3 * This program is free software; you can redistribute it and/or modify
4 * it under the terms of the GNU General Public License as published by
5 * the Free Software Foundation; either version 2 of the License, or
6 * (at your option) any later version.
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11 * GNU General Public License for more details.
13 * You should have received a copy of the GNU General Public License along
14 * with this program; if not, write to the Free Software Foundation, Inc.,
15 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
16 * http://www.gnu.org/copyleft/gpl.html
22 use Liuggio\StatsdClient\Factory\StatsdDataFactoryInterface
;
23 use Psr\Log\LoggerAwareInterface
;
24 use Psr\Log\LoggerInterface
;
25 use Psr\Log\NullLogger
;
28 * Multi-datacenter aware caching interface
30 * ### Using WANObjectCache
32 * All operations go to the local datacenter cache, except for delete(),
33 * touchCheckKey(), and resetCheckKey(), which broadcast to all datacenters.
35 * This class is intended for caching data from primary stores.
36 * If the get() method does not return a value, then the caller
37 * should query the new value and backfill the cache using set().
38 * The preferred way to do this logic is through getWithSetCallback().
39 * When querying the store on cache miss, the closest DB replica
40 * should be used. Try to avoid heavyweight DB master or quorum reads.
42 * To ensure consumers of the cache see new values in a timely manner,
43 * you either need to follow either the validation strategy, or the
46 * The validation strategy refers to the natural avoidance of stale data
47 * by one of the following means:
49 * - A) The cached value is immutable.
50 * If the consumer has access to an identifier that uniquely describes a value,
51 * cached value need not change. Instead, the key can change. This also allows
52 * all servers to access their perceived current version. This is important
53 * in context of multiple deployed versions of your application and/or cross-dc
54 * database replication, to ensure deterministic values without oscillation.
55 * - B) Validity is checked against the source after get().
56 * This is the inverse of A. The unique identifier is embedded inside the value
57 * and validated after on retreival. If outdated, the value is recomputed.
58 * - C) The value is cached with a modest TTL (without validation).
59 * If value recomputation is reasonably performant, and the value is allowed to
60 * be stale, one should consider using TTL only – using the value's age as
61 * method of validation.
63 * The purge strategy refers to the the approach whereby your application knows that
64 * source data has changed and can react by purging the relevant cache keys.
65 * As purges are expensive, this strategy should be avoided if possible.
66 * The simplest purge method is delete().
68 * No matter which strategy you choose, callers must not rely on updates or purges
69 * being immediately visible to other servers. It should be treated similarly as
70 * one would a database replica.
72 * The need for immediate updates should be avoided. If needed, solutions must be
73 * sought outside WANObjectCache.
75 * ### Deploying WANObjectCache
77 * There are two supported ways to set up broadcasted operations:
79 * - A) Set up mcrouter as the underlying cache backend, using a memcached BagOStuff class
80 * for the 'cache' parameter. The 'region' and 'cluster' parameters must be provided
81 * and 'mcrouterAware' must be set to `true`.
82 * Configure mcrouter as follows:
83 * - 1) Use Route Prefixing based on region (datacenter) and cache cluster.
84 * See https://github.com/facebook/mcrouter/wiki/Routing-Prefix and
85 * https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup.
86 * - 2) To increase the consistency of delete() and touchCheckKey() during cache
87 * server membership changes, you can use the OperationSelectorRoute to
88 * configure 'set' and 'delete' operations to go to all servers in the cache
89 * cluster, instead of just one server determined by hashing.
90 * See https://github.com/facebook/mcrouter/wiki/List-of-Route-Handles.
91 * - B) Set up dynomite as a cache middleware between the web servers and either memcached
92 * or redis and use it as the underlying cache backend, using a memcached BagOStuff
93 * class for the 'cache' parameter. This will broadcast all key setting operations,
94 * not just purges, which can be useful for cache warming. Writes are eventually
95 * consistent via the Dynamo replication model. See https://github.com/Netflix/dynomite.
97 * Broadcasted operations like delete() and touchCheckKey() are intended to run
98 * immediately in the local datacenter and asynchronously in remote datacenters.
100 * This means that callers in all datacenters may see older values for however many
101 * milliseconds that the purge took to reach that datacenter. As with any cache, this
102 * should not be relied on for cases where reads are used to determine writes to source
103 * (e.g. non-cache) data stores, except when reading immutable data.
105 * All values are wrapped in metadata arrays. Keys use a "WANCache:" prefix
106 * to avoid collisions with keys that are not wrapped as metadata arrays. The
107 * prefixes are as follows:
108 * - a) "WANCache:v" : used for regular value keys
109 * - b) "WANCache:i" : used for temporarily storing values of tombstoned keys
110 * - c) "WANCache:t" : used for storing timestamp "check" keys
111 * - d) "WANCache:m" : used for temporary mutex keys to avoid cache stampedes
116 class WANObjectCache
implements IExpiringStore
, LoggerAwareInterface
{
117 /** @var BagOStuff The local datacenter cache */
119 /** @var MapCacheLRU[] Map of group PHP instance caches */
120 protected $processCaches = [];
121 /** @bar bool Whether to use mcrouter key prefixing for routing */
122 protected $mcrouterAware;
123 /** @var string Physical region for mcrouter use */
125 /** @var string Cache cluster name for mcrouter use */
127 /** @var LoggerInterface */
129 /** @var StatsdDataFactoryInterface */
131 /** @var bool Whether to use "interim" caching while keys are tombstoned */
132 protected $useInterimHoldOffCaching = true;
133 /** @var callable|null Function that takes a WAN cache callback and runs it later */
134 protected $asyncHandler;
135 /** @var float Unix timestamp of the oldest possible valid values */
138 /** @var int Callback stack depth for getWithSetCallback() */
139 private $callbackDepth = 0;
140 /** @var mixed[] Temporary warm-up cache */
141 private $warmupCache = [];
142 /** @var int Key fetched */
143 private $warmupKeyMisses = 0;
145 /** @var float|null */
146 private $wallClockOverride;
148 /** Max time expected to pass between delete() and DB commit finishing */
149 const MAX_COMMIT_DELAY
= 3;
150 /** Max replication+snapshot lag before applying TTL_LAGGED or disallowing set() */
151 const MAX_READ_LAG
= 7;
152 /** Seconds to tombstone keys on delete() */
153 const HOLDOFF_TTL
= 11; // MAX_COMMIT_DELAY + MAX_READ_LAG + 1
155 /** Seconds to keep dependency purge keys around */
156 const CHECK_KEY_TTL
= self
::TTL_YEAR
;
157 /** Seconds to keep interim value keys for tombstoned keys around */
158 const INTERIM_KEY_TTL
= 1;
160 /** Seconds to keep lock keys around */
162 /** Seconds to no-op key set() calls to avoid large blob I/O stampedes */
163 const COOLOFF_TTL
= 1;
164 /** Default remaining TTL at which to consider pre-emptive regeneration */
167 /** Never consider performing "popularity" refreshes until a key reaches this age */
169 /** The time length of the "popularity" refresh window for hot keys */
171 /** Hits/second for a refresh to be expected within the "popularity" window */
172 const HIT_RATE_HIGH
= 1;
173 /** Seconds to ramp up to the "popularity" refresh chance after a key is no longer new */
174 const RAMPUP_TTL
= 30;
176 /** Idiom for getWithSetCallback() callbacks to avoid calling set() */
177 const TTL_UNCACHEABLE
= -1;
178 /** Idiom for getWithSetCallback() callbacks to 'lockTSE' logic */
180 /** Max TTL to store keys when a data sourced is lagged */
181 const TTL_LAGGED
= 30;
182 /** Idiom for delete() for "no hold-off" */
183 const HOLDOFF_NONE
= 0;
184 /** Idiom for set()/getWithSetCallback() for "do not augment the storage medium TTL" */
185 const STALE_TTL_NONE
= 0;
186 /** Idiom for set()/getWithSetCallback() for "no post-expired grace period" */
187 const GRACE_TTL_NONE
= 0;
189 /** Idiom for getWithSetCallback() for "no minimum required as-of timestamp" */
190 const MIN_TIMESTAMP_NONE
= 0.0;
192 /** Tiny negative float to use when CTL comes up >= 0 due to clock skew */
193 const TINY_NEGATIVE
= -0.000001;
194 /** Tiny positive float to use when using "minTime" to assert an inequality */
195 const TINY_POSTIVE
= 0.000001;
197 /** Milliseconds of delay after get() where set() storms are a consideration with 'lockTSE' */
198 const SET_DELAY_HIGH_MS
= 50;
199 /** Min millisecond set() backoff for keys in hold-off (far less than INTERIM_KEY_TTL) */
200 const RECENT_SET_LOW_MS
= 50;
201 /** Max millisecond set() backoff for keys in hold-off (far less than INTERIM_KEY_TTL) */
202 const RECENT_SET_HIGH_MS
= 100;
204 /** Parameter to get()/getMulti() to return extra information by reference */
205 const PASS_BY_REF
= -1;
207 /** Cache format version number */
210 const FLD_VERSION
= 0; // key to cache version number
211 const FLD_VALUE
= 1; // key to the cached value
212 const FLD_TTL
= 2; // key to the original TTL
213 const FLD_TIME
= 3; // key to the cache time
214 const FLD_FLAGS
= 4; // key to the flags bitfield (reserved number)
215 const FLD_HOLDOFF
= 5; // key to any hold-off TTL
217 const VALUE_KEY_PREFIX
= 'WANCache:v:';
218 const INTERIM_KEY_PREFIX
= 'WANCache:i:';
219 const TIME_KEY_PREFIX
= 'WANCache:t:';
220 const MUTEX_KEY_PREFIX
= 'WANCache:m:';
221 const COOLOFF_KEY_PREFIX
= 'WANCache:c:';
223 const PURGE_VAL_PREFIX
= 'PURGED:';
225 const VFLD_DATA
= 'WOC:d'; // key to the value of versioned data
226 const VFLD_VERSION
= 'WOC:v'; // key to the version of the value present
228 const PC_PRIMARY
= 'primary:1000'; // process cache name and max key count
231 * @param array $params
232 * - cache : BagOStuff object for a persistent cache
233 * - logger : LoggerInterface object
234 * - stats : StatsdDataFactoryInterface object
235 * - asyncHandler : A function that takes a callback and runs it later. If supplied,
236 * whenever a preemptive refresh would be triggered in getWithSetCallback(), the
237 * current cache value is still used instead. However, the async-handler function
238 * receives a WAN cache callback that, when run, will execute the value generation
239 * callback supplied by the getWithSetCallback() caller. The result will be saved
240 * as normal. The handler is expected to call the WAN cache callback at an opportune
241 * time (e.g. HTTP post-send), though generally within a few 100ms. [optional]
242 * - region: the current physical region. This is required when using mcrouter as the
243 * backing store proxy. [optional]
244 * - cluster: name of the cache cluster used by this WAN cache. The name must be the
245 * same in all datacenters; the ("region","cluster") tuple is what distinguishes
246 * the counterpart cache clusters among all the datacenter. The contents of
247 * https://github.com/facebook/mcrouter/wiki/Config-Files give background on this.
248 * This is required when using mcrouter as the backing store proxy. [optional]
249 * - mcrouterAware: set as true if mcrouter is the backing store proxy and mcrouter
250 * is configured to interpret /<region>/<cluster>/ key prefixes as routes. This
251 * requires that "region" and "cluster" are both set above. [optional]
252 * - epoch: lowest UNIX timestamp a value/tombstone must have to be valid. [optional]
254 public function __construct( array $params ) {
255 $this->cache
= $params['cache'];
256 $this->region
= $params['region'] ??
'main';
257 $this->cluster
= $params['cluster'] ??
'wan-main';
258 $this->mcrouterAware
= !empty( $params['mcrouterAware'] );
259 $this->epoch
= $params['epoch'] ??
1.0;
261 $this->setLogger( $params['logger'] ??
new NullLogger() );
262 $this->stats
= $params['stats'] ??
new NullStatsdDataFactory();
263 $this->asyncHandler
= $params['asyncHandler'] ??
null;
267 * @param LoggerInterface $logger
269 public function setLogger( LoggerInterface
$logger ) {
270 $this->logger
= $logger;
274 * Get an instance that wraps EmptyBagOStuff
276 * @return WANObjectCache
278 public static function newEmpty() {
279 return new static( [ 'cache' => new EmptyBagOStuff() ] );
283 * Fetch the value of a key from cache
285 * If supplied, $curTTL is set to the remaining TTL (current time left):
286 * - a) INF; if $key exists, has no TTL, and is not invalidated by $checkKeys
287 * - b) float (>=0); if $key exists, has a TTL, and is not invalidated by $checkKeys
288 * - c) float (<0); if $key is tombstoned, stale, or existing but invalidated by $checkKeys
289 * - d) null; if $key does not exist and is not tombstoned
291 * If a key is tombstoned, $curTTL will reflect the time since delete().
293 * The timestamp of $key will be checked against the last-purge timestamp
294 * of each of $checkKeys. Those $checkKeys not in cache will have the last-purge
295 * initialized to the current timestamp. If any of $checkKeys have a timestamp
296 * greater than that of $key, then $curTTL will reflect how long ago $key
297 * became invalid. Callers can use $curTTL to know when the value is stale.
298 * The $checkKeys parameter allow mass invalidations by updating a single key:
299 * - a) Each "check" key represents "last purged" of some source data
300 * - b) Callers pass in relevant "check" keys as $checkKeys in get()
301 * - c) When the source data that "check" keys represent changes,
302 * the touchCheckKey() method is called on them
304 * Source data entities might exists in a DB that uses snapshot isolation
305 * (e.g. the default REPEATABLE-READ in innoDB). Even for mutable data, that
306 * isolation can largely be maintained by doing the following:
307 * - a) Calling delete() on entity change *and* creation, before DB commit
308 * - b) Keeping transaction duration shorter than the delete() hold-off TTL
309 * - c) Disabling interim key caching via useInterimHoldOffCaching() before get() calls
311 * However, pre-snapshot values might still be seen if an update was made
312 * in a remote datacenter but the purge from delete() didn't relay yet.
314 * Consider using getWithSetCallback() instead of get() and set() cycles.
315 * That method has cache slam avoiding features for hot/expensive keys.
317 * Pass $info as WANObjectCache::PASS_BY_REF to transform it into a cache key info map.
318 * This map includes the following metadata:
319 * - asOf: UNIX timestamp of the value or null if the key is nonexistant
320 * - tombAsOf: UNIX timestamp of the tombstone or null if the key is not tombstoned
321 * - lastCKPurge: UNIX timestamp of the highest check key or null if none provided
323 * Otherwise, $info will transform into the cached value timestamp.
325 * @param string $key Cache key made from makeKey() or makeGlobalKey()
326 * @param mixed|null &$curTTL Approximate TTL left on the key if present/tombstoned [returned]
327 * @param array $checkKeys List of "check" keys
328 * @param mixed|null &$info Key info if WANObjectCache::PASS_BY_REF [returned]
329 * @return mixed Value of cache key or false on failure
331 final public function get(
332 $key, &$curTTL = null, array $checkKeys = [], &$info = null
334 $curTTLs = self
::PASS_BY_REF
;
335 $infoByKey = self
::PASS_BY_REF
;
336 $values = $this->getMulti( [ $key ], $curTTLs, $checkKeys, $infoByKey );
337 $curTTL = $curTTLs[$key] ??
null;
338 if ( $info === self
::PASS_BY_REF
) {
340 'asOf' => $infoByKey[$key]['asOf'] ??
null,
341 'tombAsOf' => $infoByKey[$key]['tombAsOf'] ??
null,
342 'lastCKPurge' => $infoByKey[$key]['lastCKPurge'] ??
null
345 $info = $infoByKey[$key]['asOf'] ??
null; // b/c
348 return $values[$key] ??
false;
352 * Fetch the value of several keys from cache
354 * Pass $info as WANObjectCache::PASS_BY_REF to transform it into a map of cache keys
355 * to cache key info maps, each having the same style as those of WANObjectCache::get().
356 * All the cache keys listed in $keys will have an entry.
358 * Othwerwise, $info will transform into a map of (cache key => cached value timestamp).
359 * Only the cache keys listed in $keys that exists or are tombstoned will have an entry.
361 * @see WANObjectCache::get()
363 * @param array $keys List of cache keys made from makeKey() or makeGlobalKey()
364 * @param mixed|null &$curTTLs Map of (key => TTL left) for existing/tombstoned keys [returned]
365 * @param array $checkKeys List of check keys to apply to all $keys. May also apply "check"
366 * keys to specific cache keys only by using cache keys as keys in the $checkKeys array.
367 * @param mixed|null &$info Map of (key => info) if WANObjectCache::PASS_BY_REF [returned]
368 * @return array Map of (key => value) for keys that exist and are not tombstoned
370 final public function getMulti(
373 array $checkKeys = [],
380 $vPrefixLen = strlen( self
::VALUE_KEY_PREFIX
);
381 $valueKeys = self
::prefixCacheKeys( $keys, self
::VALUE_KEY_PREFIX
);
383 $checkKeysForAll = [];
384 $checkKeysByKey = [];
386 foreach ( $checkKeys as $i => $checkKeyGroup ) {
387 $prefixed = self
::prefixCacheKeys( (array)$checkKeyGroup, self
::TIME_KEY_PREFIX
);
388 $checkKeysFlat = array_merge( $checkKeysFlat, $prefixed );
389 // Are these check keys for a specific cache key, or for all keys being fetched?
390 if ( is_int( $i ) ) {
391 $checkKeysForAll = array_merge( $checkKeysForAll, $prefixed );
393 $checkKeysByKey[$i] = $prefixed;
397 // Fetch all of the raw values
398 $keysGet = array_merge( $valueKeys, $checkKeysFlat );
399 if ( $this->warmupCache
) {
400 $wrappedValues = array_intersect_key( $this->warmupCache
, array_flip( $keysGet ) );
401 $keysGet = array_diff( $keysGet, array_keys( $wrappedValues ) ); // keys left to fetch
402 $this->warmupKeyMisses +
= count( $keysGet );
407 $wrappedValues +
= $this->cache
->getMulti( $keysGet );
409 // Time used to compare/init "check" keys (derived after getMulti() to be pessimistic)
410 $now = $this->getCurrentTime();
412 // Collect timestamps from all "check" keys
413 $purgeValuesForAll = $this->processCheckKeys( $checkKeysForAll, $wrappedValues, $now );
414 $purgeValuesByKey = [];
415 foreach ( $checkKeysByKey as $cacheKey => $checks ) {
416 $purgeValuesByKey[$cacheKey] =
417 $this->processCheckKeys( $checks, $wrappedValues, $now );
420 // Get the main cache value for each key and validate them
421 foreach ( $valueKeys as $vKey ) {
422 $key = substr( $vKey, $vPrefixLen ); // unprefix
423 list( $value, $curTTL, $asOf, $tombAsOf ) = isset( $wrappedValues[$vKey] )
424 ?
$this->unwrap( $wrappedValues[$vKey], $now )
425 : [ false, null, null, null ]; // not found
426 // Force dependent keys to be seen as stale for a while after purging
427 // to reduce race conditions involving stale data getting cached
428 $purgeValues = $purgeValuesForAll;
429 if ( isset( $purgeValuesByKey[$key] ) ) {
430 $purgeValues = array_merge( $purgeValues, $purgeValuesByKey[$key] );
433 $lastCKPurge = null; // timestamp of the highest check key
434 foreach ( $purgeValues as $purge ) {
435 $lastCKPurge = max( $purge[self
::FLD_TIME
], $lastCKPurge );
436 $safeTimestamp = $purge[self
::FLD_TIME
] +
$purge[self
::FLD_HOLDOFF
];
437 if ( $value !== false && $safeTimestamp >= $asOf ) {
438 // How long ago this value was invalidated by *this* check key
439 $ago = min( $purge[self
::FLD_TIME
] - $now, self
::TINY_NEGATIVE
);
440 // How long ago this value was invalidated by *any* known check key
441 $curTTL = min( $curTTL, $ago );
445 if ( $value !== false ) {
446 $result[$key] = $value;
448 if ( $curTTL !== null ) {
449 $curTTLs[$key] = $curTTL;
452 $infoByKey[$key] = ( $info === self
::PASS_BY_REF
)
453 ?
[ 'asOf' => $asOf, 'tombAsOf' => $tombAsOf, 'lastCKPurge' => $lastCKPurge ]
464 * @param array $timeKeys List of prefixed time check keys
465 * @param array $wrappedValues
467 * @return array List of purge value arrays
469 private function processCheckKeys( array $timeKeys, array $wrappedValues, $now ) {
471 foreach ( $timeKeys as $timeKey ) {
472 $purge = isset( $wrappedValues[$timeKey] )
473 ?
$this->parsePurgeValue( $wrappedValues[$timeKey] )
475 if ( $purge === false ) {
476 // Key is not set or malformed; regenerate
477 $newVal = $this->makePurgeValue( $now, self
::HOLDOFF_TTL
);
478 $this->cache
->add( $timeKey, $newVal, self
::CHECK_KEY_TTL
);
479 $purge = $this->parsePurgeValue( $newVal );
481 $purgeValues[] = $purge;
487 * Set the value of a key in cache
489 * Simply calling this method when source data changes is not valid because
490 * the changes do not replicate to the other WAN sites. In that case, delete()
491 * should be used instead. This method is intended for use on cache misses.
493 * If the data was read from a snapshot-isolated transactions (e.g. the default
494 * REPEATABLE-READ in innoDB), use 'since' to avoid the following race condition:
496 * - b) T2 updates a row, calls delete(), and commits
497 * - c) The HOLDOFF_TTL passes, expiring the delete() tombstone
498 * - d) T1 reads the row and calls set() due to a cache miss
499 * - e) Stale value is stuck in cache
501 * Setting 'lag' and 'since' help avoids keys getting stuck in stale states.
503 * Be aware that this does not update the process cache for getWithSetCallback()
504 * callers. Keys accessed via that method are not generally meant to also be set
505 * using this primitive method.
507 * Do not use this method on versioned keys accessed via getWithSetCallback().
511 * $dbr = wfGetDB( DB_REPLICA );
512 * $setOpts = Database::getCacheSetOptions( $dbr );
513 * // Fetch the row from the DB
514 * $row = $dbr->selectRow( ... );
515 * $key = $cache->makeKey( 'building', $buildingId );
516 * $cache->set( $key, $row, $cache::TTL_DAY, $setOpts );
519 * @param string $key Cache key
520 * @param mixed $value
521 * @param int $ttl Seconds to live. Special values are:
522 * - WANObjectCache::TTL_INDEFINITE: Cache forever (default)
523 * @param array $opts Options map:
524 * - lag: seconds of replica DB lag. Typically, this is either the replica DB lag
525 * before the data was read or, if applicable, the replica DB lag before
526 * the snapshot-isolated transaction the data was read from started.
527 * Use false to indicate that replication is not running.
529 * - since: UNIX timestamp of the data in $value. Typically, this is either
530 * the current time the data was read or (if applicable) the time when
531 * the snapshot-isolated transaction the data was read from started.
533 * - pending: whether this data is possibly from an uncommitted write transaction.
534 * Generally, other threads should not see values from the future and
535 * they certainly should not see ones that ended up getting rolled back.
537 * - lockTSE: if excessive replication/snapshot lag is detected, then store the value
538 * with this TTL and flag it as stale. This is only useful if the reads for this key
539 * use getWithSetCallback() with "lockTSE" set. Note that if "staleTTL" is set
540 * then it will still add on to this TTL in the excessive lag scenario.
541 * Default: WANObjectCache::TSE_NONE
542 * - staleTTL: seconds to keep the key around if it is stale. The get()/getMulti()
543 * methods return such stale values with a $curTTL of 0, and getWithSetCallback()
544 * will call the regeneration callback in such cases, passing in the old value
545 * and its as-of time to the callback. This is useful if adaptiveTTL() is used
546 * on the old value's as-of time when it is verified as still being correct.
547 * Default: WANObjectCache::STALE_TTL_NONE.
548 * - creating: optimize for the case where the key does not already exist.
550 * @note Options added in 1.28: staleTTL
551 * @note Options added in 1.33: creating
552 * @return bool Success
554 final public function set( $key, $value, $ttl = self
::TTL_INDEFINITE
, array $opts = [] ) {
555 $now = $this->getCurrentTime();
556 $lockTSE = $opts['lockTSE'] ?? self
::TSE_NONE
;
557 $staleTTL = $opts['staleTTL'] ?? self
::STALE_TTL_NONE
;
558 $age = isset( $opts['since'] ) ?
max( 0, $now - $opts['since'] ) : 0;
559 $creating = $opts['creating'] ??
false;
560 $lag = $opts['lag'] ??
0;
562 // Do not cache potentially uncommitted data as it might get rolled back
563 if ( !empty( $opts['pending'] ) ) {
565 'Rejected set() for {cachekey} due to pending writes.',
566 [ 'cachekey' => $key ]
569 return true; // no-op the write for being unsafe
572 $logicalTTL = null; // logical TTL override
573 // Check if there's a risk of writing stale data after the purge tombstone expired
574 if ( $lag === false ||
( $lag +
$age ) > self
::MAX_READ_LAG
) {
575 // Case A: any long-running transaction
576 if ( $age > self
::MAX_READ_LAG
) {
577 if ( $lockTSE >= 0 ) {
578 // Store value as *almost* stale to avoid cache and mutex stampedes
579 $logicalTTL = self
::TTL_SECOND
;
581 'Lowered set() TTL for {cachekey} due to snapshot lag.',
582 [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ]
586 'Rejected set() for {cachekey} due to snapshot lag.',
587 [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ]
590 return true; // no-op the write for being unsafe
592 // Case B: high replication lag; lower TTL instead of ignoring all set()s
593 } elseif ( $lag === false ||
$lag > self
::MAX_READ_LAG
) {
594 if ( $lockTSE >= 0 ) {
595 $logicalTTL = min( $ttl ?
: INF
, self
::TTL_LAGGED
);
597 $ttl = min( $ttl ?
: INF
, self
::TTL_LAGGED
);
599 $this->logger
->warning(
600 'Lowered set() TTL for {cachekey} due to replication lag.',
601 [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ]
603 // Case C: medium length request with medium replication lag
605 if ( $lockTSE >= 0 ) {
606 // Store value as *almost* stale to avoid cache and mutex stampedes
607 $logicalTTL = self
::TTL_SECOND
;
609 'Lowered set() TTL for {cachekey} due to high read lag.',
610 [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ]
614 'Rejected set() for {cachekey} due to high read lag.',
615 [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ]
618 return true; // no-op the write for being unsafe
623 // Wrap that value with time/TTL/version metadata
624 $wrapped = $this->wrap( $value, $logicalTTL ?
: $ttl, $now );
625 $storeTTL = $ttl +
$staleTTL;
628 $ok = $this->cache
->add( self
::VALUE_KEY_PREFIX
. $key, $wrapped, $storeTTL );
630 $ok = $this->cache
->merge(
631 self
::VALUE_KEY_PREFIX
. $key,
632 function ( $cache, $key, $cWrapped ) use ( $wrapped ) {
633 // A string value means that it is a tombstone; do nothing in that case
634 return ( is_string( $cWrapped ) ) ?
false : $wrapped;
645 * Purge a key from all datacenters
647 * This should only be called when the underlying data (being cached)
648 * changes in a significant way. This deletes the key and starts a hold-off
649 * period where the key cannot be written to for a few seconds (HOLDOFF_TTL).
650 * This is done to avoid the following race condition:
651 * - a) Some DB data changes and delete() is called on a corresponding key
652 * - b) A request refills the key with a stale value from a lagged DB
653 * - c) The stale value is stuck there until the key is expired/evicted
655 * This is implemented by storing a special "tombstone" value at the cache
656 * key that this class recognizes; get() calls will return false for the key
657 * and any set() calls will refuse to replace tombstone values at the key.
658 * For this to always avoid stale value writes, the following must hold:
659 * - a) Replication lag is bounded to being less than HOLDOFF_TTL; or
660 * - b) If lag is higher, the DB will have gone into read-only mode already
662 * Note that set() can also be lag-aware and lower the TTL if it's high.
664 * Be aware that this does not clear the process cache. Even if it did, callbacks
665 * used by getWithSetCallback() might still return stale data in the case of either
666 * uncommitted or not-yet-replicated changes (callback generally use replica DBs).
668 * When using potentially long-running ACID transactions, a good pattern is
669 * to use a pre-commit hook to issue the delete. This means that immediately
670 * after commit, callers will see the tombstone in cache upon purge relay.
671 * It also avoids the following race condition:
672 * - a) T1 begins, changes a row, and calls delete()
673 * - b) The HOLDOFF_TTL passes, expiring the delete() tombstone
674 * - c) T2 starts, reads the row and calls set() due to a cache miss
675 * - d) T1 finally commits
676 * - e) Stale value is stuck in cache
680 * $dbw->startAtomic( __METHOD__ ); // start of request
681 * ... <execute some stuff> ...
682 * // Update the row in the DB
683 * $dbw->update( ... );
684 * $key = $cache->makeKey( 'homes', $homeId );
685 * // Purge the corresponding cache entry just before committing
686 * $dbw->onTransactionPreCommitOrIdle( function() use ( $cache, $key ) {
687 * $cache->delete( $key );
689 * ... <execute some stuff> ...
690 * $dbw->endAtomic( __METHOD__ ); // end of request
693 * The $ttl parameter can be used when purging values that have not actually changed
694 * recently. For example, a cleanup script to purge cache entries does not really need
695 * a hold-off period, so it can use HOLDOFF_NONE. Likewise for user-requested purge.
696 * Note that $ttl limits the effective range of 'lockTSE' for getWithSetCallback().
698 * If called twice on the same key, then the last hold-off TTL takes precedence. For
699 * idempotence, the $ttl should not vary for different delete() calls on the same key.
701 * @param string $key Cache key
702 * @param int $ttl Tombstone TTL; Default: WANObjectCache::HOLDOFF_TTL
703 * @return bool True if the item was purged or not found, false on failure
705 final public function delete( $key, $ttl = self
::HOLDOFF_TTL
) {
707 // Publish the purge to all datacenters
708 $ok = $this->relayDelete( self
::VALUE_KEY_PREFIX
. $key );
710 // Publish the purge to all datacenters
711 $ok = $this->relayPurge( self
::VALUE_KEY_PREFIX
. $key, $ttl, self
::HOLDOFF_NONE
);
714 $kClass = $this->determineKeyClassForStats( $key );
715 $this->stats
->increment( "wanobjectcache.$kClass.delete." . ( $ok ?
'ok' : 'error' ) );
721 * Fetch the value of a timestamp "check" key
723 * The key will be *initialized* to the current time if not set,
724 * so only call this method if this behavior is actually desired
726 * The timestamp can be used to check whether a cached value is valid.
727 * Callers should not assume that this returns the same timestamp in
728 * all datacenters due to relay delays.
730 * The level of staleness can roughly be estimated from this key, but
731 * if the key was evicted from cache, such calculations may show the
732 * time since expiry as ~0 seconds.
734 * Note that "check" keys won't collide with other regular keys.
737 * @return float UNIX timestamp
739 final public function getCheckKeyTime( $key ) {
740 return $this->getMultiCheckKeyTime( [ $key ] )[$key];
744 * Fetch the values of each timestamp "check" key
746 * This works like getCheckKeyTime() except it takes a list of keys
747 * and returns a map of timestamps instead of just that of one key
749 * This might be useful if both:
750 * - a) a class of entities each depend on hundreds of other entities
751 * - b) these other entities are depended upon by millions of entities
753 * The later entities can each use a "check" key to invalidate their dependee entities.
754 * However, it is expensive for the former entities to verify against all of the relevant
755 * "check" keys during each getWithSetCallback() call. A less expensive approach is to do
756 * these verifications only after a "time-till-verify" (TTV) has passed. This is a middle
757 * ground between using blind TTLs and using constant verification. The adaptiveTTL() method
758 * can be used to dynamically adjust the TTV. Also, the initial TTV can make use of the
759 * last-modified times of the dependant entities (either from the DB or the "check" keys).
763 * $value = $cache->getWithSetCallback(
764 * $cache->makeGlobalKey( 'wikibase-item', $id ),
765 * self::INITIAL_TTV, // initial time-till-verify
766 * function ( $oldValue, &$ttv, &$setOpts, $oldAsOf ) use ( $checkKeys, $cache ) {
767 * $now = microtime( true );
768 * // Use $oldValue if it passes max ultimate age and "check" key comparisons
770 * $oldAsOf > max( $cache->getMultiCheckKeyTime( $checkKeys ) ) &&
771 * ( $now - $oldValue['ctime'] ) <= self::MAX_CACHE_AGE
773 * // Increase time-till-verify by 50% of last time to reduce overhead
774 * $ttv = $cache->adaptiveTTL( $oldAsOf, self::MAX_TTV, self::MIN_TTV, 1.5 );
775 * // Unlike $oldAsOf, "ctime" is the ultimate age of the cached data
779 * $mtimes = []; // dependency last-modified times; passed by reference
780 * $value = [ 'data' => $this->fetchEntityData( $mtimes ), 'ctime' => $now ];
781 * // Guess time-till-change among the dependencies, e.g. 1/(total change rate)
782 * $ttc = 1 / array_sum( array_map(
783 * function ( $mtime ) use ( $now ) {
784 * return 1 / ( $mtime ? ( $now - $mtime ) : 900 );
788 * // The time-to-verify should not be overly pessimistic nor optimistic
789 * $ttv = min( max( $ttc, self::MIN_TTV ), self::MAX_TTV );
793 * [ 'staleTTL' => $cache::TTL_DAY ] // keep around to verify and re-save
797 * @see WANObjectCache::getCheckKeyTime()
798 * @see WANObjectCache::getWithSetCallback()
801 * @return float[] Map of (key => UNIX timestamp)
804 final public function getMultiCheckKeyTime( array $keys ) {
806 foreach ( $keys as $key ) {
807 $rawKeys[$key] = self
::TIME_KEY_PREFIX
. $key;
810 $rawValues = $this->cache
->getMulti( $rawKeys );
811 $rawValues +
= array_fill_keys( $rawKeys, false );
814 foreach ( $rawKeys as $key => $rawKey ) {
815 $purge = $this->parsePurgeValue( $rawValues[$rawKey] );
816 if ( $purge !== false ) {
817 $time = $purge[self
::FLD_TIME
];
819 // Casting assures identical floats for the next getCheckKeyTime() calls
820 $now = (string)$this->getCurrentTime();
823 $this->makePurgeValue( $now, self
::HOLDOFF_TTL
),
829 $times[$key] = $time;
836 * Purge a "check" key from all datacenters, invalidating keys that use it
838 * This should only be called when the underlying data (being cached)
839 * changes in a significant way, and it is impractical to call delete()
840 * on all keys that should be changed. When get() is called on those
841 * keys, the relevant "check" keys must be supplied for this to work.
843 * The "check" key essentially represents a last-modified time of an entity.
844 * When the key is touched, the timestamp will be updated to the current time.
845 * Keys using the "check" key via get(), getMulti(), or getWithSetCallback() will
846 * be invalidated. This approach is useful if many keys depend on a single entity.
848 * The timestamp of the "check" key is treated as being HOLDOFF_TTL seconds in the
849 * future by get*() methods in order to avoid race conditions where keys are updated
850 * with stale values (e.g. from a lagged replica DB). A high TTL is set on the "check"
851 * key, making it possible to know the timestamp of the last change to the corresponding
852 * entities in most cases. This might use more cache space than resetCheckKey().
854 * When a few important keys get a large number of hits, a high cache time is usually
855 * desired as well as "lockTSE" logic. The resetCheckKey() method is less appropriate
856 * in such cases since the "time since expiry" cannot be inferred, causing any get()
857 * after the reset to treat the key as being "hot", resulting in more stale value usage.
859 * Note that "check" keys won't collide with other regular keys.
861 * @see WANObjectCache::get()
862 * @see WANObjectCache::getWithSetCallback()
863 * @see WANObjectCache::resetCheckKey()
865 * @param string $key Cache key
866 * @param int $holdoff HOLDOFF_TTL or HOLDOFF_NONE constant
867 * @return bool True if the item was purged or not found, false on failure
869 final public function touchCheckKey( $key, $holdoff = self
::HOLDOFF_TTL
) {
870 // Publish the purge to all datacenters
871 $ok = $this->relayPurge( self
::TIME_KEY_PREFIX
. $key, self
::CHECK_KEY_TTL
, $holdoff );
873 $kClass = $this->determineKeyClassForStats( $key );
874 $this->stats
->increment( "wanobjectcache.$kClass.ck_touch." . ( $ok ?
'ok' : 'error' ) );
880 * Delete a "check" key from all datacenters, invalidating keys that use it
882 * This is similar to touchCheckKey() in that keys using it via get(), getMulti(),
883 * or getWithSetCallback() will be invalidated. The differences are:
884 * - a) The "check" key will be deleted from all caches and lazily
885 * re-initialized when accessed (rather than set everywhere)
886 * - b) Thus, dependent keys will be known to be stale, but not
887 * for how long (they are treated as "just" purged), which
888 * effects any lockTSE logic in getWithSetCallback()
889 * - c) Since "check" keys are initialized only on the server the key hashes
890 * to, any temporary ejection of that server will cause the value to be
891 * seen as purged as a new server will initialize the "check" key.
893 * The advantage here is that the "check" keys, which have high TTLs, will only
894 * be created when a get*() method actually uses that key. This is better when
895 * a large number of "check" keys are invalided in a short period of time.
897 * Note that "check" keys won't collide with other regular keys.
899 * @see WANObjectCache::get()
900 * @see WANObjectCache::getWithSetCallback()
901 * @see WANObjectCache::touchCheckKey()
903 * @param string $key Cache key
904 * @return bool True if the item was purged or not found, false on failure
906 final public function resetCheckKey( $key ) {
907 // Publish the purge to all datacenters
908 $ok = $this->relayDelete( self
::TIME_KEY_PREFIX
. $key );
910 $kClass = $this->determineKeyClassForStats( $key );
911 $this->stats
->increment( "wanobjectcache.$kClass.ck_reset." . ( $ok ?
'ok' : 'error' ) );
917 * Method to fetch/regenerate cache keys
919 * On cache miss, the key will be set to the callback result via set()
920 * (unless the callback returns false) and that result will be returned.
921 * The arguments supplied to the callback are:
922 * - $oldValue : current cache value or false if not present
923 * - &$ttl : a reference to the TTL which can be altered
924 * - &$setOpts : a reference to options for set() which can be altered
925 * - $oldAsOf : generation UNIX timestamp of $oldValue or null if not present (since 1.28)
927 * It is strongly recommended to set the 'lag' and 'since' fields to avoid race conditions
928 * that can cause stale values to get stuck at keys. Usually, callbacks ignore the current
929 * value, but it can be used to maintain "most recent X" values that come from time or
930 * sequence based source data, provided that the "as of" id/time is tracked. Note that
931 * preemptive regeneration and $checkKeys can result in a non-false current value.
933 * Usage of $checkKeys is similar to get() and getMulti(). However, rather than the caller
934 * having to inspect a "current time left" variable (e.g. $curTTL, $curTTLs), a cache
935 * regeneration will automatically be triggered using the callback.
937 * The $ttl argument and "hotTTR" option (in $opts) use time-dependant randomization
938 * to avoid stampedes. Keys that are slow to regenerate and either heavily used
939 * or subject to explicit (unpredictable) purges, may need additional mechanisms.
940 * The simplest way to avoid stampedes for such keys is to use 'lockTSE' (in $opts).
941 * If explicit purges are needed, also:
942 * - a) Pass $key into $checkKeys
943 * - b) Use touchCheckKey( $key ) instead of delete( $key )
945 * Example usage (typical key):
947 * $catInfo = $cache->getWithSetCallback(
948 * // Key to store the cached value under
949 * $cache->makeKey( 'cat-attributes', $catId ),
950 * // Time-to-live (in seconds)
951 * $cache::TTL_MINUTE,
952 * // Function that derives the new key value
953 * function ( $oldValue, &$ttl, array &$setOpts ) {
954 * $dbr = wfGetDB( DB_REPLICA );
955 * // Account for any snapshot/replica DB lag
956 * $setOpts += Database::getCacheSetOptions( $dbr );
958 * return $dbr->selectRow( ... );
963 * Example usage (key that is expensive and hot):
965 * $catConfig = $cache->getWithSetCallback(
966 * // Key to store the cached value under
967 * $cache->makeKey( 'site-cat-config' ),
968 * // Time-to-live (in seconds)
970 * // Function that derives the new key value
971 * function ( $oldValue, &$ttl, array &$setOpts ) {
972 * $dbr = wfGetDB( DB_REPLICA );
973 * // Account for any snapshot/replica DB lag
974 * $setOpts += Database::getCacheSetOptions( $dbr );
976 * return CatConfig::newFromRow( $dbr->selectRow( ... ) );
979 * // Calling touchCheckKey() on this key invalidates the cache
980 * 'checkKeys' => [ $cache->makeKey( 'site-cat-config' ) ],
981 * // Try to only let one datacenter thread manage cache updates at a time
983 * // Avoid querying cache servers multiple times in a web request
984 * 'pcTTL' => $cache::TTL_PROC_LONG
989 * Example usage (key with dynamic dependencies):
991 * $catState = $cache->getWithSetCallback(
992 * // Key to store the cached value under
993 * $cache->makeKey( 'cat-state', $cat->getId() ),
994 * // Time-to-live (seconds)
996 * // Function that derives the new key value
997 * function ( $oldValue, &$ttl, array &$setOpts ) {
998 * // Determine new value from the DB
999 * $dbr = wfGetDB( DB_REPLICA );
1000 * // Account for any snapshot/replica DB lag
1001 * $setOpts += Database::getCacheSetOptions( $dbr );
1003 * return CatState::newFromResults( $dbr->select( ... ) );
1006 * // The "check" keys that represent things the value depends on;
1007 * // Calling touchCheckKey() on any of them invalidates the cache
1009 * $cache->makeKey( 'sustenance-bowls', $cat->getRoomId() ),
1010 * $cache->makeKey( 'people-present', $cat->getHouseId() ),
1011 * $cache->makeKey( 'cat-laws', $cat->getCityId() ),
1017 * Example usage (key that is expensive with too many DB dependencies for "check keys"):
1019 * $catToys = $cache->getWithSetCallback(
1020 * // Key to store the cached value under
1021 * $cache->makeKey( 'cat-toys', $catId ),
1022 * // Time-to-live (seconds)
1024 * // Function that derives the new key value
1025 * function ( $oldValue, &$ttl, array &$setOpts ) {
1026 * // Determine new value from the DB
1027 * $dbr = wfGetDB( DB_REPLICA );
1028 * // Account for any snapshot/replica DB lag
1029 * $setOpts += Database::getCacheSetOptions( $dbr );
1031 * return CatToys::newFromResults( $dbr->select( ... ) );
1034 * // Get the highest timestamp of any of the cat's toys
1035 * 'touchedCallback' => function ( $value ) use ( $catId ) {
1036 * $dbr = wfGetDB( DB_REPLICA );
1037 * $ts = $dbr->selectField( 'cat_toys', 'MAX(ct_touched)', ... );
1039 * return wfTimestampOrNull( TS_UNIX, $ts );
1041 * // Avoid DB queries for repeated access
1042 * 'pcTTL' => $cache::TTL_PROC_SHORT
1047 * Example usage (hot key holding most recent 100 events):
1049 * $lastCatActions = $cache->getWithSetCallback(
1050 * // Key to store the cached value under
1051 * $cache->makeKey( 'cat-last-actions', 100 ),
1052 * // Time-to-live (in seconds)
1054 * // Function that derives the new key value
1055 * function ( $oldValue, &$ttl, array &$setOpts ) {
1056 * $dbr = wfGetDB( DB_REPLICA );
1057 * // Account for any snapshot/replica DB lag
1058 * $setOpts += Database::getCacheSetOptions( $dbr );
1060 * // Start off with the last cached list
1061 * $list = $oldValue ?: [];
1062 * // Fetch the last 100 relevant rows in descending order;
1063 * // only fetch rows newer than $list[0] to reduce scanning
1064 * $rows = iterator_to_array( $dbr->select( ... ) );
1065 * // Merge them and get the new "last 100" rows
1066 * return array_slice( array_merge( $new, $list ), 0, 100 );
1069 * // Try to only let one datacenter thread manage cache updates at a time
1071 * // Use a magic value when no cache value is ready rather than stampeding
1072 * 'busyValue' => 'computing'
1077 * Example usage (key holding an LRU subkey:value map; this can avoid flooding cache with
1078 * keys for an unlimited set of (constraint,situation) pairs, thereby avoiding elevated
1079 * cache evictions and wasted memory):
1081 * $catSituationTolerabilityCache = $this->cache->getWithSetCallback(
1082 * // Group by constraint ID/hash, cat family ID/hash, or something else useful
1083 * $this->cache->makeKey( 'cat-situation-tolerability-checks', $groupKey ),
1084 * WANObjectCache::TTL_DAY, // rarely used groups should fade away
1085 * // The $scenarioKey format is $constraintId:<ID/hash of $situation>
1086 * function ( $cacheMap ) use ( $scenarioKey, $constraintId, $situation ) {
1087 * $lruCache = MapCacheLRU::newFromArray( $cacheMap ?: [], self::CACHE_SIZE );
1088 * $result = $lruCache->get( $scenarioKey ); // triggers LRU bump if present
1089 * if ( $result === null || $this->isScenarioResultExpired( $result ) ) {
1090 * $result = $this->checkScenarioTolerability( $constraintId, $situation );
1091 * $lruCache->set( $scenarioKey, $result, 3 / 8 );
1093 * // Save the new LRU cache map and reset the map's TTL
1094 * return $lruCache->toArray();
1097 * // Once map is > 1 sec old, consider refreshing
1099 * // Update within 5 seconds after "ageNew" given a 1hz cache check rate
1101 * // Avoid querying cache servers multiple times in a request; this also means
1102 * // that a request can only alter the value of any given constraint key once
1103 * 'pcTTL' => WANObjectCache::TTL_PROC_LONG
1106 * $tolerability = isset( $catSituationTolerabilityCache[$scenarioKey] )
1107 * ? $catSituationTolerabilityCache[$scenarioKey]
1108 * : $this->checkScenarioTolerability( $constraintId, $situation );
1111 * @see WANObjectCache::get()
1112 * @see WANObjectCache::set()
1114 * @param string $key Cache key made from makeKey() or makeGlobalKey()
1115 * @param int $ttl Seconds to live for key updates. Special values are:
1116 * - WANObjectCache::TTL_INDEFINITE: Cache forever (subject to LRU-style evictions)
1117 * - WANObjectCache::TTL_UNCACHEABLE: Do not cache (if the key exists, it is not deleted)
1118 * @param callable $callback Value generation function
1119 * @param array $opts Options map:
1120 * - checkKeys: List of "check" keys. The key at $key will be seen as stale when either
1121 * touchCheckKey() or resetCheckKey() is called on any of the keys in this list. This
1122 * is useful if thousands or millions of keys depend on the same entity. The entity can
1123 * simply have its "check" key updated whenever the entity is modified.
1125 * - graceTTL: If the key is invalidated (by "checkKeys"/"touchedCallback") less than this
1126 * many seconds ago, consider reusing the stale value. The odds of a refresh becomes
1127 * more likely over time, becoming certain once the grace period is reached. This can
1128 * reduce traffic spikes when millions of keys are compared to the same "check" key and
1129 * touchCheckKey() or resetCheckKey() is called on that "check" key. This option is not
1130 * useful for avoiding traffic spikes in the case of the key simply expiring on account
1131 * of its TTL (use "lowTTL" instead).
1132 * Default: WANObjectCache::GRACE_TTL_NONE.
1133 * - lockTSE: If the key is tombstoned or invalidated (by "checkKeys"/"touchedCallback")
1134 * less than this many seconds ago, try to have a single thread handle cache regeneration
1135 * at any given time. Other threads will use stale values if possible. If, on miss,
1136 * the time since expiration is low, the assumption is that the key is hot and that a
1137 * stampede is worth avoiding. Note that if the key falls out of cache then concurrent
1138 * threads will all run the callback on cache miss until the value is saved in cache.
1139 * The only stampede protection in that case is from duplicate cache sets when the
1140 * callback takes longer than WANObjectCache::SET_DELAY_HIGH_MS milliseconds; consider
1141 * using "busyValue" if such stampedes are a problem. Note that the higher "lockTSE" is
1142 * set, the higher the worst-case staleness of returned values can be. Also note that
1143 * this option does not by itself handle the case of the key simply expiring on account
1144 * of its TTL, so make sure that "lowTTL" is not disabled when using this option. Avoid
1145 * combining this option with delete() as it can always cause a stampede due to their
1146 * being no stale value available until after a thread completes the callback.
1147 * Use WANObjectCache::TSE_NONE to disable this logic.
1148 * Default: WANObjectCache::TSE_NONE.
1149 * - busyValue: If no value exists and another thread is currently regenerating it, use this
1150 * as a fallback value (or a callback to generate such a value). This assures that cache
1151 * stampedes cannot happen if the value falls out of cache. This can be used as insurance
1152 * against cache regeneration becoming very slow for some reason (greater than the TTL).
1154 * - pcTTL: Process cache the value in this PHP instance for this many seconds. This avoids
1155 * network I/O when a key is read several times. This will not cache when the callback
1156 * returns false, however. Note that any purges will not be seen while process cached;
1157 * since the callback should use replica DBs and they may be lagged or have snapshot
1158 * isolation anyway, this should not typically matter.
1159 * Default: WANObjectCache::TTL_UNCACHEABLE.
1160 * - pcGroup: Process cache group to use instead of the primary one. If set, this must be
1161 * of the format ALPHANUMERIC_NAME:MAX_KEY_SIZE, e.g. "mydata:10". Use this for storing
1162 * large values, small yet numerous values, or some values with a high cost of eviction.
1163 * It is generally preferable to use a class constant when setting this value.
1164 * This has no effect unless pcTTL is used.
1165 * Default: WANObjectCache::PC_PRIMARY.
1166 * - version: Integer version number. This lets callers make breaking changes to the format
1167 * of cached values without causing problems for sites that use non-instantaneous code
1168 * deployments. Old and new code will recognize incompatible versions and purges from
1169 * both old and new code will been seen by each other. When this method encounters an
1170 * incompatibly versioned value at the provided key, a "variant key" will be used for
1171 * reading from and saving to cache. The variant key is specific to the key and version
1172 * number provided to this method. If the variant key value is older than that of the
1173 * provided key, or the provided key is non-existant, then the variant key will be seen
1174 * as non-existant. Therefore, delete() calls invalidate the provided key's variant keys.
1175 * The "checkKeys" and "touchedCallback" options still apply to variant keys as usual.
1176 * Avoid storing class objects, as this reduces compatibility (due to serialization).
1178 * - minAsOf: Reject values if they were generated before this UNIX timestamp.
1179 * This is useful if the source of a key is suspected of having possibly changed
1180 * recently, and the caller wants any such changes to be reflected.
1181 * Default: WANObjectCache::MIN_TIMESTAMP_NONE.
1182 * - hotTTR: Expected time-till-refresh (TTR) in seconds for keys that average ~1 hit per
1183 * second (e.g. 1Hz). Keys with a hit rate higher than 1Hz will refresh sooner than this
1184 * TTR and vise versa. Such refreshes won't happen until keys are "ageNew" seconds old.
1185 * This uses randomization to avoid triggering cache stampedes. The TTR is useful at
1186 * reducing the impact of missed cache purges, since the effect of a heavily referenced
1187 * key being stale is worse than that of a rarely referenced key. Unlike simply lowering
1188 * $ttl, seldomly used keys are largely unaffected by this option, which makes it
1189 * possible to have a high hit rate for the "long-tail" of less-used keys.
1190 * Default: WANObjectCache::HOT_TTR.
1191 * - lowTTL: Consider pre-emptive updates when the current TTL (seconds) of the key is less
1192 * than this. It becomes more likely over time, becoming certain once the key is expired.
1193 * This helps avoid cache stampedes that might be triggered due to the key expiring.
1194 * Default: WANObjectCache::LOW_TTL.
1195 * - ageNew: Consider popularity refreshes only once a key reaches this age in seconds.
1196 * Default: WANObjectCache::AGE_NEW.
1197 * - staleTTL: Seconds to keep the key around if it is stale. This means that on cache
1198 * miss the callback may get $oldValue/$oldAsOf values for keys that have already been
1199 * expired for this specified time. This is useful if adaptiveTTL() is used on the old
1200 * value's as-of time when it is verified as still being correct.
1201 * Default: WANObjectCache::STALE_TTL_NONE
1202 * - touchedCallback: A callback that takes the current value and returns a UNIX timestamp
1203 * indicating the last time a dynamic dependency changed. Null can be returned if there
1204 * are no relevant dependency changes to check. This can be used to check against things
1205 * like last-modified times of files or DB timestamp fields. This should generally not be
1206 * used for small and easily queried values in a DB if the callback itself ends up doing
1207 * a similarly expensive DB query to check a timestamp. Usages of this option makes the
1208 * most sense for values that are moderately to highly expensive to regenerate and easy
1209 * to query for dependency timestamps. The use of "pcTTL" reduces timestamp queries.
1211 * @return mixed Value found or written to the key
1212 * @note Options added in 1.28: version, busyValue, hotTTR, ageNew, pcGroup, minAsOf
1213 * @note Options added in 1.31: staleTTL, graceTTL
1214 * @note Options added in 1.33: touchedCallback
1215 * @note Callable type hints are not used to avoid class-autoloading
1217 final public function getWithSetCallback( $key, $ttl, $callback, array $opts = [] ) {
1218 $pcTTL = $opts['pcTTL'] ?? self
::TTL_UNCACHEABLE
;
1220 // Try the process cache if enabled and the cache callback is not within a cache callback.
1221 // Process cache use in nested callbacks is not lag-safe with regard to HOLDOFF_TTL since
1222 // the in-memory value is further lagged than the shared one since it uses a blind TTL.
1223 if ( $pcTTL >= 0 && $this->callbackDepth
== 0 ) {
1224 $group = $opts['pcGroup'] ?? self
::PC_PRIMARY
;
1225 $procCache = $this->getProcessCache( $group );
1226 $value = $procCache->has( $key, $pcTTL ) ?
$procCache->get( $key ) : false;
1232 if ( $value === false ) {
1233 // Fetch the value over the network
1234 if ( isset( $opts['version'] ) ) {
1235 $version = $opts['version'];
1237 $cur = $this->doGetWithSetCallback(
1240 function ( $oldValue, &$ttl, &$setOpts, $oldAsOf )
1241 use ( $callback, $version ) {
1242 if ( is_array( $oldValue )
1243 && array_key_exists( self
::VFLD_DATA
, $oldValue )
1244 && array_key_exists( self
::VFLD_VERSION
, $oldValue )
1245 && $oldValue[self
::VFLD_VERSION
] === $version
1247 $oldData = $oldValue[self
::VFLD_DATA
];
1249 // VFLD_DATA is not set if an old, unversioned, key is present
1255 self
::VFLD_DATA
=> $callback( $oldData, $ttl, $setOpts, $oldAsOf ),
1256 self
::VFLD_VERSION
=> $version
1262 if ( $cur[self
::VFLD_VERSION
] === $version ) {
1263 // Value created or existed before with version; use it
1264 $value = $cur[self
::VFLD_DATA
];
1266 // Value existed before with a different version; use variant key.
1267 // Reflect purges to $key by requiring that this key value be newer.
1268 $value = $this->doGetWithSetCallback(
1269 $this->makeGlobalKey( 'WANCache-key-variant', md5( $key ), $version ),
1272 // Regenerate value if not newer than $key
1273 [ 'version' => null, 'minAsOf' => $asOf ] +
$opts
1277 $value = $this->doGetWithSetCallback( $key, $ttl, $callback, $opts );
1280 // Update the process cache if enabled
1281 if ( $procCache && $value !== false ) {
1282 $procCache->set( $key, $value );
1290 * Do the actual I/O for getWithSetCallback() when needed
1292 * @see WANObjectCache::getWithSetCallback()
1294 * @param string $key
1296 * @param callable $callback
1297 * @param array $opts Options map for getWithSetCallback()
1298 * @param float|null &$asOf Cache generation timestamp of returned value [returned]
1300 * @note Callable type hints are not used to avoid class-autoloading
1302 protected function doGetWithSetCallback( $key, $ttl, $callback, array $opts, &$asOf = null ) {
1303 $lowTTL = $opts['lowTTL'] ??
min( self
::LOW_TTL
, $ttl );
1304 $lockTSE = $opts['lockTSE'] ?? self
::TSE_NONE
;
1305 $staleTTL = $opts['staleTTL'] ?? self
::STALE_TTL_NONE
;
1306 $graceTTL = $opts['graceTTL'] ?? self
::GRACE_TTL_NONE
;
1307 $checkKeys = $opts['checkKeys'] ??
[];
1308 $busyValue = $opts['busyValue'] ??
null;
1309 $popWindow = $opts['hotTTR'] ?? self
::HOT_TTR
;
1310 $ageNew = $opts['ageNew'] ?? self
::AGE_NEW
;
1311 $minTime = $opts['minAsOf'] ?? self
::MIN_TIMESTAMP_NONE
;
1312 $needsVersion = isset( $opts['version'] );
1313 $touchedCb = $opts['touchedCallback'] ??
null;
1314 $initialTime = $this->getCurrentTime();
1316 $kClass = $this->determineKeyClassForStats( $key );
1318 // Get the current key value
1319 $curTTL = self
::PASS_BY_REF
;
1320 $curInfo = self
::PASS_BY_REF
; /** @var array $curInfo */
1321 $curValue = $this->get( $key, $curTTL, $checkKeys, $curInfo );
1322 // Apply any $touchedCb invalidation timestamp to get the "last purge timestamp"
1323 list( $curTTL, $LPT ) = $this->resolveCTL( $curValue, $curTTL, $curInfo, $touchedCb );
1324 // Keep track of the best candidate value and its timestamp
1325 $value = $curValue; // return value
1326 $asOf = $curInfo['asOf']; // return value timestamp
1328 // Determine if a cached value regeneration is needed or desired
1330 $this->isValid( $value, $needsVersion, $asOf, $minTime ) &&
1331 $this->isAliveOrInGracePeriod( $curTTL, $graceTTL )
1333 $preemptiveRefresh = (
1334 $this->worthRefreshExpiring( $curTTL, $lowTTL ) ||
1335 $this->worthRefreshPopular( $asOf, $ageNew, $popWindow, $initialTime )
1338 if ( !$preemptiveRefresh ) {
1339 $this->stats
->increment( "wanobjectcache.$kClass.hit.good" );
1342 } elseif ( $this->scheduleAsyncRefresh( $key, $ttl, $callback, $opts ) ) {
1343 $this->stats
->increment( "wanobjectcache.$kClass.hit.refresh" );
1349 $isKeyTombstoned = ( $curInfo['tombAsOf'] !== null );
1350 if ( $isKeyTombstoned ) {
1351 // Get the interim key value since the key is tombstoned (write-holed)
1352 list( $value, $asOf ) = $this->getInterimValue( $key, $needsVersion, $minTime );
1353 // Update the "last purge time" since the $touchedCb timestamp depends on $value
1354 $LPT = $this->resolveTouched( $value, $LPT, $touchedCb );
1357 // Reduce mutex and cache set spam while keys are in the tombstone/holdoff period by
1358 // checking if $value was genereated by a recent thread much less than a second ago.
1360 $this->isValid( $value, $needsVersion, $asOf, $minTime, $LPT ) &&
1361 $this->isVolatileValueAgeNegligible( $initialTime - $asOf )
1363 $this->stats
->increment( "wanobjectcache.$kClass.hit.volatile" );
1368 // Decide if only one thread should handle regeneration at a time
1370 // Note that since tombstones no-op set(), $lockTSE and $curTTL cannot be used to
1371 // deduce the key hotness because |$curTTL| will always keep increasing until the
1372 // tombstone expires or is overwritten by a new tombstone. Also, even if $lockTSE
1373 // is not set, constant regeneration of a key for the tombstone lifetime might be
1374 // very expensive. Assume tombstoned keys are possibly hot in order to reduce
1375 // the risk of high regeneration load after the delete() method is called.
1377 // Assume a key is hot if requested soon ($lockTSE seconds) after invalidation.
1378 // This avoids stampedes when timestamps from $checkKeys/$touchedCb bump.
1379 ( $curTTL !== null && $curTTL <= 0 && abs( $curTTL ) <= $lockTSE ) ||
1380 // Assume a key is hot if there is no value and a busy fallback is given.
1381 // This avoids stampedes on eviction or preemptive regeneration taking too long.
1382 ( $busyValue !== null && $value === false );
1386 // Acquire a datacenter-local non-blocking lock
1387 if ( $this->cache
->add( self
::MUTEX_KEY_PREFIX
. $key, 1, self
::LOCK_TTL
) ) {
1388 // Lock acquired; this thread will recompute the value and update cache
1390 } elseif ( $this->isValid( $value, $needsVersion, $asOf, $minTime ) ) {
1391 // Lock not acquired and a stale value exists; use the stale value
1392 $this->stats
->increment( "wanobjectcache.$kClass.hit.stale" );
1396 // Lock not acquired and no stale value exists
1397 if ( $busyValue !== null ) {
1398 // Use the busy fallback value if nothing else
1399 $miss = is_infinite( $minTime ) ?
'renew' : 'miss';
1400 $this->stats
->increment( "wanobjectcache.$kClass.$miss.busy" );
1402 return is_callable( $busyValue ) ?
$busyValue() : $busyValue;
1407 if ( !is_callable( $callback ) ) {
1408 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
1411 $preCallbackTime = $this->getCurrentTime();
1412 // Generate the new value from the callback...
1414 ++
$this->callbackDepth
;
1416 $value = call_user_func_array( $callback, [ $curValue, &$ttl, &$setOpts, $asOf ] );
1418 --$this->callbackDepth
;
1420 $valueIsCacheable = ( $value !== false && $ttl >= 0 );
1422 if ( $valueIsCacheable ) {
1423 $ago = max( $this->getCurrentTime() - $initialTime, 0.0 );
1424 $this->stats
->timing( "wanobjectcache.$kClass.regen_set_delay", 1000 * $ago );
1426 if ( $isKeyTombstoned ) {
1427 if ( $this->checkAndSetCooloff( $key, $kClass, $ago, $lockTSE, $hasLock ) ) {
1428 // Use the interim key value since the key is tombstoned (write-holed)
1429 $tempTTL = max( self
::INTERIM_KEY_TTL
, (int)$lockTSE );
1430 $this->setInterimValue( $key, $value, $tempTTL, $this->getCurrentTime() );
1432 } elseif ( !$useMutex ||
$hasLock ) {
1433 if ( $this->checkAndSetCooloff( $key, $kClass, $ago, $lockTSE, $hasLock ) ) {
1434 $setOpts['creating'] = ( $curValue === false );
1435 // Save the value unless a lock-winning thread is already expected to do that
1436 $setOpts['lockTSE'] = $lockTSE;
1437 $setOpts['staleTTL'] = $staleTTL;
1438 // Use best known "since" timestamp if not provided
1439 $setOpts +
= [ 'since' => $preCallbackTime ];
1440 // Update the cache; this will fail if the key is tombstoned
1441 $this->set( $key, $value, $ttl, $setOpts );
1447 $this->cache
->changeTTL( self
::MUTEX_KEY_PREFIX
. $key, (int)$initialTime - 60 );
1450 $miss = is_infinite( $minTime ) ?
'renew' : 'miss';
1451 $this->stats
->increment( "wanobjectcache.$kClass.$miss.compute" );
1457 * @param float $age Age of volatile/interim key in seconds
1458 * @return bool Whether the age of a volatile value is negligible
1460 private function isVolatileValueAgeNegligible( $age ) {
1461 return ( $age < mt_rand( self
::RECENT_SET_LOW_MS
, self
::RECENT_SET_HIGH_MS
) / 1e3
);
1465 * @param string $key
1466 * @param string $kClass
1467 * @param float $elapsed Seconds spent regenerating the value
1468 * @param float $lockTSE
1469 * @param $hasLock bool
1470 * @return bool Whether it is OK to proceed with a key set operation
1472 private function checkAndSetCooloff( $key, $kClass, $elapsed, $lockTSE, $hasLock ) {
1473 // If $lockTSE is set, the lock was bypassed because there was no stale/interim value,
1474 // and $elapsed indicates that regeration is slow, then there is a risk of set()
1475 // stampedes with large blobs. With a typical scale-out infrastructure, CPU and query
1476 // load from $callback invocations is distributed among appservers and replica DBs,
1477 // but cache operations for a given key route to a single cache server (e.g. striped
1478 // consistent hashing).
1479 if ( $lockTSE < 0 ||
$hasLock ) {
1480 return true; // either not a priori hot or thread has the lock
1481 } elseif ( $elapsed <= self
::SET_DELAY_HIGH_MS
* 1e3
) {
1482 return true; // not enough time for threads to pile up
1485 $this->cache
->clearLastError();
1487 !$this->cache
->add( self
::COOLOFF_KEY_PREFIX
. $key, 1, self
::COOLOFF_TTL
) &&
1488 // Don't treat failures due to I/O errors as the key being in cooloff
1489 $this->cache
->getLastError() === BagOStuff
::ERR_NONE
1491 $this->stats
->increment( "wanobjectcache.$kClass.cooloff_bounce" );
1500 * @param mixed $value
1501 * @param float|null $curTTL
1502 * @param array $curInfo
1503 * @param callable|null $touchedCallback
1504 * @return array (current time left or null, UNIX timestamp of last purge or null)
1505 * @note Callable type hints are not used to avoid class-autoloading
1507 protected function resolveCTL( $value, $curTTL, $curInfo, $touchedCallback ) {
1508 if ( $touchedCallback === null ||
$value === false ) {
1509 return [ $curTTL, max( $curInfo['tombAsOf'], $curInfo['lastCKPurge'] ) ];
1512 if ( !is_callable( $touchedCallback ) ) {
1513 throw new InvalidArgumentException( "Invalid expiration callback provided." );
1516 $touched = $touchedCallback( $value );
1517 if ( $touched !== null && $touched >= $curInfo['asOf'] ) {
1518 $curTTL = min( $curTTL, self
::TINY_NEGATIVE
, $curInfo['asOf'] - $touched );
1521 return [ $curTTL, max( $curInfo['tombAsOf'], $curInfo['lastCKPurge'], $touched ) ];
1525 * @param mixed $value
1526 * @param float|null $lastPurge
1527 * @param callable|null $touchedCallback
1528 * @return float|null UNIX timestamp of last purge or null
1529 * @note Callable type hints are not used to avoid class-autoloading
1531 protected function resolveTouched( $value, $lastPurge, $touchedCallback ) {
1532 if ( $touchedCallback === null ||
$value === false ) {
1536 if ( !is_callable( $touchedCallback ) ) {
1537 throw new InvalidArgumentException( "Invalid expiration callback provided." );
1540 return max( $touchedCallback( $value ), $lastPurge );
1544 * @param string $key
1545 * @param bool $versioned
1546 * @param float $minTime
1547 * @return array (cached value or false, cached value timestamp or null)
1549 protected function getInterimValue( $key, $versioned, $minTime ) {
1550 if ( !$this->useInterimHoldOffCaching
) {
1551 return [ false, null ]; // disabled
1554 $wrapped = $this->cache
->get( self
::INTERIM_KEY_PREFIX
. $key );
1555 list( $value ) = $this->unwrap( $wrapped, $this->getCurrentTime() );
1556 $valueAsOf = $wrapped[self
::FLD_TIME
] ??
null;
1557 if ( $this->isValid( $value, $versioned, $valueAsOf, $minTime ) ) {
1558 return [ $value, $valueAsOf ];
1561 return [ false, null ];
1565 * @param string $key
1566 * @param mixed $value
1567 * @param int $tempTTL
1568 * @param float $newAsOf
1570 protected function setInterimValue( $key, $value, $tempTTL, $newAsOf ) {
1571 $wrapped = $this->wrap( $value, $tempTTL, $newAsOf );
1573 $this->cache
->merge(
1574 self
::INTERIM_KEY_PREFIX
. $key,
1575 function () use ( $wrapped ) {
1584 * Method to fetch multiple cache keys at once with regeneration
1586 * This works the same as getWithSetCallback() except:
1587 * - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys()
1588 * - b) The $callback argument expects a callback taking the following arguments:
1589 * - $id: ID of an entity to query
1590 * - $oldValue : the prior cache value or false if none was present
1591 * - &$ttl : a reference to the new value TTL in seconds
1592 * - &$setOpts : a reference to options for set() which can be altered
1593 * - $oldAsOf : generation UNIX timestamp of $oldValue or null if not present
1594 * Aside from the additional $id argument, the other arguments function the same
1595 * way they do in getWithSetCallback().
1596 * - c) The return value is a map of (cache key => value) in the order of $keyedIds
1598 * @see WANObjectCache::getWithSetCallback()
1599 * @see WANObjectCache::getMultiWithUnionSetCallback()
1603 * $rows = $cache->getMultiWithSetCallback(
1604 * // Map of cache keys to entity IDs
1605 * $cache->makeMultiKeys(
1606 * $this->fileVersionIds(),
1607 * function ( $id, WANObjectCache $cache ) {
1608 * return $cache->makeKey( 'file-version', $id );
1611 * // Time-to-live (in seconds)
1613 * // Function that derives the new key value
1614 * function ( $id, $oldValue, &$ttl, array &$setOpts ) {
1615 * $dbr = wfGetDB( DB_REPLICA );
1616 * // Account for any snapshot/replica DB lag
1617 * $setOpts += Database::getCacheSetOptions( $dbr );
1619 * // Load the row for this file
1620 * $queryInfo = File::getQueryInfo();
1621 * $row = $dbr->selectRow(
1622 * $queryInfo['tables'],
1623 * $queryInfo['fields'],
1627 * $queryInfo['joins']
1630 * return $row ? (array)$row : false;
1633 * // Process cache for 30 seconds
1635 * // Use a dedicated 500 item cache (initialized on-the-fly)
1636 * 'pcGroup' => 'file-versions:500'
1639 * $files = array_map( [ __CLASS__, 'newFromRow' ], $rows );
1642 * @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys()
1643 * @param int $ttl Seconds to live for key updates
1644 * @param callable $callback Callback the yields entity regeneration callbacks
1645 * @param array $opts Options map
1646 * @return array Map of (cache key => value) in the same order as $keyedIds
1649 final public function getMultiWithSetCallback(
1650 ArrayIterator
$keyedIds, $ttl, callable
$callback, array $opts = []
1652 $valueKeys = array_keys( $keyedIds->getArrayCopy() );
1653 $checkKeys = $opts['checkKeys'] ??
[];
1654 $pcTTL = $opts['pcTTL'] ?? self
::TTL_UNCACHEABLE
;
1656 // Load required keys into process cache in one go
1657 $this->warmupCache
= $this->getRawKeysForWarmup(
1658 $this->getNonProcessCachedKeys( $valueKeys, $opts, $pcTTL ),
1661 $this->warmupKeyMisses
= 0;
1663 // Wrap $callback to match the getWithSetCallback() format while passing $id to $callback
1664 $id = null; // current entity ID
1665 $func = function ( $oldValue, &$ttl, &$setOpts, $oldAsOf ) use ( $callback, &$id ) {
1666 return $callback( $id, $oldValue, $ttl, $setOpts, $oldAsOf );
1670 foreach ( $keyedIds as $key => $id ) { // preserve order
1671 $values[$key] = $this->getWithSetCallback( $key, $ttl, $func, $opts );
1674 $this->warmupCache
= [];
1680 * Method to fetch/regenerate multiple cache keys at once
1682 * This works the same as getWithSetCallback() except:
1683 * - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys()
1684 * - b) The $callback argument expects a callback returning a map of (ID => new value)
1685 * for all entity IDs in $ids and it takes the following arguments:
1686 * - $ids: a list of entity IDs that require cache regeneration
1687 * - &$ttls: a reference to the (entity ID => new TTL) map
1688 * - &$setOpts: a reference to options for set() which can be altered
1689 * - c) The return value is a map of (cache key => value) in the order of $keyedIds
1690 * - d) The "lockTSE" and "busyValue" options are ignored
1692 * @see WANObjectCache::getWithSetCallback()
1693 * @see WANObjectCache::getMultiWithSetCallback()
1697 * $rows = $cache->getMultiWithUnionSetCallback(
1698 * // Map of cache keys to entity IDs
1699 * $cache->makeMultiKeys(
1700 * $this->fileVersionIds(),
1701 * function ( $id, WANObjectCache $cache ) {
1702 * return $cache->makeKey( 'file-version', $id );
1705 * // Time-to-live (in seconds)
1707 * // Function that derives the new key value
1708 * function ( array $ids, array &$ttls, array &$setOpts ) {
1709 * $dbr = wfGetDB( DB_REPLICA );
1710 * // Account for any snapshot/replica DB lag
1711 * $setOpts += Database::getCacheSetOptions( $dbr );
1713 * // Load the rows for these files
1715 * $queryInfo = File::getQueryInfo();
1716 * $res = $dbr->select(
1717 * $queryInfo['tables'],
1718 * $queryInfo['fields'],
1722 * $queryInfo['joins']
1724 * foreach ( $res as $row ) {
1725 * $rows[$row->id] = $row;
1726 * $mtime = wfTimestamp( TS_UNIX, $row->timestamp );
1727 * $ttls[$row->id] = $this->adaptiveTTL( $mtime, $ttls[$row->id] );
1734 * $files = array_map( [ __CLASS__, 'newFromRow' ], $rows );
1737 * @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys()
1738 * @param int $ttl Seconds to live for key updates
1739 * @param callable $callback Callback the yields entity regeneration callbacks
1740 * @param array $opts Options map
1741 * @return array Map of (cache key => value) in the same order as $keyedIds
1744 final public function getMultiWithUnionSetCallback(
1745 ArrayIterator
$keyedIds, $ttl, callable
$callback, array $opts = []
1747 $idsByValueKey = $keyedIds->getArrayCopy();
1748 $valueKeys = array_keys( $idsByValueKey );
1749 $checkKeys = $opts['checkKeys'] ??
[];
1750 $pcTTL = $opts['pcTTL'] ?? self
::TTL_UNCACHEABLE
;
1751 unset( $opts['lockTSE'] ); // incompatible
1752 unset( $opts['busyValue'] ); // incompatible
1754 // Load required keys into process cache in one go
1755 $keysGet = $this->getNonProcessCachedKeys( $valueKeys, $opts, $pcTTL );
1756 $this->warmupCache
= $this->getRawKeysForWarmup( $keysGet, $checkKeys );
1757 $this->warmupKeyMisses
= 0;
1759 // IDs of entities known to be in need of regeneration
1762 // Find out which keys are missing/deleted/stale
1765 $curByKey = $this->getMulti( $keysGet, $curTTLs, $checkKeys, $asOfs );
1766 foreach ( $keysGet as $key ) {
1767 if ( !array_key_exists( $key, $curByKey ) ||
$curTTLs[$key] < 0 ) {
1768 $idsRegen[] = $idsByValueKey[$key];
1772 // Run the callback to populate the regeneration value map for all required IDs
1774 $newTTLsById = array_fill_keys( $idsRegen, $ttl );
1775 $newValsById = $idsRegen ?
$callback( $idsRegen, $newTTLsById, $newSetOpts ) : [];
1777 // Wrap $callback to match the getWithSetCallback() format while passing $id to $callback
1778 $id = null; // current entity ID
1779 $func = function ( $oldValue, &$ttl, &$setOpts, $oldAsOf )
1780 use ( $callback, &$id, $newValsById, $newTTLsById, $newSetOpts )
1782 if ( array_key_exists( $id, $newValsById ) ) {
1783 // Value was already regerated as expected, so use the value in $newValsById
1784 $newValue = $newValsById[$id];
1785 $ttl = $newTTLsById[$id];
1786 $setOpts = $newSetOpts;
1788 // Pre-emptive/popularity refresh and version mismatch cases are not detected
1789 // above and thus $newValsById has no entry. Run $callback on this single entity.
1790 $ttls = [ $id => $ttl ];
1791 $newValue = $callback( [ $id ], $ttls, $setOpts )[$id];
1798 // Run the cache-aside logic using warmupCache instead of persistent cache queries
1800 foreach ( $idsByValueKey as $key => $id ) { // preserve order
1801 $values[$key] = $this->getWithSetCallback( $key, $ttl, $func, $opts );
1804 $this->warmupCache
= [];
1810 * Set a key to soon expire in the local cluster if it pre-dates $purgeTimestamp
1812 * This sets stale keys' time-to-live at HOLDOFF_TTL seconds, which both avoids
1813 * broadcasting in mcrouter setups and also avoids races with new tombstones.
1815 * @param string $key Cache key
1816 * @param int $purgeTimestamp UNIX timestamp of purge
1817 * @param bool &$isStale Whether the key is stale
1818 * @return bool Success
1821 final public function reap( $key, $purgeTimestamp, &$isStale = false ) {
1822 $minAsOf = $purgeTimestamp + self
::HOLDOFF_TTL
;
1823 $wrapped = $this->cache
->get( self
::VALUE_KEY_PREFIX
. $key );
1824 if ( is_array( $wrapped ) && $wrapped[self
::FLD_TIME
] < $minAsOf ) {
1826 $this->logger
->warning( "Reaping stale value key '$key'." );
1827 $ttlReap = self
::HOLDOFF_TTL
; // avoids races with tombstone creation
1828 $ok = $this->cache
->changeTTL( self
::VALUE_KEY_PREFIX
. $key, $ttlReap );
1830 $this->logger
->error( "Could not complete reap of key '$key'." );
1842 * Set a "check" key to soon expire in the local cluster if it pre-dates $purgeTimestamp
1844 * @param string $key Cache key
1845 * @param int $purgeTimestamp UNIX timestamp of purge
1846 * @param bool &$isStale Whether the key is stale
1847 * @return bool Success
1850 final public function reapCheckKey( $key, $purgeTimestamp, &$isStale = false ) {
1851 $purge = $this->parsePurgeValue( $this->cache
->get( self
::TIME_KEY_PREFIX
. $key ) );
1852 if ( $purge && $purge[self
::FLD_TIME
] < $purgeTimestamp ) {
1854 $this->logger
->warning( "Reaping stale check key '$key'." );
1855 $ok = $this->cache
->changeTTL( self
::TIME_KEY_PREFIX
. $key, self
::TTL_SECOND
);
1857 $this->logger
->error( "Could not complete reap of check key '$key'." );
1869 * @see BagOStuff::makeKey()
1870 * @param string $class Key class
1871 * @param string|null $component [optional] Key component (starting with a key collection name)
1872 * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1875 public function makeKey( $class, $component = null ) {
1876 return $this->cache
->makeKey( ...func_get_args() );
1880 * @see BagOStuff::makeGlobalKey()
1881 * @param string $class Key class
1882 * @param string|null $component [optional] Key component (starting with a key collection name)
1883 * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1886 public function makeGlobalKey( $class, $component = null ) {
1887 return $this->cache
->makeGlobalKey( ...func_get_args() );
1891 * @param array $entities List of entity IDs
1892 * @param callable $keyFunc Callback yielding a key from (entity ID, this WANObjectCache)
1893 * @return ArrayIterator Iterator yielding (cache key => entity ID) in $entities order
1896 final public function makeMultiKeys( array $entities, callable
$keyFunc ) {
1898 foreach ( $entities as $entity ) {
1899 $map[$keyFunc( $entity, $this )] = $entity;
1902 return new ArrayIterator( $map );
1906 * Get the "last error" registered; clearLastError() should be called manually
1907 * @return int ERR_* class constant for the "last error" registry
1909 final public function getLastError() {
1910 $code = $this->cache
->getLastError();
1912 case BagOStuff
::ERR_NONE
:
1913 return self
::ERR_NONE
;
1914 case BagOStuff
::ERR_NO_RESPONSE
:
1915 return self
::ERR_NO_RESPONSE
;
1916 case BagOStuff
::ERR_UNREACHABLE
:
1917 return self
::ERR_UNREACHABLE
;
1919 return self
::ERR_UNEXPECTED
;
1924 * Clear the "last error" registry
1926 final public function clearLastError() {
1927 $this->cache
->clearLastError();
1931 * Clear the in-process caches; useful for testing
1935 public function clearProcessCache() {
1936 $this->processCaches
= [];
1940 * Enable or disable the use of brief caching for tombstoned keys
1942 * When a key is purged via delete(), there normally is a period where caching
1943 * is hold-off limited to an extremely short time. This method will disable that
1944 * caching, forcing the callback to run for any of:
1945 * - WANObjectCache::getWithSetCallback()
1946 * - WANObjectCache::getMultiWithSetCallback()
1947 * - WANObjectCache::getMultiWithUnionSetCallback()
1949 * This is useful when both:
1950 * - a) the database used by the callback is known to be up-to-date enough
1951 * for some particular purpose (e.g. replica DB has applied transaction X)
1952 * - b) the caller needs to exploit that fact, and therefore needs to avoid the
1953 * use of inherently volatile and possibly stale interim keys
1955 * @see WANObjectCache::delete()
1956 * @param bool $enabled Whether to enable interim caching
1959 final public function useInterimHoldOffCaching( $enabled ) {
1960 $this->useInterimHoldOffCaching
= $enabled;
1964 * @param int $flag ATTR_* class constant
1965 * @return int QOS_* class constant
1968 public function getQoS( $flag ) {
1969 return $this->cache
->getQoS( $flag );
1973 * Get a TTL that is higher for objects that have not changed recently
1975 * This is useful for keys that get explicit purges and DB or purge relay
1976 * lag is a potential concern (especially how it interacts with CDN cache)
1980 * // Last-modified time of page
1981 * $mtime = wfTimestamp( TS_UNIX, $page->getTimestamp() );
1982 * // Get adjusted TTL. If $mtime is 3600 seconds ago and $minTTL/$factor left at
1983 * // defaults, then $ttl is 3600 * .2 = 720. If $minTTL was greater than 720, then
1984 * // $ttl would be $minTTL. If $maxTTL was smaller than 720, $ttl would be $maxTTL.
1985 * $ttl = $cache->adaptiveTTL( $mtime, $cache::TTL_DAY );
1988 * Another use case is when there are no applicable "last modified" fields in the DB,
1989 * and there are too many dependencies for explicit purges to be viable, and the rate of
1990 * change to relevant content is unstable, and it is highly valued to have the cached value
1991 * be as up-to-date as possible.
1995 * $query = "<some complex query>";
1996 * $idListFromComplexQuery = $cache->getWithSetCallback(
1997 * $cache->makeKey( 'complex-graph-query', $hashOfQuery ),
1998 * GraphQueryClass::STARTING_TTL,
1999 * function ( $oldValue, &$ttl, array &$setOpts, $oldAsOf ) use ( $query, $cache ) {
2000 * $gdb = $this->getReplicaGraphDbConnection();
2001 * // Account for any snapshot/replica DB lag
2002 * $setOpts += GraphDatabase::getCacheSetOptions( $gdb );
2004 * $newList = iterator_to_array( $gdb->query( $query ) );
2005 * sort( $newList, SORT_NUMERIC ); // normalize
2007 * $minTTL = GraphQueryClass::MIN_TTL;
2008 * $maxTTL = GraphQueryClass::MAX_TTL;
2009 * if ( $oldValue !== false ) {
2010 * // Note that $oldAsOf is the last time this callback ran
2011 * $ttl = ( $newList === $oldValue )
2012 * // No change: cache for 150% of the age of $oldValue
2013 * ? $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, 1.5 )
2014 * // Changed: cache for 50% of the age of $oldValue
2015 * : $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, .5 );
2021 * // Keep stale values around for doing comparisons for TTL calculations.
2022 * // High values improve long-tail keys hit-rates, though might waste space.
2023 * 'staleTTL' => GraphQueryClass::GRACE_TTL
2028 * @param int|float $mtime UNIX timestamp
2029 * @param int $maxTTL Maximum TTL (seconds)
2030 * @param int $minTTL Minimum TTL (seconds); Default: 30
2031 * @param float $factor Value in the range (0,1); Default: .2
2032 * @return int Adaptive TTL
2035 public function adaptiveTTL( $mtime, $maxTTL, $minTTL = 30, $factor = 0.2 ) {
2036 if ( is_float( $mtime ) ||
ctype_digit( $mtime ) ) {
2037 $mtime = (int)$mtime; // handle fractional seconds and string integers
2040 if ( !is_int( $mtime ) ||
$mtime <= 0 ) {
2041 return $minTTL; // no last-modified time provided
2044 $age = $this->getCurrentTime() - $mtime;
2046 return (int)min( $maxTTL, max( $minTTL, $factor * $age ) );
2050 * @return int Number of warmup key cache misses last round
2053 final public function getWarmupKeyMisses() {
2054 return $this->warmupKeyMisses
;
2058 * Do the actual async bus purge of a key
2060 * This must set the key to "PURGED:<UNIX timestamp>:<holdoff>"
2062 * @param string $key Cache key
2063 * @param int $ttl How long to keep the tombstone [seconds]
2064 * @param int $holdoff HOLDOFF_* constant controlling how long to ignore sets for this key
2065 * @return bool Success
2067 protected function relayPurge( $key, $ttl, $holdoff ) {
2068 if ( $this->mcrouterAware
) {
2069 // See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup
2070 // Wildcards select all matching routes, e.g. the WAN cluster on all DCs
2071 $ok = $this->cache
->set(
2072 "/*/{$this->cluster}/{$key}",
2073 $this->makePurgeValue( $this->getCurrentTime(), self
::HOLDOFF_NONE
),
2077 // This handles the mcrouter and the single-DC case
2078 $ok = $this->cache
->set(
2080 $this->makePurgeValue( $this->getCurrentTime(), self
::HOLDOFF_NONE
),
2089 * Do the actual async bus delete of a key
2091 * @param string $key Cache key
2092 * @return bool Success
2094 protected function relayDelete( $key ) {
2095 if ( $this->mcrouterAware
) {
2096 // See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup
2097 // Wildcards select all matching routes, e.g. the WAN cluster on all DCs
2098 $ok = $this->cache
->delete( "/*/{$this->cluster}/{$key}" );
2100 // Some other proxy handles broadcasting or there is only one datacenter
2101 $ok = $this->cache
->delete( $key );
2108 * @param string $key
2110 * @param callable $callback
2111 * @param array $opts
2112 * @return bool Success
2114 private function scheduleAsyncRefresh( $key, $ttl, $callback, $opts ) {
2115 if ( !$this->asyncHandler
) {
2118 // Update the cache value later, such during post-send of an HTTP request
2119 $func = $this->asyncHandler
;
2120 $func( function () use ( $key, $ttl, $callback, $opts ) {
2121 $asOf = null; // unused
2122 $opts['minAsOf'] = INF
; // force a refresh
2123 $this->doGetWithSetCallback( $key, $ttl, $callback, $opts, $asOf );
2130 * Check if a key is fresh or in the grace window and thus due for randomized reuse
2132 * If $curTTL > 0 (e.g. not expired) this returns true. Otherwise, the chance of returning
2133 * true decrease steadily from 100% to 0% as the |$curTTL| moves from 0 to $graceTTL seconds.
2134 * This handles widely varying levels of cache access traffic.
2136 * If $curTTL <= -$graceTTL (e.g. already expired), then this returns false.
2138 * @param float $curTTL Approximate TTL left on the key if present
2139 * @param int $graceTTL Consider using stale values if $curTTL is greater than this
2142 protected function isAliveOrInGracePeriod( $curTTL, $graceTTL ) {
2143 if ( $curTTL > 0 ) {
2145 } elseif ( $graceTTL <= 0 ) {
2149 $ageStale = abs( $curTTL ); // seconds of staleness
2150 $curGTTL = ( $graceTTL - $ageStale ); // current grace-time-to-live
2151 if ( $curGTTL <= 0 ) {
2152 return false; // already out of grace period
2155 // Chance of using a stale value is the complement of the chance of refreshing it
2156 return !$this->worthRefreshExpiring( $curGTTL, $graceTTL );
2160 * Check if a key is nearing expiration and thus due for randomized regeneration
2162 * This returns false if $curTTL >= $lowTTL. Otherwise, the chance of returning true
2163 * increases steadily from 0% to 100% as the $curTTL moves from $lowTTL to 0 seconds.
2164 * This handles widely varying levels of cache access traffic.
2166 * If $curTTL <= 0 (e.g. already expired), then this returns false.
2168 * @param float $curTTL Approximate TTL left on the key if present
2169 * @param float $lowTTL Consider a refresh when $curTTL is less than this
2172 protected function worthRefreshExpiring( $curTTL, $lowTTL ) {
2173 if ( $lowTTL <= 0 ) {
2175 } elseif ( $curTTL >= $lowTTL ) {
2177 } elseif ( $curTTL <= 0 ) {
2181 $chance = ( 1 - $curTTL / $lowTTL );
2183 return mt_rand( 1, 1e9
) <= 1e9
* $chance;
2187 * Check if a key is due for randomized regeneration due to its popularity
2189 * This is used so that popular keys can preemptively refresh themselves for higher
2190 * consistency (especially in the case of purge loss/delay). Unpopular keys can remain
2191 * in cache with their high nominal TTL. This means popular keys keep good consistency,
2192 * whether the data changes frequently or not, and long-tail keys get to stay in cache
2193 * and get hits too. Similar to worthRefreshExpiring(), randomization is used.
2195 * @param float $asOf UNIX timestamp of the value
2196 * @param int $ageNew Age of key when this might recommend refreshing (seconds)
2197 * @param int $timeTillRefresh Age of key when it should be refreshed if popular (seconds)
2198 * @param float $now The current UNIX timestamp
2201 protected function worthRefreshPopular( $asOf, $ageNew, $timeTillRefresh, $now ) {
2202 if ( $ageNew < 0 ||
$timeTillRefresh <= 0 ) {
2206 $age = $now - $asOf;
2207 $timeOld = $age - $ageNew;
2208 if ( $timeOld <= 0 ) {
2212 // Lifecycle is: new, ramp-up refresh chance, full refresh chance.
2213 // Note that the "expected # of refreshes" for the ramp-up time range is half of what it
2214 // would be if P(refresh) was at its full value during that time range.
2215 $refreshWindowSec = max( $timeTillRefresh - $ageNew - self
::RAMPUP_TTL
/ 2, 1 );
2216 // P(refresh) * (# hits in $refreshWindowSec) = (expected # of refreshes)
2217 // P(refresh) * ($refreshWindowSec * $popularHitsPerSec) = 1
2218 // P(refresh) = 1/($refreshWindowSec * $popularHitsPerSec)
2219 $chance = 1 / ( self
::HIT_RATE_HIGH
* $refreshWindowSec );
2221 // Ramp up $chance from 0 to its nominal value over RAMPUP_TTL seconds to avoid stampedes
2222 $chance *= ( $timeOld <= self
::RAMPUP_TTL
) ?
$timeOld / self
::RAMPUP_TTL
: 1;
2224 return mt_rand( 1, 1e9
) <= 1e9
* $chance;
2228 * Check if $value is not false, versioned (if needed), and not older than $minTime (if set)
2230 * @param array|bool $value
2231 * @param bool $versioned
2232 * @param float $asOf The time $value was generated
2233 * @param float $minTime The last time the main value was generated (0.0 if unknown)
2234 * @param float|null $purgeTime The last time the value was invalidated
2237 protected function isValid( $value, $versioned, $asOf, $minTime, $purgeTime = null ) {
2238 // Avoid reading any key not generated after the latest delete() or touch
2239 $safeMinTime = max( $minTime, $purgeTime + self
::TINY_POSTIVE
);
2241 if ( $value === false ) {
2243 } elseif ( $versioned && !isset( $value[self
::VFLD_VERSION
] ) ) {
2245 } elseif ( $safeMinTime > 0 && $asOf < $minTime ) {
2253 * Do not use this method outside WANObjectCache
2255 * @param mixed $value
2256 * @param int $ttl [0=forever]
2257 * @param float $now Unix Current timestamp just before calling set()
2260 protected function wrap( $value, $ttl, $now ) {
2262 self
::FLD_VERSION
=> self
::VERSION
,
2263 self
::FLD_VALUE
=> $value,
2264 self
::FLD_TTL
=> $ttl,
2265 self
::FLD_TIME
=> $now
2270 * Do not use this method outside WANObjectCache
2272 * The cached value will be false if absent/tombstoned/malformed
2274 * @param array|string|bool $wrapped
2275 * @param float $now Unix Current timestamp (preferrably pre-query)
2276 * @return array (cached value or false, current TTL, value timestamp, tombstone timestamp)
2278 protected function unwrap( $wrapped, $now ) {
2279 // Check if the value is a tombstone
2280 $purge = $this->parsePurgeValue( $wrapped );
2281 if ( $purge !== false ) {
2282 // Purged values should always have a negative current $ttl
2283 $curTTL = min( $purge[self
::FLD_TIME
] - $now, self
::TINY_NEGATIVE
);
2284 return [ false, $curTTL, null, $purge[self
::FLD_TIME
] ];
2287 if ( !is_array( $wrapped ) // not found
2288 ||
!isset( $wrapped[self
::FLD_VERSION
] ) // wrong format
2289 ||
$wrapped[self
::FLD_VERSION
] !== self
::VERSION
// wrong version
2291 return [ false, null, null, null ];
2294 if ( $wrapped[self
::FLD_TTL
] > 0 ) {
2295 // Get the approximate time left on the key
2296 $age = $now - $wrapped[self
::FLD_TIME
];
2297 $curTTL = max( $wrapped[self
::FLD_TTL
] - $age, 0.0 );
2299 // Key had no TTL, so the time left is unbounded
2303 if ( $wrapped[self
::FLD_TIME
] < $this->epoch
) {
2304 // Values this old are ignored
2305 return [ false, null, null, null ];
2308 return [ $wrapped[self
::FLD_VALUE
], $curTTL, $wrapped[self
::FLD_TIME
], null ];
2312 * @param array $keys
2313 * @param string $prefix
2316 protected static function prefixCacheKeys( array $keys, $prefix ) {
2318 foreach ( $keys as $key ) {
2319 $res[] = $prefix . $key;
2326 * @param string $key String of the format <scope>:<class>[:<class or variable>]...
2327 * @return string A collection name to describe this class of key
2329 protected function determineKeyClassForStats( $key ) {
2330 $parts = explode( ':', $key );
2332 return $parts[1] ??
$parts[0]; // sanity
2336 * @param string|array|bool $value Possible string of the form "PURGED:<timestamp>:<holdoff>"
2337 * @return array|bool Array containing a UNIX timestamp (float) and holdoff period (integer),
2338 * or false if value isn't a valid purge value
2340 protected function parsePurgeValue( $value ) {
2341 if ( !is_string( $value ) ) {
2345 $segments = explode( ':', $value, 3 );
2346 if ( !isset( $segments[0] ) ||
!isset( $segments[1] )
2347 ||
"{$segments[0]}:" !== self
::PURGE_VAL_PREFIX
2352 if ( !isset( $segments[2] ) ) {
2353 // Back-compat with old purge values without holdoff
2354 $segments[2] = self
::HOLDOFF_TTL
;
2357 if ( $segments[1] < $this->epoch
) {
2358 // Values this old are ignored
2363 self
::FLD_TIME
=> (float)$segments[1],
2364 self
::FLD_HOLDOFF
=> (int)$segments[2],
2369 * @param float $timestamp
2370 * @param int $holdoff In seconds
2371 * @return string Wrapped purge value
2373 protected function makePurgeValue( $timestamp, $holdoff ) {
2374 return self
::PURGE_VAL_PREFIX
. (float)$timestamp . ':' . (int)$holdoff;
2378 * @param string $group
2379 * @return MapCacheLRU
2381 protected function getProcessCache( $group ) {
2382 if ( !isset( $this->processCaches
[$group] ) ) {
2383 list( , $n ) = explode( ':', $group );
2384 $this->processCaches
[$group] = new MapCacheLRU( (int)$n );
2387 return $this->processCaches
[$group];
2391 * @param array $keys
2392 * @param array $opts
2394 * @return array List of keys
2396 private function getNonProcessCachedKeys( array $keys, array $opts, $pcTTL ) {
2398 if ( isset( $opts['pcTTL'] ) && $opts['pcTTL'] > 0 && $this->callbackDepth
== 0 ) {
2399 $pcGroup = $opts['pcGroup'] ?? self
::PC_PRIMARY
;
2400 $procCache = $this->getProcessCache( $pcGroup );
2401 foreach ( $keys as $key ) {
2402 if ( $procCache->has( $key, $pcTTL ) ) {
2403 $keysFound[] = $key;
2408 return array_diff( $keys, $keysFound );
2412 * @param array $keys
2413 * @param array $checkKeys
2414 * @return array Map of (cache key => mixed)
2416 private function getRawKeysForWarmup( array $keys, array $checkKeys ) {
2422 // Get all the value keys to fetch...
2423 foreach ( $keys as $key ) {
2424 $keysWarmUp[] = self
::VALUE_KEY_PREFIX
. $key;
2426 // Get all the check keys to fetch...
2427 foreach ( $checkKeys as $i => $checkKeyOrKeys ) {
2428 if ( is_int( $i ) ) {
2429 // Single check key that applies to all value keys
2430 $keysWarmUp[] = self
::TIME_KEY_PREFIX
. $checkKeyOrKeys;
2432 // List of check keys that apply to value key $i
2433 $keysWarmUp = array_merge(
2435 self
::prefixCacheKeys( $checkKeyOrKeys, self
::TIME_KEY_PREFIX
)
2440 $warmupCache = $this->cache
->getMulti( $keysWarmUp );
2441 $warmupCache +
= array_fill_keys( $keysWarmUp, false );
2443 return $warmupCache;
2447 * @return float UNIX timestamp
2448 * @codeCoverageIgnore
2450 protected function getCurrentTime() {
2451 if ( $this->wallClockOverride
) {
2452 return $this->wallClockOverride
;
2455 $clockTime = (float)time(); // call this first
2456 // microtime() uses an initial gettimeofday() call added to usage clocks.
2457 // This can severely drift from time() and the microtime() value of other threads
2458 // due to undercounting of the amount of time elapsed. Instead of seeing the current
2459 // time as being in the past, use the value of time(). This avoids setting cache values
2460 // that will immediately be seen as expired and possibly cause stampedes.
2461 return max( microtime( true ), $clockTime );
2465 * @param float|null &$time Mock UNIX timestamp for testing
2466 * @codeCoverageIgnore
2468 public function setMockTime( &$time ) {
2469 $this->wallClockOverride
=& $time;
2470 $this->cache
->setMockTime( $time );