const ERR_RELAY = 4; // relay broadcast failed
const VALUE_KEY_PREFIX = 'WANCache:v:';
- const STASH_KEY_PREFIX = 'WANCache:s:';
+ const INTERIM_KEY_PREFIX = 'WANCache:i:';
const TIME_KEY_PREFIX = 'WANCache:t:';
const PURGE_VAL_PREFIX = 'PURGED:';
+ const VFLD_DATA = 'WOC:d'; // key to the value of versioned data
+ const VFLD_VERSION = 'WOC:v'; // key to the version of the value present
+
const MAX_PC_KEYS = 1000; // max keys to keep in process cache
const DEFAULT_PURGE_CHANNEL = 'wancache-purge';
* That method has cache slam avoiding features for hot/expensive keys.
*
* @param string $key Cache key
- * @param mixed $curTTL Approximate TTL left on the key if present [returned]
+ * @param mixed $curTTL Approximate TTL left on the key if present/tombstoned [returned]
* @param array $checkKeys List of "check" keys
+ * @param float &$asOf UNIX timestamp of cached value; null on failure [returned]
* @return mixed Value of cache key or false on failure
*/
- final public function get( $key, &$curTTL = null, array $checkKeys = [] ) {
+ final public function get( $key, &$curTTL = null, array $checkKeys = [], &$asOf = null ) {
$curTTLs = [];
- $values = $this->getMulti( [ $key ], $curTTLs, $checkKeys );
+ $asOfs = [];
+ $values = $this->getMulti( [ $key ], $curTTLs, $checkKeys, $asOfs );
$curTTL = isset( $curTTLs[$key] ) ? $curTTLs[$key] : null;
+ $asOf = isset( $asOfs[$key] ) ? $asOfs[$key] : null;
return isset( $values[$key] ) ? $values[$key] : false;
}
* @param array $curTTLs Map of (key => approximate TTL left) for existing keys [returned]
* @param array $checkKeys List of check keys to apply to all $keys. May also apply "check"
* keys to specific cache keys only by using cache keys as keys in the $checkKeys array.
+ * @param float[] &$asOfs Map of (key => UNIX timestamp of cached value; null on failure)
* @return array Map of (key => value) for keys that exist
*/
final public function getMulti(
- array $keys, &$curTTLs = [], array $checkKeys = []
+ array $keys, &$curTTLs = [], array $checkKeys = [], array &$asOfs = []
) {
$result = [];
$curTTLs = [];
+ $asOfs = [];
$vPrefixLen = strlen( self::VALUE_KEY_PREFIX );
$valueKeys = self::prefixCacheKeys( $keys, self::VALUE_KEY_PREFIX );
}
}
$curTTLs[$key] = $curTTL;
+ $asOfs[$key] = ( $value !== false ) ? $wrappedValues[$vKey][self::FLD_TIME] : null;
}
return $result;
* higher this is set, the higher the worst-case staleness can be.
* Use WANObjectCache::TSE_NONE to disable this logic.
* Default: WANObjectCache::TSE_NONE.
- * - pcTTL : process cache the value in this PHP instance with this TTL. This avoids
+ * - pcTTL: Process cache the value in this PHP instance with this TTL. This avoids
* network I/O when a key is read several times. This will not cache if the callback
* returns false however. Note that any purges will not be seen while process cached;
* since the callback should use slave DBs and they may be lagged or have snapshot
* isolation anyway, this should not typically matter.
* Default: WANObjectCache::TTL_UNCACHEABLE.
- * @return mixed Value to use for the key
+ * - version: Integer version number. This allows for callers to make breaking changes to
+ * how values are stored while maintaining compatability and correct cache purges. New
+ * versions are stored alongside older versions concurrently. Avoid storing class objects
+ * however, as this reduces compatibility (due to serialization).
+ * Default: null.
+ * @return mixed Value found or written to the key
*/
final public function getWithSetCallback( $key, $ttl, $callback, array $opts = [] ) {
$pcTTL = isset( $opts['pcTTL'] ) ? $opts['pcTTL'] : self::TTL_UNCACHEABLE;
$value = ( $pcTTL >= 0 ) ? $this->procCache->get( $key ) : false;
if ( $value === false ) {
+ unset( $opts['minTime'] ); // not a public feature
+
// Fetch the value over the network
- $value = $this->doGetWithSetCallback( $key, $ttl, $callback, $opts );
+ if ( isset( $opts['version'] ) ) {
+ $version = $opts['version'];
+ $asOf = null;
+ $cur = $this->doGetWithSetCallback(
+ $key,
+ $ttl,
+ function ( $oldValue, &$ttl, &$setOpts ) use ( $callback, $version ) {
+ $oldData = $oldValue ? $oldValue[self::VFLD_DATA] : false;
+ return [
+ self::VFLD_DATA => $callback( $oldData, $ttl, $setOpts ),
+ self::VFLD_VERSION => $version
+ ];
+ },
+ $opts,
+ $asOf
+ );
+ if ( $cur[self::VFLD_VERSION] === $version ) {
+ // Value created or existed before with version; use it
+ $value = $cur[self::VFLD_DATA];
+ } else {
+ // Value existed before with a different version; use variant key.
+ // Reflect purges to $key by requiring that this key value be newer.
+ $value = $this->doGetWithSetCallback(
+ 'cache-variant:' . md5( $key ) . ":$version",
+ $ttl,
+ $callback,
+ // Regenerate value if not newer than $key
+ [ 'version' => null, 'minTime' => $asOf ] + $opts
+ );
+ }
+ } else {
+ $value = $this->doGetWithSetCallback( $key, $ttl, $callback, $opts );
+ }
+
// Update the process cache if enabled
if ( $pcTTL >= 0 && $value !== false ) {
$this->procCache->set( $key, $value, $pcTTL );
* @param string $key
* @param integer $ttl
* @param callback $callback
- * @param array $opts
+ * @param array $opts Options map for getWithSetCallback() which also includes:
+ * - minTime: Treat values older than this UNIX timestamp as not existing. Default: null.
+ * @param float &$asOf Cache generation timestamp of returned value [returned]
* @return mixed
*/
- protected function doGetWithSetCallback( $key, $ttl, $callback, array $opts ) {
+ protected function doGetWithSetCallback( $key, $ttl, $callback, array $opts, &$asOf = null ) {
$lowTTL = isset( $opts['lowTTL'] ) ? $opts['lowTTL'] : min( self::LOW_TTL, $ttl );
$lockTSE = isset( $opts['lockTSE'] ) ? $opts['lockTSE'] : self::TSE_NONE;
$checkKeys = isset( $opts['checkKeys'] ) ? $opts['checkKeys'] : [];
+ $minTime = isset( $opts['minTime'] ) ? $opts['minTime'] : 0.0;
+ $versioned = isset( $opts['version'] );
// Get the current key value
$curTTL = null;
- $cValue = $this->get( $key, $curTTL, $checkKeys ); // current value
+ $cValue = $this->get( $key, $curTTL, $checkKeys, $asOf ); // current value
$value = $cValue; // return value
// Determine if a regeneration is desired
- if ( $value !== false && $curTTL > 0 && !$this->worthRefresh( $curTTL, $lowTTL ) ) {
+ if ( $value !== false
+ && $curTTL > 0
+ && $this->isValid( $value, $versioned, $asOf, $minTime )
+ && !$this->worthRefresh( $curTTL, $lowTTL )
+ ) {
return $value;
}
if ( $this->cache->lock( $key, 0, self::LOCK_TTL ) ) {
// Lock acquired; this thread should update the key
$lockAcquired = true;
- } elseif ( $value !== false ) {
+ } elseif ( $value !== false && $this->isValid( $value, $versioned, $asOf, $minTime ) ) {
// If it cannot be acquired; then the stale value can be used
return $value;
} else {
- // Use the stash value for tombstoned keys to reduce regeneration load.
+ // Use the INTERIM value for tombstoned keys to reduce regeneration load.
// For hot keys, either another thread has the lock or the lock failed;
- // use the stash value from the last thread that regenerated it.
- $value = $this->cache->get( self::STASH_KEY_PREFIX . $key );
- if ( $value !== false ) {
+ // use the INTERIM value from the last thread that regenerated it.
+ $wrapped = $this->cache->get( self::INTERIM_KEY_PREFIX . $key );
+ $value = $this->unwrap( $wrapped, microtime( true ) );
+ if ( $value !== false && $this->isValid( $value, $versioned, $asOf, $minTime ) ) {
+ $asOf = $wrapped[self::FLD_TIME];
+
return $value;
}
}
// Generate the new value from the callback...
$setOpts = [];
$value = call_user_func_array( $callback, [ $cValue, &$ttl, &$setOpts ] );
+ $asOf = microtime( true );
// When delete() is called, writes are write-holed by the tombstone,
- // so use a special stash key to pass the new value around threads.
+ // so use a special INTERIM key to pass the new value around threads.
if ( $useMutex && $value !== false && $ttl >= 0 ) {
$tempTTL = max( 1, (int)$lockTSE ); // set() expects seconds
- $this->cache->set( self::STASH_KEY_PREFIX . $key, $value, $tempTTL );
+ $wrapped = $this->wrap( $value, $tempTTL, $asOf );
+ $this->cache->set( self::INTERIM_KEY_PREFIX . $key, $wrapped, $tempTTL );
}
if ( $lockAcquired ) {
return mt_rand( 1, 1e9 ) <= 1e9 * $chance;
}
+ /**
+ * Check whether $value is appropriately versioned and not older than $minTime (if set)
+ *
+ * @param array $value
+ * @param bool $versioned
+ * @param float $asOf The time $value was generated
+ * @param float $minTime The last time the main value was generated (0.0 if unknown)
+ * @return bool
+ */
+ protected function isValid( $value, $versioned, $asOf, $minTime ) {
+ if ( $versioned && !isset( $value[self::VFLD_VERSION] ) ) {
+ return false;
+ } elseif ( $minTime > 0 && $asOf < $minTime ) {
+ return false;
+ }
+
+ return true;
+ }
+
/**
* Do not use this method outside WANObjectCache
*
dépôts / lhc / web / wiklou.git / blobdiff