curTTL <= 0 && abs( $curTTL ) <= $lockTSE ) || + // Assume a key is hot if there is no value and a busy fallback is given. + // This avoids stampedes on eviction or preemptive regeneration taking too long. + ( $busyValue !== null && $possValue === false ); + + // If a regeneration lock is required, threads that do not get the lock will try to use + // the stale value, the interim value, or the $busyValue placeholder, in that order. If + // none of those are set then all threads will bypass the lock and regenerate the value. + $hasLock = $useRegenerationLock && $this->claimStampedeLock( $key ); + if ( $useRegenerationLock && !$hasLock ) { + if ( $this->isValid( $possValue, $possInfo['asOf'], $minAsOf ) ) { + $this->stats->increment( "wanobjectcache.$kClass.hit.stale" ); + + return [ $possValue, $possInfo['version'], $curInfo['asOf'] ]; + } elseif ( $busyValue !== null ) { + $miss = is_infinite( $minAsOf ) ? 'renew' : 'miss'; + $this->stats->increment( "wanobjectcache.$kClass.$miss.busy" ); + + return [ $this->resolveBusyValue( $busyValue ), $version, $curInfo['asOf'] ]; + } + } + + // Generate the new value given any prior value with a matching version + $setOpts = []; + $preCallbackTime = $this->getCurrentTime(); + ++$this->callbackDepth; + try { + $value = $callback( + ( $curInfo['version'] === $version ) ? $curValue : false, + $ttl, + $setOpts, + ( $curInfo['version'] === $version ) ? $curInfo['asOf'] : null + ); + } finally { + --$this->callbackDepth; + } + $postCallbackTime = $this->getCurrentTime(); + + // How long it took to fetch, validate, and generate the value + $elapsed = max( $postCallbackTime - $initialTime, 0.0 ); + + // Attempt to save the newly generated value if applicable + if ( + // Callback yielded a cacheable value + ( $value !== false && $ttl >= 0 ) && + // Current thread was not raced out of a regeneration lock or key is tombstoned + ( !$useRegenerationLock || $hasLock || $isKeyTombstoned ) && + // Key does not appear to be undergoing a set() stampede + $this->checkAndSetCooloff( $key, $kClass, $elapsed, $lockTSE, $hasLock ) + ) { + // How long it took to generate the value + $walltime = max( $postCallbackTime - $preCallbackTime, 0.0 ); + $this->stats->timing( "wanobjectcache.$kClass.regen_walltime", 1e3 * $walltime ); + // If the key is write-holed then use the (volatile) interim key as an alternative + if ( $isKeyTombstoned ) { + $this->setInterimValue( $key, $value, $lockTSE, $version, $walltime ); + } else { + $finalSetOpts = [ + 'since' => $setOpts['since'] ?? $preCallbackTime, + 'version' => $version, + 'staleTTL' => $staleTTL, + 'lockTSE' => $lockTSE, // informs lag vs performance trade-offs + 'creating' => ( $curValue === false ), // optimization + 'walltime' => $walltime + ] + $setOpts; + $this->set( $key, $value, $ttl, $finalSetOpts ); + } + } + + $this->yieldStampedeLock( $key, $hasLock ); + + $miss = is_infinite( $minAsOf ) ? 'renew' : 'miss'; + $this->stats->increment( "wanobjectcache.$kClass.$miss.compute" ); + + return [ $value, $version, $curInfo['asOf'] ]; + } + + /** + * @param string $key + * @return bool Success + */ + private function claimStampedeLock( $key ) { + // Note that locking is not bypassed due to I/O errors; this avoids stampedes + return $this->cache->add( self::$MUTEX_KEY_PREFIX . $key, 1, self::$LOCK_TTL ); + } + + /** + * @param string $key + * @param bool $hasLock + */ + private function yieldStampedeLock( $key, $hasLock ) { + if ( $hasLock ) { + // The backend might be a mcrouter proxy set to broadcast DELETE to *all* the local + // datacenter cache servers via OperationSelectorRoute (for increased consistency). + // Since that would be excessive for these locks, use TOUCH to expire the key. + $this->cache->changeTTL( self::$MUTEX_KEY_PREFIX . $key, $this->getCurrentTime() - 60 ); + } + } + + /** + * @param float $age Age of volatile/interim key in seconds + * @return bool Whether the age of a volatile value is negligible + */ + private function isVolatileValueAgeNegligible( $age ) { + return ( $age < mt_rand( self::$RECENT_SET_LOW_MS, self::$RECENT_SET_HIGH_MS ) / 1e3 ); + } + + /** + * @param string $key + * @param string $kClass + * @param float $elapsed Seconds spent regenerating the value + * @param float $lockTSE + * @param bool $hasLock + * @return bool Whether it is OK to proceed with a key set operation + */ + private function checkAndSetCooloff( $key, $kClass, $elapsed, $lockTSE, $hasLock ) { + $this->stats->timing( "wanobjectcache.$kClass.regen_set_delay", 1e3 * $elapsed ); + + // If $lockTSE is set, the lock was bypassed because there was no stale/interim value, + // and $elapsed indicates that regeration is slow, then there is a risk of set() + // stampedes with large blobs. With a typical scale-out infrastructure, CPU and query + // load from $callback invocations is distributed among appservers and replica DBs, + // but cache operations for a given key route to a single cache server (e.g. striped + // consistent hashing). + if ( $lockTSE < 0 || $hasLock ) { + return true; // either not a priori hot or thread has the lock + } elseif ( $elapsed <= self::$SET_DELAY_HIGH_MS * 1e3 ) { + return true; // not enough time for threads to pile up + } + + $this->cache->clearLastError(); + if ( + !$this->cache->add( self::$COOLOFF_KEY_PREFIX . $key, 1, self::$COOLOFF_TTL ) && + // Don't treat failures due to I/O errors as the key being in cooloff + $this->cache->getLastError() === BagOStuff::ERR_NONE + ) { + $this->stats->increment( "wanobjectcache.$kClass.cooloff_bounce" ); + + return false; + } + + return true; + } + + /** + * @param mixed $value + * @param float|null $curTTL + * @param array $curInfo + * @param callable|null $touchedCallback + * @return array (current time left or null, UNIX timestamp of last purge or null) + * @note Callable type hints are not used to avoid class-autoloading + */ + private function resolveCTL( $value, $curTTL, $curInfo, $touchedCallback ) { + if ( $touchedCallback === null || $value === false ) { + return [ $curTTL, max( $curInfo['tombAsOf'], $curInfo['lastCKPurge'] ) ]; + } + + $touched = $touchedCallback( $value ); + if ( $touched !== null && $touched >= $curInfo['asOf'] ) { + $curTTL = min( $curTTL, self::$TINY_NEGATIVE, $curInfo['asOf'] - $touched ); + } + + return [ $curTTL, max( $curInfo['tombAsOf'], $curInfo['lastCKPurge'], $touched ) ]; + } + + /** + * @param mixed $value + * @param float|null $lastPurge + * @param callable|null $touchedCallback + * @return float|null UNIX timestamp of last purge or null + * @note Callable type hints are not used to avoid class-autoloading + */ + private function resolveTouched( $value, $lastPurge, $touchedCallback ) { + return ( $touchedCallback === null || $value === false ) + ? $lastPurge // nothing to derive the "touched timestamp" from + : max( $touchedCallback( $value ), $lastPurge ); + } + + /** + * @param string $key + * @param float $minAsOf Minimum acceptable "as of" timestamp + * @return array (cached value or false, cache key metadata map) + */ + private function getInterimValue( $key, $minAsOf ) { + $now = $this->getCurrentTime(); + + if ( $this->useInterimHoldOffCaching ) { + $wrapped = $this->cache->get( self::$INTERIM_KEY_PREFIX . $key ); + + list( $value, $keyInfo ) = $this->unwrap( $wrapped, $now ); + if ( $this->isValid( $value, $keyInfo['asOf'], $minAsOf ) ) { + return [ $value, $keyInfo ]; + } + } + + return $this->unwrap( false, $now ); + } + + /** + * @param string $key + * @param mixed $value + * @param int $ttl + * @param int|null $version Value version number + * @param float $walltime How long it took to generate the value in seconds + */ + private function setInterimValue( $key, $value, $ttl, $version, $walltime ) { + $ttl = max( self::$INTERIM_KEY_TTL, (int)$ttl ); + + $wrapped = $this->wrap( $value, $ttl, $version, $this->getCurrentTime(), $walltime ); + $this->cache->merge( + self::$INTERIM_KEY_PREFIX . $key, + function () use ( $wrapped ) { + return $wrapped; + }, + $ttl, + 1 + ); + } + + /** + * @param mixed $busyValue + * @return mixed + */ + private function resolveBusyValue( $busyValue ) { + return ( $busyValue instanceof Closure ) ? $busyValue() : $busyValue; + } + + /** + * Method to fetch multiple cache keys at once with regeneration + * + * This works the same as getWithSetCallback() except: + * - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys() + * - b) The $callback argument expects a callback taking the following arguments: + * - $id: ID of an entity to query + * - $oldValue : the prior cache value or false if none was present + * - &$ttl : a reference to the new value TTL in seconds + * - &$setOpts : a reference to options for set() which can be altered + * - $oldAsOf : generation UNIX timestamp of $oldValue or null if not present + * Aside from the additional $id argument, the other arguments function the same + * way they do in getWithSetCallback(). + * - c) The return value is a map of (cache key => value) in the order of $keyedIds + * + * @see WANObjectCache::getWithSetCallback() + * @see WANObjectCache::getMultiWithUnionSetCallback() + * + * Example usage: + * @code + * $rows = $cache->getMultiWithSetCallback( + * // Map of cache keys to entity IDs + * $cache->makeMultiKeys( + * $this->fileVersionIds(), + * function ( $id ) use ( $cache ) { + * return $cache->makeKey( 'file-version', $id ); + * } + * ), + * // Time-to-live (in seconds) + * $cache::TTL_DAY, + * // Function that derives the new key value + * function ( $id, $oldValue, &$ttl, array &$setOpts ) { + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * // Load the row for this file + * $queryInfo = File::getQueryInfo(); + * $row = $dbr->selectRow( + * $queryInfo['tables'], + * $queryInfo['fields'], + * [ 'id' => $id ], + * __METHOD__, + * [], + * $queryInfo['joins'] + * ); + * + * return $row ? (array)$row : false; + * }, + * [ + * // Process cache for 30 seconds + * 'pcTTL' => 30, + * // Use a dedicated 500 item cache (initialized on-the-fly) + * 'pcGroup' => 'file-versions:500' + * ] + * ); + * $files = array_map( [ __CLASS__, 'newFromRow' ], $rows ); + * @endcode + * + * @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys() + * @param int $ttl Seconds to live for key updates + * @param callable $callback Callback the yields entity regeneration callbacks + * @param array $opts Options map + * @return mixed[] Map of (cache key => value) in the same order as $keyedIds + * @since 1.28 + */ + final public function getMultiWithSetCallback( + ArrayIterator $keyedIds, $ttl, callable $callback, array $opts = [] + ) { + // Load required keys into process cache in one go + $this->warmupCache = $this->getRawKeysForWarmup( + $this->getNonProcessCachedMultiKeys( $keyedIds, $opts ), + $opts['checkKeys'] ?? [] + ); + $this->warmupKeyMisses = 0; + + // Wrap $callback to match the getWithSetCallback() format while passing $id to $callback + $id = null; // current entity ID + $func = function ( $oldValue, &$ttl, &$setOpts, $oldAsOf ) use ( $callback, &$id ) { + return $callback( $id, $oldValue, $ttl, $setOpts, $oldAsOf ); + }; + + $values = []; + foreach ( $keyedIds as $key => $id ) { // preserve order + $values[$key] = $this->getWithSetCallback( $key, $ttl, $func, $opts ); + } + + $this->warmupCache = []; + + return $values; + } + + /** + * Method to fetch/regenerate multiple cache keys at once + * + * This works the same as getWithSetCallback() except: + * - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys() + * - b) The $callback argument expects a callback returning a map of (ID => new value) + * for all entity IDs in $ids and it takes the following arguments: + * - $ids: a list of entity IDs that require cache regeneration + * - &$ttls: a reference to the (entity ID => new TTL) map + * - &$setOpts: a reference to options for set() which can be altered + * - c) The return value is a map of (cache key => value) in the order of $keyedIds + * - d) The "lockTSE" and "busyValue" options are ignored + * + * @see WANObjectCache::getWithSetCallback() + * @see WANObjectCache::getMultiWithSetCallback() + * + * Example usage: + * @code + * $rows = $cache->getMultiWithUnionSetCallback( + * // Map of cache keys to entity IDs + * $cache->makeMultiKeys( + * $this->fileVersionIds(), + * function ( $id ) use ( $cache ) { + * return $cache->makeKey( 'file-version', $id ); + * } + * ), + * // Time-to-live (in seconds) + * $cache::TTL_DAY, + * // Function that derives the new key value + * function ( array $ids, array &$ttls, array &$setOpts ) { + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * // Load the rows for these files + * $rows = []; + * $queryInfo = File::getQueryInfo(); + * $res = $dbr->select( + * $queryInfo['tables'], + * $queryInfo['fields'], + * [ 'id' => $ids ], + * __METHOD__, + * [], + * $queryInfo['joins'] + * ); + * foreach ( $res as $row ) { + * $rows[$row->id] = $row; + * $mtime = wfTimestamp( TS_UNIX, $row->timestamp ); + * $ttls[$row->id] = $this->adaptiveTTL( $mtime, $ttls[$row->id] ); + * } + * + * return $rows; + * }, + * ] + * ); + * $files = array_map( [ __CLASS__, 'newFromRow' ], $rows ); + * @endcode + * + * @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys() + * @param int $ttl Seconds to live for key updates + * @param callable $callback Callback the yields entity regeneration callbacks + * @param array $opts Options map + * @return mixed[] Map of (cache key => value) in the same order as $keyedIds + * @since 1.30 + */ + final public function getMultiWithUnionSetCallback( + ArrayIterator $keyedIds, $ttl, callable $callback, array $opts = [] + ) { + $checkKeys = $opts['checkKeys'] ?? []; + unset( $opts['lockTSE'] ); // incompatible + unset( $opts['busyValue'] ); // incompatible + + // Load required keys into process cache in one go + $keysByIdGet = $this->getNonProcessCachedMultiKeys( $keyedIds, $opts ); + $this->warmupCache = $this->getRawKeysForWarmup( $keysByIdGet, $checkKeys ); + $this->warmupKeyMisses = 0; + + // IDs of entities known to be in need of regeneration + $idsRegen = []; + + // Find out which keys are missing/deleted/stale + $curTTLs = []; + $asOfs = []; + $curByKey = $this->getMulti( $keysByIdGet, $curTTLs, $checkKeys, $asOfs ); + foreach ( $keysByIdGet as $id => $key ) { + if ( !array_key_exists( $key, $curByKey ) || $curTTLs[$key] < 0 ) { + $idsRegen[] = $id; + } + } + + // Run the callback to populate the regeneration value map for all required IDs + $newSetOpts = []; + $newTTLsById = array_fill_keys( $idsRegen, $ttl ); + $newValsById = $idsRegen ? $callback( $idsRegen, $newTTLsById, $newSetOpts ) : []; + + // Wrap $callback to match the getWithSetCallback() format while passing $id to $callback + $id = null; // current entity ID + $func = function ( $oldValue, &$ttl, &$setOpts, $oldAsOf ) + use ( $callback, &$id, $newValsById, $newTTLsById, $newSetOpts ) + { + if ( array_key_exists( $id, $newValsById ) ) { + // Value was already regerated as expected, so use the value in $newValsById + $newValue = $newValsById[$id]; + $ttl = $newTTLsById[$id]; + $setOpts = $newSetOpts; + } else { + // Pre-emptive/popularity refresh and version mismatch cases are not detected + // above and thus $newValsById has no entry. Run $callback on this single entity. + $ttls = [ $id => $ttl ]; + $newValue = $callback( [ $id ], $ttls, $setOpts )[$id]; + $ttl = $ttls[$id]; + } + + return $newValue; + }; + + // Run the cache-aside logic using warmupCache instead of persistent cache queries + $values = []; + foreach ( $keyedIds as $key => $id ) { // preserve order + $values[$key] = $this->getWithSetCallback( $key, $ttl, $func, $opts ); + } + + $this->warmupCache = []; + + return $values; + } + + /** + * Set a key to soon expire in the local cluster if it pre-dates $purgeTimestamp + * + * This sets stale keys' time-to-live at HOLDOFF_TTL seconds, which both avoids + * broadcasting in mcrouter setups and also avoids races with new tombstones. + * + * @param string $key Cache key + * @param int $purgeTimestamp UNIX timestamp of purge + * @param bool &$isStale Whether the key is stale + * @return bool Success + * @since 1.28 + */ + final public function reap( $key, $purgeTimestamp, &$isStale = false ) { + $minAsOf = $purgeTimestamp + self::HOLDOFF_TTL; + $wrapped = $this->cache->get( self::$VALUE_KEY_PREFIX . $key ); + if ( is_array( $wrapped ) && $wrapped[self::$FLD_TIME] < $minAsOf ) { + $isStale = true; + $this->logger->warning( "Reaping stale value key '$key'." ); + $ttlReap = self::HOLDOFF_TTL; // avoids races with tombstone creation + $ok = $this->cache->changeTTL( self::$VALUE_KEY_PREFIX . $key, $ttlReap ); + if ( !$ok ) { + $this->logger->error( "Could not complete reap of key '$key'." ); + } + + return $ok; + } + + $isStale = false; + + return true; + } + + /** + * Set a "check" key to soon expire in the local cluster if it pre-dates $purgeTimestamp + * + * @param string $key Cache key + * @param int $purgeTimestamp UNIX timestamp of purge + * @param bool &$isStale Whether the key is stale + * @return bool Success + * @since 1.28 + */ + final public function reapCheckKey( $key, $purgeTimestamp, &$isStale = false ) { + $purge = $this->parsePurgeValue( $this->cache->get( self::$TIME_KEY_PREFIX . $key ) ); + if ( $purge && $purge[self::$PURGE_TIME] < $purgeTimestamp ) { + $isStale = true; + $this->logger->warning( "Reaping stale check key '$key'." ); + $ok = $this->cache->changeTTL( self::$TIME_KEY_PREFIX . $key, self::TTL_SECOND ); + if ( !$ok ) { + $this->logger->error( "Could not complete reap of check key '$key'." ); + } + + return $ok; + } + + $isStale = false; + + return false; + } + + /** + * @see BagOStuff::makeKey() + * @param string $class Key class + * @param string ...$components Key components (starting with a key collection name) + * @return string Colon-delimited list of $keyspace followed by escaped components + * @since 1.27 + */ + public function makeKey( $class, ...$components ) { + return $this->cache->makeKey( ...func_get_args() ); + } + + /** + * @see BagOStuff::makeGlobalKey() + * @param string $class Key class + * @param string ...$components Key components (starting with a key collection name) + * @return string Colon-delimited list of $keyspace followed by escaped components + * @since 1.27 + */ + public function makeGlobalKey( $class, ...$components ) { + return $this->cache->makeGlobalKey( ...func_get_args() ); + } + + /** + * Hash a possibly long string into a suitable component for makeKey()/makeGlobalKey() + * + * @param string $component A raw component used in building a cache key + * @return string 64 character HMAC using a stable secret for public collision resistance + * @since 1.34 + */ + public function hash256( $component ) { + return hash_hmac( 'sha256', $component, $this->secret ); + } + + /** + * Get an iterator of (cache key => entity ID) for a list of entity IDs + * + * The callback takes an ID string and returns a key via makeKey()/makeGlobalKey(). + * There should be no network nor filesystem I/O used in the callback. The entity + * ID/key mapping must be 1:1 or an exception will be thrown. If hashing is needed, + * then use the hash256() method. + * + * Example usage for the default keyspace: + * @code + * $keyedIds = $cache->makeMultiKeys( + * $modules, + * function ( $module ) use ( $cache ) { + * return $cache->makeKey( 'module-info', $module ); + * } + * ); + * @endcode + * + * Example usage for mixed default and global keyspace: + * @code + * $keyedIds = $cache->makeMultiKeys( + * $filters, + * function ( $filter ) use ( $cache ) { + * return ( strpos( $filter, 'central:' ) === 0 ) + * ? $cache->makeGlobalKey( 'regex-filter', $filter ) + * : $cache->makeKey( 'regex-filter', $filter ) + * } + * ); + * @endcode + * + * Example usage with hashing: + * @code + * $keyedIds = $cache->makeMultiKeys( + * $urls, + * function ( $url ) use ( $cache ) { + * return $cache->makeKey( 'url-info', $cache->hash256( $url ) ); + * } + * ); + * @endcode + * + * @see WANObjectCache::makeKey() + * @see WANObjectCache::makeGlobalKey() + * @see WANObjectCache::hash256() + * + * @param string[]|int[] $ids List of entity IDs + * @param callable $keyCallback Function returning makeKey()/makeGlobalKey() on the input ID + * @return ArrayIterator Iterator of (cache key => ID); order of $ids is preserved + * @throws UnexpectedValueException + * @since 1.28 + */ + final public function makeMultiKeys( array $ids, $keyCallback ) { + $idByKey = []; + foreach ( $ids as $id ) { + // Discourage triggering of automatic makeKey() hashing in some backends + if ( strlen( $id ) > 64 ) { + $this->logger->warning( __METHOD__ . ": long ID '$id'; use hash256()" ); + } + $key = $keyCallback( $id, $this ); + // Edge case: ignore key collisions due to duplicate $ids like "42" and 42 + if ( !isset( $idByKey[$key] ) ) { + $idByKey[$key] = $id; + } elseif ( (string)$id !== (string)$idByKey[$key] ) { + throw new UnexpectedValueException( + "Cache key collision; IDs ('$id','{$idByKey[$key]}') map to '$key'" + ); + } + } + + return new ArrayIterator( $idByKey ); + } + + /** + * Get an (ID => value) map from (i) a non-unique list of entity IDs, and (ii) the list + * of corresponding entity values by first appearance of each ID in the entity ID list + * + * For use with getMultiWithSetCallback() and getMultiWithUnionSetCallback(). + * + * *Only* use this method if the entity ID/key mapping is trivially 1:1 without exception. + * Key generation method must utitilize the *full* entity ID in the key (not a hash of it). + * + * Example usage: + * @code + * $poems = $cache->getMultiWithSetCallback( + * $cache->makeMultiKeys( + * $uuids, + * function ( $uuid ) use ( $cache ) { + * return $cache->makeKey( 'poem', $uuid ); + * } + * ), + * $cache::TTL_DAY, + * function ( $uuid ) use ( $url ) { + * return $this->http->run( [ 'method' => 'GET', 'url' => "$url/$uuid" ] ); + * } + * ); + * $poemsByUUID = $cache->multiRemap( $uuids, $poems ); + * @endcode + * + * @see WANObjectCache::makeMultiKeys() + * @see WANObjectCache::getMultiWithSetCallback() + * @see WANObjectCache::getMultiWithUnionSetCallback() + * + * @param string[]|int[] $ids Entity ID list makeMultiKeys() + * @param mixed[] $res Result of getMultiWithSetCallback()/getMultiWithUnionSetCallback() + * @return mixed[] Map of (ID => value); order of $ids is preserved + * @since 1.34 + */ + final public function multiRemap( array $ids, array $res ) { + if ( count( $ids ) !== count( $res ) ) { + // If makeMultiKeys() is called on a list of non-unique IDs, then the resulting + // ArrayIterator will have less entries due to "first appearance" de-duplication + $ids = array_keys( array_flip( $ids ) ); + if ( count( $ids ) !== count( $res ) ) { + throw new UnexpectedValueException( "Multi-key result does not match ID list" ); + } + } + + return array_combine( $ids, $res ); + } + + /** + * Get the "last error" registered; clearLastError() should be called manually + * @return int ERR_* class constant for the "last error" registry + */ + final public function getLastError() { + $code = $this->cache->getLastError(); + switch ( $code ) { + case BagOStuff::ERR_NONE: + return self::ERR_NONE; + case BagOStuff::ERR_NO_RESPONSE: + return self::ERR_NO_RESPONSE; + case BagOStuff::ERR_UNREACHABLE: + return self::ERR_UNREACHABLE; + default: + return self::ERR_UNEXPECTED; + } + } + + /** + * Clear the "last error" registry + */ + final public function clearLastError() { + $this->cache->clearLastError(); + } + + /** + * Clear the in-process caches; useful for testing + * + * @since 1.27 + */ + public function clearProcessCache() { + $this->processCaches = []; + } + + /** + * Enable or disable the use of brief caching for tombstoned keys + * + * When a key is purged via delete(), there normally is a period where caching + * is hold-off limited to an extremely short time. This method will disable that + * caching, forcing the callback to run for any of: + * - WANObjectCache::getWithSetCallback() + * - WANObjectCache::getMultiWithSetCallback() + * - WANObjectCache::getMultiWithUnionSetCallback() + * + * This is useful when both: + * - a) the database used by the callback is known to be up-to-date enough + * for some particular purpose (e.g. replica DB has applied transaction X) + * - b) the caller needs to exploit that fact, and therefore needs to avoid the + * use of inherently volatile and possibly stale interim keys + * + * @see WANObjectCache::delete() + * @param bool $enabled Whether to enable interim caching + * @since 1.31 + */ + final public function useInterimHoldOffCaching( $enabled ) { + $this->useInterimHoldOffCaching = $enabled; + } + + /** + * @param int $flag ATTR_* class constant + * @return int QOS_* class constant + * @since 1.28 + */ + public function getQoS( $flag ) { + return $this->cache->getQoS( $flag ); + } + + /** + * Get a TTL that is higher for objects that have not changed recently + * + * This is useful for keys that get explicit purges and DB or purge relay + * lag is a potential concern (especially how it interacts with CDN cache) + * + * Example usage: + * @code + * // Last-modified time of page + * $mtime = wfTimestamp( TS_UNIX, $page->getTimestamp() ); + * // Get adjusted TTL. If $mtime is 3600 seconds ago and $minTTL/$factor left at + * // defaults, then $ttl is 3600 * .2 = 720. If $minTTL was greater than 720, then + * // $ttl would be $minTTL. If $maxTTL was smaller than 720, $ttl would be $maxTTL. + * $ttl = $cache->adaptiveTTL( $mtime, $cache::TTL_DAY ); + * @endcode + * + * Another use case is when there are no applicable "last modified" fields in the DB, + * and there are too many dependencies for explicit purges to be viable, and the rate of + * change to relevant content is unstable, and it is highly valued to have the cached value + * be as up-to-date as possible. + * + * Example usage: + * @code + * $query = ""; + * $idListFromComplexQuery = $cache->getWithSetCallback( + * $cache->makeKey( 'complex-graph-query', $hashOfQuery ), + * GraphQueryClass::STARTING_TTL, + * function ( $oldValue, &$ttl, array &$setOpts, $oldAsOf ) use ( $query, $cache ) { + * $gdb = $this->getReplicaGraphDbConnection(); + * // Account for any snapshot/replica DB lag + * $setOpts += GraphDatabase::getCacheSetOptions( $gdb ); + * + * $newList = iterator_to_array( $gdb->query( $query ) ); + * sort( $newList, SORT_NUMERIC ); // normalize + * + * $minTTL = GraphQueryClass::MIN_TTL; + * $maxTTL = GraphQueryClass::MAX_TTL; + * if ( $oldValue !== false ) { + * // Note that $oldAsOf is the last time this callback ran + * $ttl = ( $newList === $oldValue ) + * // No change: cache for 150% of the age of $oldValue + * ? $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, 1.5 ) + * // Changed: cache for 50% of the age of $oldValue + * : $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, .5 ); + * } + * + * return $newList; + * }, + * [ + * // Keep stale values around for doing comparisons for TTL calculations. + * // High values improve long-tail keys hit-rates, though might waste space. + * 'staleTTL' => GraphQueryClass::GRACE_TTL + * ] + * ); + * @endcode + * + * @param int|float $mtime UNIX timestamp + * @param int $maxTTL Maximum TTL (seconds) + * @param int $minTTL Minimum TTL (seconds); Default: 30 + * @param float $factor Value in the range (0,1); Default: .2 + * @return int Adaptive TTL + * @since 1.28 + */ + public function adaptiveTTL( $mtime, $maxTTL, $minTTL = 30, $factor = 0.2 ) { + if ( is_float( $mtime ) || ctype_digit( $mtime ) ) { + $mtime = (int)$mtime; // handle fractional seconds and string integers + } + + if ( !is_int( $mtime ) || $mtime <= 0 ) { + return $minTTL; // no last-modified time provided + } + + $age = $this->getCurrentTime() - $mtime; + + return (int)min( $maxTTL, max( $minTTL, $factor * $age ) ); + } + + /** + * @return int Number of warmup key cache misses last round + * @since 1.30 + */ + final public function getWarmupKeyMisses() { + return $this->warmupKeyMisses; + } + + /** + * Do the actual async bus purge of a key + * + * This must set the key to "PURGED::" + * + * @param string $key Cache key + * @param int $ttl Seconds to keep the tombstone around + * @param int $holdoff HOLDOFF_* constant controlling how long to ignore sets for this key + * @return bool Success + */ + protected function relayPurge( $key, $ttl, $holdoff ) { + if ( $this->mcrouterAware ) { + // See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup + // Wildcards select all matching routes, e.g. the WAN cluster on all DCs + $ok = $this->cache->set( + "/*/{$this->cluster}/{$key}", + $this->makePurgeValue( $this->getCurrentTime(), self::HOLDOFF_TTL_NONE ), + $ttl + ); + } else { + // This handles the mcrouter and the single-DC case + $ok = $this->cache->set( + $key, + $this->makePurgeValue( $this->getCurrentTime(), self::HOLDOFF_TTL_NONE ), + $ttl + ); + } + + return $ok; + } + + /** + * Do the actual async bus delete of a key + * + * @param string $key Cache key + * @return bool Success + */ + protected function relayDelete( $key ) { + if ( $this->mcrouterAware ) { + // See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup + // Wildcards select all matching routes, e.g. the WAN cluster on all DCs + $ok = $this->cache->delete( "/*/{$this->cluster}/{$key}" ); + } else { + // Some other proxy handles broadcasting or there is only one datacenter + $ok = $this->cache->delete( $key ); + } + + return $ok; + } + + /** + * @param string $key + * @param int $ttl Seconds to live + * @param callable $callback + * @param array $opts + * @return bool Success + * @note Callable type hints are not used to avoid class-autoloading + */ + private function scheduleAsyncRefresh( $key, $ttl, $callback, $opts ) { + if ( !$this->asyncHandler ) { + return false; + } + // Update the cache value later, such during post-send of an HTTP request + $func = $this->asyncHandler; + $func( function () use ( $key, $ttl, $callback, $opts ) { + $opts['minAsOf'] = INF; // force a refresh + $this->fetchOrRegenerate( $key, $ttl, $callback, $opts ); + } ); + + return true; + } + + /** + * Check if a key is fresh or in the grace window and thus due for randomized reuse + * + * If $curTTL > 0 (e.g. not expired) this returns true. Otherwise, the chance of returning + * true decrease steadily from 100% to 0% as the |$curTTL| moves from 0 to $graceTTL seconds. + * This handles widely varying levels of cache access traffic. + * + * If $curTTL <= -$graceTTL (e.g. already expired), then this returns false. + * + * @param float $curTTL Approximate TTL left on the key if present + * @param int $graceTTL Consider using stale values if $curTTL is greater than this + * @return bool + */ + private function isAliveOrInGracePeriod( $curTTL, $graceTTL ) { + if ( $curTTL > 0 ) { + return true; + } elseif ( $graceTTL <= 0 ) { + return false; + } + + $ageStale = abs( $curTTL ); // seconds of staleness + $curGTTL = ( $graceTTL - $ageStale ); // current grace-time-to-live + if ( $curGTTL <= 0 ) { + return false; // already out of grace period + } + + // Chance of using a stale value is the complement of the chance of refreshing it + return !$this->worthRefreshExpiring( $curGTTL, $graceTTL ); + } + + /** + * Check if a key is nearing expiration and thus due for randomized regeneration + * + * This returns false if $curTTL >= $lowTTL. Otherwise, the chance of returning true + * increases steadily from 0% to 100% as the $curTTL moves from $lowTTL to 0 seconds. + * This handles widely varying levels of cache access traffic. + * + * If $curTTL <= 0 (e.g. already expired), then this returns false. + * + * @param float $curTTL Approximate TTL left on the key if present + * @param float $lowTTL Consider a refresh when $curTTL is less than this + * @return bool + */ + protected function worthRefreshExpiring( $curTTL, $lowTTL ) { + if ( $lowTTL <= 0 ) { + return false; + } elseif ( $curTTL >= $lowTTL ) { + return false; + } elseif ( $curTTL <= 0 ) { + return false; + } + + $chance = ( 1 - $curTTL / $lowTTL ); + + return mt_rand( 1, 1e9 ) <= 1e9 * $chance; + } + + /** + * Check if a key is due for randomized regeneration due to its popularity + * + * This is used so that popular keys can preemptively refresh themselves for higher + * consistency (especially in the case of purge loss/delay). Unpopular keys can remain + * in cache with their high nominal TTL. This means popular keys keep good consistency, + * whether the data changes frequently or not, and long-tail keys get to stay in cache + * and get hits too. Similar to worthRefreshExpiring(), randomization is used. + * + * @param float $asOf UNIX timestamp of the value + * @param int $ageNew Age of key when this might recommend refreshing (seconds) + * @param int $timeTillRefresh Age of key when it should be refreshed if popular (seconds) + * @param float $now The current UNIX timestamp + * @return bool + */ + protected function worthRefreshPopular( $asOf, $ageNew, $timeTillRefresh, $now ) { + if ( $ageNew < 0 || $timeTillRefresh <= 0 ) { + return false; + } + + $age = $now - $asOf; + $timeOld = $age - $ageNew; + if ( $timeOld <= 0 ) { + return false; + } + + $popularHitsPerSec = 1; + // Lifecycle is: new, ramp-up refresh chance, full refresh chance. + // Note that the "expected # of refreshes" for the ramp-up time range is half + // of what it would be if P(refresh) was at its full value during that time range. + $refreshWindowSec = max( $timeTillRefresh - $ageNew - self::$RAMPUP_TTL / 2, 1 ); + // P(refresh) * (# hits in $refreshWindowSec) = (expected # of refreshes) + // P(refresh) * ($refreshWindowSec * $popularHitsPerSec) = 1 (by definition) + // P(refresh) = 1/($refreshWindowSec * $popularHitsPerSec) + $chance = 1 / ( $popularHitsPerSec * $refreshWindowSec ); + + // Ramp up $chance from 0 to its nominal value over RAMPUP_TTL seconds to avoid stampedes + $chance *= ( $timeOld <= self::$RAMPUP_TTL ) ? $timeOld / self::$RAMPUP_TTL : 1; + + return mt_rand( 1, 1e9 ) <= 1e9 * $chance; + } + + /** + * Check if $value is not false, versioned (if needed), and not older than $minTime (if set) + * + * @param array|bool $value + * @param float $asOf The time $value was generated + * @param float $minAsOf Minimum acceptable "as of" timestamp + * @param float|null $purgeTime The last time the value was invalidated + * @return bool + */ + protected function isValid( $value, $asOf, $minAsOf, $purgeTime = null ) { + // Avoid reading any key not generated after the latest delete() or touch + $safeMinAsOf = max( $minAsOf, $purgeTime + self::$TINY_POSTIVE ); + + if ( $value === false ) { + return false; + } elseif ( $safeMinAsOf > 0 && $asOf < $minAsOf ) { + return false; + } + + return true; + } + + /** + * @param mixed $value + * @param int $ttl Seconds to live or zero for "indefinite" + * @param int|null $version Value version number or null if not versioned + * @param float $now Unix Current timestamp just before calling set() + * @param float $walltime How long it took to generate the value in seconds + * @return array + */ + private function wrap( $value, $ttl, $version, $now, $walltime ) { + // Returns keys in ascending integer order for PHP7 array packing: + // https://nikic.github.io/2014/12/22/PHPs-new-hashtable-implementation.html + $wrapped = [ + self::$FLD_FORMAT_VERSION => self::$VERSION, + self::$FLD_VALUE => $value, + self::$FLD_TTL => $ttl, + self::$FLD_TIME => $now + ]; + if ( $version !== null ) { + $wrapped[self::$FLD_VALUE_VERSION] = $version; + } + if ( $walltime >= self::$GENERATION_SLOW_SEC ) { + $wrapped[self::$FLD_GENERATION_TIME] = $walltime; + } + + return $wrapped; + } + + /** + * @param array|string|bool $wrapped The entry at a cache key + * @param float $now Unix Current timestamp (preferrably pre-query) + * @return array (value or false if absent/tombstoned/malformed, value metadata map). + * The cache key metadata includes the following metadata: + * - asOf: UNIX timestamp of the value or null if there is no value + * - curTTL: remaining time-to-live (negative if tombstoned) or null if there is no value + * - version: value version number or null if the if there is no value + * - tombAsOf: UNIX timestamp of the tombstone or null if there is no tombstone + */ + private function unwrap( $wrapped, $now ) { + $value = false; + $info = [ 'asOf' => null, 'curTTL' => null, 'version' => null, 'tombAsOf' => null ]; + + if ( is_array( $wrapped ) ) { + // Entry expected to be a cached value; validate it + if ( + ( $wrapped[self::$FLD_FORMAT_VERSION] ?? null ) === self::$VERSION && + $wrapped[self::$FLD_TIME] >= $this->epoch + ) { + if ( $wrapped[self::$FLD_TTL] > 0 ) { + // Get the approximate time left on the key + $age = $now - $wrapped[self::$FLD_TIME]; + $curTTL = max( $wrapped[self::$FLD_TTL] - $age, 0.0 ); + } else { + // Key had no TTL, so the time left is unbounded + $curTTL = INF; + } + $value = $wrapped[self::$FLD_VALUE]; + $info['version'] = $wrapped[self::$FLD_VALUE_VERSION] ?? null; + $info['asOf'] = $wrapped[self::$FLD_TIME]; + $info['curTTL'] = $curTTL; + } + } else { + // Entry expected to be a tombstone; parse it + $purge = $this->parsePurgeValue( $wrapped ); + if ( $purge !== false ) { + // Tombstoned keys should always have a negative current $ttl + $info['curTTL'] = min( $purge[self::$PURGE_TIME] - $now, self::$TINY_NEGATIVE ); + $info['tombAsOf'] = $purge[self::$PURGE_TIME]; + } + } + + return [ $value, $info ]; + } + + /** + * @param string[] $keys + * @param string $prefix + * @return string[] Prefix keys; the order of $keys is preserved + */ + protected static function prefixCacheKeys( array $keys, $prefix ) { + $res = []; + foreach ( $keys as $key ) { + $res[] = $prefix . $key; + } + + return $res; + } + + /** + * @param string $key String of the format :[:]... + * @return string A collection name to describe this class of key + */ + private function determineKeyClassForStats( $key ) { + $parts = explode( ':', $key, 3 ); + + return $parts[1] ?? $parts[0]; // sanity + } + + /** + * @param string|array|bool $value Possible string of the form "PURGED::" + * @return array|bool Array containing a UNIX timestamp (float) and holdoff period (integer), + * or false if value isn't a valid purge value + */ + private function parsePurgeValue( $value ) { + if ( !is_string( $value ) ) { + return false; + } + + $segments = explode( ':', $value, 3 ); + if ( + !isset( $segments[0] ) || + !isset( $segments[1] ) || + "{$segments[0]}:" !== self::$PURGE_VAL_PREFIX + ) { + return false; + } + + if ( !isset( $segments[2] ) ) { + // Back-compat with old purge values without holdoff + $segments[2] = self::HOLDOFF_TTL; + } + + if ( $segments[1] < $this->epoch ) { + // Values this old are ignored + return false; + } + + return [ + self::$PURGE_TIME => (float)$segments[1], + self::$PURGE_HOLDOFF => (int)$segments[2], + ]; + } + + /** + * @param float $timestamp + * @param int $holdoff In seconds + * @return string Wrapped purge value + */ + private function makePurgeValue( $timestamp, $holdoff ) { + return self::$PURGE_VAL_PREFIX . (float)$timestamp . ':' . (int)$holdoff; + } + + /** + * @param string $group + * @return MapCacheLRU + */ + private function getProcessCache( $group ) { + if ( !isset( $this->processCaches[$group] ) ) { + list( , $size ) = explode( ':', $group ); + $this->processCaches[$group] = new MapCacheLRU( (int)$size ); + } + + return $this->processCaches[$group]; + } + + /** + * @param string $key + * @param int $version + * @return string + */ + private function getProcessCacheKey( $key, $version ) { + return $key . ' ' . (int)$version; + } + + /** + * @param ArrayIterator $keys + * @param array $opts + * @return string[] Map of (ID => cache key) + */ + private function getNonProcessCachedMultiKeys( ArrayIterator $keys, array $opts ) { + $pcTTL = $opts['pcTTL'] ?? self::TTL_UNCACHEABLE; + + $keysMissing = []; + if ( $pcTTL > 0 && $this->callbackDepth == 0 ) { + $version = $opts['version'] ?? null; + $pCache = $this->getProcessCache( $opts['pcGroup'] ?? self::PC_PRIMARY ); + foreach ( $keys as $key => $id ) { + if ( !$pCache->has( $this->getProcessCacheKey( $key, $version ), $pcTTL ) ) { + $keysMissing[$id] = $key; + } + } + } + + return $keysMissing; + } + + /** + * @param string[] $keys + * @param string[]|string[][] $checkKeys + * @return string[] List of cache keys + */ + private function getRawKeysForWarmup( array $keys, array $checkKeys ) { + if ( !$keys ) { + return []; + } + + $keysWarmUp = []; + // Get all the value keys to fetch... + foreach ( $keys as $key ) { + $keysWarmUp[] = self::$VALUE_KEY_PREFIX . $key; + } + // Get all the check keys to fetch... + foreach ( $checkKeys as $i => $checkKeyOrKeys ) { + if ( is_int( $i ) ) { + // Single check key that applies to all value keys + $keysWarmUp[] = self::$TIME_KEY_PREFIX . $checkKeyOrKeys; + } else { + // List of check keys that apply to value key $i + $keysWarmUp = array_merge( + $keysWarmUp, + self::prefixCacheKeys( $checkKeyOrKeys, self::$TIME_KEY_PREFIX ) + ); + } + } + + $warmupCache = $this->cache->getMulti( $keysWarmUp ); + $warmupCache += array_fill_keys( $keysWarmUp, false ); + + return $warmupCache; + } + + /** + * @return float UNIX timestamp + * @codeCoverageIgnore + */ + protected function getCurrentTime() { + if ( $this->wallClockOverride ) { + return $this->wallClockOverride; + } + + $clockTime = (float)time(); // call this first + // microtime() uses an initial gettimeofday() call added to usage clocks. + // This can severely drift from time() and the microtime() value of other threads + // due to undercounting of the amount of time elapsed. Instead of seeing the current + // time as being in the past, use the value of time(). This avoids setting cache values + // that will immediately be seen as expired and possibly cause stampedes. + return max( microtime( true ), $clockTime ); + } + + /** + * @param float|null &$time Mock UNIX timestamp for testing + * @codeCoverageIgnore + */ + public function setMockTime( &$time ) { + $this->wallClockOverride =& $time; + $this->cache->setMockTime( $time ); + } +} diff --git a/includes/libs/objectcache/wancache/WinCacheBagOStuff.php b/includes/libs/objectcache/wancache/WinCacheBagOStuff.php deleted file mode 100644 index 0e4e3fb63d..0000000000 --- a/includes/libs/objectcache/wancache/WinCacheBagOStuff.php +++ /dev/null @@ -1,158 +0,0 @@ -unserialize( $blob ); - if ( $value !== false ) { - $casToken = (string)$blob; // don't bother hashing this - } - - return $value; - } - - protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) { - if ( !wincache_lock( $key ) ) { // optimize with FIFO lock - return false; - } - - $curCasToken = null; // passed by reference - $this->doGet( $key, self::READ_LATEST, $curCasToken ); - if ( $casToken === $curCasToken ) { - $success = $this->set( $key, $value, $exptime, $flags ); - } else { - $this->logger->info( - __METHOD__ . ' failed due to race condition for {key}.', - [ 'key' => $key ] - ); - - $success = false; // mismatched or failed - } - - wincache_unlock( $key ); - - return $success; - } - - protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) { - $result = wincache_ucache_set( $key, $this->serialize( $value ), $exptime ); - - // false positive, wincache_ucache_set returns an empty array - // in some circumstances. - // @phan-suppress-next-line PhanTypeComparisonToArray - return ( $result === [] || $result === true ); - } - - public function add( $key, $value, $exptime = 0, $flags = 0 ) { - if ( wincache_ucache_exists( $key ) ) { - return false; // avoid warnings - } - - $result = wincache_ucache_add( $key, $this->serialize( $value ), $exptime ); - - // false positive, wincache_ucache_add returns an empty array - // in some circumstances. - // @phan-suppress-next-line PhanTypeComparisonToArray - return ( $result === [] || $result === true ); - } - - protected function doDelete( $key, $flags = 0 ) { - wincache_ucache_delete( $key ); - - return true; - } - - /** - * Construct a cache key. - * - * @since 1.27 - * @param string $keyspace - * @param array $args - * @return string - */ - public function makeKeyInternal( $keyspace, $args ) { - // WinCache keys have a maximum length of 150 characters. From that, - // subtract the number of characters we need for the keyspace and for - // the separator character needed for each argument. To handle some - // custom prefixes used by thing like WANObjectCache, limit to 125. - // NOTE: Same as in memcached, except the max key length there is 255. - $charsLeft = 125 - strlen( $keyspace ) - count( $args ); - - $args = array_map( - function ( $arg ) use ( &$charsLeft ) { - // 33 = 32 characters for the MD5 + 1 for the '#' prefix. - if ( $charsLeft > 33 && strlen( $arg ) > $charsLeft ) { - $arg = '#' . md5( $arg ); - } - - $charsLeft -= strlen( $arg ); - return $arg; - }, - $args - ); - - if ( $charsLeft < 0 ) { - return $keyspace . ':BagOStuff-long-key:##' . md5( implode( ':', $args ) ); - } - - return $keyspace . ':' . implode( ':', $args ); - } - - /** - * Increase stored value of $key by $value while preserving its original TTL - * @param string $key Key to increase - * @param int $value Value to add to $key (Default 1) - * @return int|bool New value or false on failure - */ - public function incr( $key, $value = 1 ) { - if ( !wincache_lock( $key ) ) { // optimize with FIFO lock - return false; - } - - $n = $this->doGet( $key ); - if ( $this->isInteger( $n ) ) { - $n = max( $n + (int)$value, 0 ); - $oldTTL = wincache_ucache_info( false, $key )["ucache_entries"][1]["ttl_seconds"]; - $this->set( $key, $n, $oldTTL ); - } else { - $n = false; - } - - wincache_unlock( $key ); - - return $n; - } -}