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Diffstat (limited to 'www/wiki/includes/libs/objectcache/WANObjectCache.php')
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diff --git a/www/wiki/includes/libs/objectcache/WANObjectCache.php b/www/wiki/includes/libs/objectcache/WANObjectCache.php new file mode 100644 index 00000000..658b225b --- /dev/null +++ b/www/wiki/includes/libs/objectcache/WANObjectCache.php @@ -0,0 +1,2188 @@ +<?php +/** + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + * http://www.gnu.org/copyleft/gpl.html + * + * @file + * @ingroup Cache + */ + +use Liuggio\StatsdClient\Factory\StatsdDataFactoryInterface; +use Psr\Log\LoggerAwareInterface; +use Psr\Log\LoggerInterface; +use Psr\Log\NullLogger; + +/** + * Multi-datacenter aware caching interface + * + * All operations go to the local datacenter cache, except for delete(), + * touchCheckKey(), and resetCheckKey(), which broadcast to all datacenters. + * + * This class is intended for caching data from primary stores. + * If the get() method does not return a value, then the caller + * should query the new value and backfill the cache using set(). + * The preferred way to do this logic is through getWithSetCallback(). + * When querying the store on cache miss, the closest DB replica + * should be used. Try to avoid heavyweight DB master or quorum reads. + * When the source data changes, a purge method should be called. + * Since purges are expensive, they should be avoided. One can do so if: + * - a) The object cached is immutable; or + * - b) Validity is checked against the source after get(); or + * - c) Using a modest TTL is reasonably correct and performant + * + * The simplest purge method is delete(). + * + * There are three supported ways to handle broadcasted operations: + * - a) Configure the 'purge' EventRelayer to point to a valid PubSub endpoint + * that has subscribed listeners on the cache servers applying the cache updates. + * - b) Ommit the 'purge' EventRelayer parameter and set up mcrouter as the underlying cache + * backend, using a memcached BagOStuff class for the 'cache' parameter. The 'region' + * and 'cluster' parameters must be provided and 'mcrouterAware' must be set to 'true'. + * Configure mcrouter as follows: + * - 1) Use Route Prefixing based on region (datacenter) and cache cluster. + * See https://github.com/facebook/mcrouter/wiki/Routing-Prefix and + * https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup + * - 2) To increase the consistency of delete() and touchCheckKey() during cache + * server membership changes, you can use the OperationSelectorRoute to + * configure 'set' and 'delete' operations to go to all servers in the cache + * cluster, instead of just one server determined by hashing. + * See https://github.com/facebook/mcrouter/wiki/List-of-Route-Handles + * - c) Ommit the 'purge' EventRelayer parameter and set up dynomite as cache middleware + * between the web servers and either memcached or redis. This will also broadcast all + * key setting operations, not just purges, which can be useful for cache warming. + * Writes are eventually consistent via the Dynamo replication model. + * See https://github.com/Netflix/dynomite + * + * Broadcasted operations like delete() and touchCheckKey() are done asynchronously + * in all datacenters this way, though the local one should likely be near immediate. + * + * This means that callers in all datacenters may see older values for however many + * milliseconds that the purge took to reach that datacenter. As with any cache, this + * should not be relied on for cases where reads are used to determine writes to source + * (e.g. non-cache) data stores, except when reading immutable data. + * + * All values are wrapped in metadata arrays. Keys use a "WANCache:" prefix + * to avoid collisions with keys that are not wrapped as metadata arrays. The + * prefixes are as follows: + * - a) "WANCache:v" : used for regular value keys + * - b) "WANCache:i" : used for temporarily storing values of tombstoned keys + * - c) "WANCache:t" : used for storing timestamp "check" keys + * - d) "WANCache:m" : used for temporary mutex keys to avoid cache stampedes + * + * @ingroup Cache + * @since 1.26 + */ +class WANObjectCache implements IExpiringStore, LoggerAwareInterface { + /** @var BagOStuff The local datacenter cache */ + protected $cache; + /** @var HashBagOStuff[] Map of group PHP instance caches */ + protected $processCaches = []; + /** @var string Purge channel name */ + protected $purgeChannel; + /** @var EventRelayer Bus that handles purge broadcasts */ + protected $purgeRelayer; + /** @bar bool Whether to use mcrouter key prefixing for routing */ + protected $mcrouterAware; + /** @var string Physical region for mcrouter use */ + protected $region; + /** @var string Cache cluster name for mcrouter use */ + protected $cluster; + /** @var LoggerInterface */ + protected $logger; + /** @var StatsdDataFactoryInterface */ + protected $stats; + /** @var bool Whether to use "interim" caching while keys are tombstoned */ + protected $useInterimHoldOffCaching = true; + /** @var callable|null Function that takes a WAN cache callback and runs it later */ + protected $asyncHandler; + + /** @var int ERR_* constant for the "last error" registry */ + protected $lastRelayError = self::ERR_NONE; + + /** @var int Callback stack depth for getWithSetCallback() */ + private $callbackDepth = 0; + /** @var mixed[] Temporary warm-up cache */ + private $warmupCache = []; + /** @var int Key fetched */ + private $warmupKeyMisses = 0; + + /** @var float|null */ + private $wallClockOverride; + + /** Max time expected to pass between delete() and DB commit finishing */ + const MAX_COMMIT_DELAY = 3; + /** Max replication+snapshot lag before applying TTL_LAGGED or disallowing set() */ + const MAX_READ_LAG = 7; + /** Seconds to tombstone keys on delete() */ + const HOLDOFF_TTL = 11; // MAX_COMMIT_DELAY + MAX_READ_LAG + 1 + + /** Seconds to keep dependency purge keys around */ + const CHECK_KEY_TTL = self::TTL_YEAR; + /** Seconds to keep interim value keys for tombstoned keys around */ + const INTERIM_KEY_TTL = 1; + + /** Seconds to keep lock keys around */ + const LOCK_TTL = 10; + /** Default remaining TTL at which to consider pre-emptive regeneration */ + const LOW_TTL = 30; + + /** Never consider performing "popularity" refreshes until a key reaches this age */ + const AGE_NEW = 60; + /** The time length of the "popularity" refresh window for hot keys */ + const HOT_TTR = 900; + /** Hits/second for a refresh to be expected within the "popularity" window */ + const HIT_RATE_HIGH = 1; + /** Seconds to ramp up to the "popularity" refresh chance after a key is no longer new */ + const RAMPUP_TTL = 30; + + /** Idiom for getWithSetCallback() callbacks to avoid calling set() */ + const TTL_UNCACHEABLE = -1; + /** Idiom for getWithSetCallback() callbacks to 'lockTSE' logic */ + const TSE_NONE = -1; + /** Max TTL to store keys when a data sourced is lagged */ + const TTL_LAGGED = 30; + /** Idiom for delete() for "no hold-off" */ + const HOLDOFF_NONE = 0; + /** Idiom for set()/getWithSetCallback() for "do not augment the storage medium TTL" */ + const STALE_TTL_NONE = 0; + /** Idiom for set()/getWithSetCallback() for "no post-expired grace period" */ + const GRACE_TTL_NONE = 0; + + /** Idiom for getWithSetCallback() for "no minimum required as-of timestamp" */ + const MIN_TIMESTAMP_NONE = 0.0; + + /** Tiny negative float to use when CTL comes up >= 0 due to clock skew */ + const TINY_NEGATIVE = -0.000001; + + /** Cache format version number */ + const VERSION = 1; + + const FLD_VERSION = 0; // key to cache version number + const FLD_VALUE = 1; // key to the cached value + const FLD_TTL = 2; // key to the original TTL + const FLD_TIME = 3; // key to the cache time + const FLD_FLAGS = 4; // key to the flags bitfield + const FLD_HOLDOFF = 5; // key to any hold-off TTL + + /** @var int Treat this value as expired-on-arrival */ + const FLG_STALE = 1; + + const ERR_NONE = 0; // no error + const ERR_NO_RESPONSE = 1; // no response + const ERR_UNREACHABLE = 2; // can't connect + const ERR_UNEXPECTED = 3; // response gave some error + const ERR_RELAY = 4; // relay broadcast failed + + const VALUE_KEY_PREFIX = 'WANCache:v:'; + const INTERIM_KEY_PREFIX = 'WANCache:i:'; + const TIME_KEY_PREFIX = 'WANCache:t:'; + const MUTEX_KEY_PREFIX = 'WANCache:m:'; + + const PURGE_VAL_PREFIX = 'PURGED:'; + + const VFLD_DATA = 'WOC:d'; // key to the value of versioned data + const VFLD_VERSION = 'WOC:v'; // key to the version of the value present + + const PC_PRIMARY = 'primary:1000'; // process cache name and max key count + + const DEFAULT_PURGE_CHANNEL = 'wancache-purge'; + + /** + * @param array $params + * - cache : BagOStuff object for a persistent cache + * - channels : Map of (action => channel string). Actions include "purge". + * - relayers : Map of (action => EventRelayer object). Actions include "purge". + * - logger : LoggerInterface object + * - stats : LoggerInterface object + * - asyncHandler : A function that takes a callback and runs it later. If supplied, + * whenever a preemptive refresh would be triggered in getWithSetCallback(), the + * current cache value is still used instead. However, the async-handler function + * receives a WAN cache callback that, when run, will execute the value generation + * callback supplied by the getWithSetCallback() caller. The result will be saved + * as normal. The handler is expected to call the WAN cache callback at an opportune + * time (e.g. HTTP post-send), though generally within a few 100ms. [optional] + * - region: the current physical region. This is required when using mcrouter as the + * backing store proxy. [optional] + * - cluster: name of the cache cluster used by this WAN cache. The name must be the + * same in all datacenters; the ("region","cluster") tuple is what distinguishes + * the counterpart cache clusters among all the datacenter. The contents of + * https://github.com/facebook/mcrouter/wiki/Config-Files give background on this. + * This is required when using mcrouter as the backing store proxy. [optional] + * - mcrouterAware: set as true if mcrouter is the backing store proxy and mcrouter + * is configured to interpret /<region>/<cluster>/ key prefixes as routes. This + * requires that "region" and "cluster" are both set above. [optional] + */ + public function __construct( array $params ) { + $this->cache = $params['cache']; + $this->purgeChannel = isset( $params['channels']['purge'] ) + ? $params['channels']['purge'] + : self::DEFAULT_PURGE_CHANNEL; + $this->purgeRelayer = isset( $params['relayers']['purge'] ) + ? $params['relayers']['purge'] + : new EventRelayerNull( [] ); + $this->region = isset( $params['region'] ) ? $params['region'] : 'main'; + $this->cluster = isset( $params['cluster'] ) ? $params['cluster'] : 'wan-main'; + $this->mcrouterAware = !empty( $params['mcrouterAware'] ); + + $this->setLogger( isset( $params['logger'] ) ? $params['logger'] : new NullLogger() ); + $this->stats = isset( $params['stats'] ) ? $params['stats'] : new NullStatsdDataFactory(); + $this->asyncHandler = isset( $params['asyncHandler'] ) ? $params['asyncHandler'] : null; + } + + /** + * @param LoggerInterface $logger + */ + public function setLogger( LoggerInterface $logger ) { + $this->logger = $logger; + } + + /** + * Get an instance that wraps EmptyBagOStuff + * + * @return WANObjectCache + */ + public static function newEmpty() { + return new static( [ + 'cache' => new EmptyBagOStuff() + ] ); + } + + /** + * Fetch the value of a key from cache + * + * If supplied, $curTTL is set to the remaining TTL (current time left): + * - a) INF; if $key exists, has no TTL, and is not expired by $checkKeys + * - b) float (>=0); if $key exists, has a TTL, and is not expired by $checkKeys + * - c) float (<0); if $key is tombstoned, stale, or existing but expired by $checkKeys + * - d) null; if $key does not exist and is not tombstoned + * + * If a key is tombstoned, $curTTL will reflect the time since delete(). + * + * The timestamp of $key will be checked against the last-purge timestamp + * of each of $checkKeys. Those $checkKeys not in cache will have the last-purge + * initialized to the current timestamp. If any of $checkKeys have a timestamp + * greater than that of $key, then $curTTL will reflect how long ago $key + * became invalid. Callers can use $curTTL to know when the value is stale. + * The $checkKeys parameter allow mass invalidations by updating a single key: + * - a) Each "check" key represents "last purged" of some source data + * - b) Callers pass in relevant "check" keys as $checkKeys in get() + * - c) When the source data that "check" keys represent changes, + * the touchCheckKey() method is called on them + * + * Source data entities might exists in a DB that uses snapshot isolation + * (e.g. the default REPEATABLE-READ in innoDB). Even for mutable data, that + * isolation can largely be maintained by doing the following: + * - a) Calling delete() on entity change *and* creation, before DB commit + * - b) Keeping transaction duration shorter than the delete() hold-off TTL + * - c) Disabling interim key caching via useInterimHoldOffCaching() before get() calls + * + * However, pre-snapshot values might still be seen if an update was made + * in a remote datacenter but the purge from delete() didn't relay yet. + * + * Consider using getWithSetCallback() instead of get() and set() cycles. + * That method has cache slam avoiding features for hot/expensive keys. + * + * @param string $key Cache key made from makeKey() or makeGlobalKey() + * @param mixed &$curTTL Approximate TTL left on the key if present/tombstoned [returned] + * @param array $checkKeys List of "check" keys + * @param float &$asOf UNIX timestamp of cached value; null on failure [returned] + * @return mixed Value of cache key or false on failure + */ + final public function get( $key, &$curTTL = null, array $checkKeys = [], &$asOf = null ) { + $curTTLs = []; + $asOfs = []; + $values = $this->getMulti( [ $key ], $curTTLs, $checkKeys, $asOfs ); + $curTTL = isset( $curTTLs[$key] ) ? $curTTLs[$key] : null; + $asOf = isset( $asOfs[$key] ) ? $asOfs[$key] : null; + + return isset( $values[$key] ) ? $values[$key] : false; + } + + /** + * Fetch the value of several keys from cache + * + * @see WANObjectCache::get() + * + * @param array $keys List of cache keys made from makeKey() or makeGlobalKey() + * @param array &$curTTLs Map of (key => approximate TTL left) for existing keys [returned] + * @param array $checkKeys List of check keys to apply to all $keys. May also apply "check" + * keys to specific cache keys only by using cache keys as keys in the $checkKeys array. + * @param float[] &$asOfs Map of (key => UNIX timestamp of cached value; null on failure) + * @return array Map of (key => value) for keys that exist and are not tombstoned + */ + final public function getMulti( + array $keys, &$curTTLs = [], array $checkKeys = [], array &$asOfs = [] + ) { + $result = []; + $curTTLs = []; + $asOfs = []; + + $vPrefixLen = strlen( self::VALUE_KEY_PREFIX ); + $valueKeys = self::prefixCacheKeys( $keys, self::VALUE_KEY_PREFIX ); + + $checkKeysForAll = []; + $checkKeysByKey = []; + $checkKeysFlat = []; + foreach ( $checkKeys as $i => $checkKeyGroup ) { + $prefixed = self::prefixCacheKeys( (array)$checkKeyGroup, self::TIME_KEY_PREFIX ); + $checkKeysFlat = array_merge( $checkKeysFlat, $prefixed ); + // Is this check keys for a specific cache key, or for all keys being fetched? + if ( is_int( $i ) ) { + $checkKeysForAll = array_merge( $checkKeysForAll, $prefixed ); + } else { + $checkKeysByKey[$i] = isset( $checkKeysByKey[$i] ) + ? array_merge( $checkKeysByKey[$i], $prefixed ) + : $prefixed; + } + } + + // Fetch all of the raw values + $keysGet = array_merge( $valueKeys, $checkKeysFlat ); + if ( $this->warmupCache ) { + $wrappedValues = array_intersect_key( $this->warmupCache, array_flip( $keysGet ) ); + $keysGet = array_diff( $keysGet, array_keys( $wrappedValues ) ); // keys left to fetch + $this->warmupKeyMisses += count( $keysGet ); + } else { + $wrappedValues = []; + } + if ( $keysGet ) { + $wrappedValues += $this->cache->getMulti( $keysGet ); + } + // Time used to compare/init "check" keys (derived after getMulti() to be pessimistic) + $now = $this->getCurrentTime(); + + // Collect timestamps from all "check" keys + $purgeValuesForAll = $this->processCheckKeys( $checkKeysForAll, $wrappedValues, $now ); + $purgeValuesByKey = []; + foreach ( $checkKeysByKey as $cacheKey => $checks ) { + $purgeValuesByKey[$cacheKey] = + $this->processCheckKeys( $checks, $wrappedValues, $now ); + } + + // Get the main cache value for each key and validate them + foreach ( $valueKeys as $vKey ) { + if ( !isset( $wrappedValues[$vKey] ) ) { + continue; // not found + } + + $key = substr( $vKey, $vPrefixLen ); // unprefix + + list( $value, $curTTL ) = $this->unwrap( $wrappedValues[$vKey], $now ); + if ( $value !== false ) { + $result[$key] = $value; + + // Force dependant keys to be invalid for a while after purging + // to reduce race conditions involving stale data getting cached + $purgeValues = $purgeValuesForAll; + if ( isset( $purgeValuesByKey[$key] ) ) { + $purgeValues = array_merge( $purgeValues, $purgeValuesByKey[$key] ); + } + foreach ( $purgeValues as $purge ) { + $safeTimestamp = $purge[self::FLD_TIME] + $purge[self::FLD_HOLDOFF]; + if ( $safeTimestamp >= $wrappedValues[$vKey][self::FLD_TIME] ) { + // How long ago this value was expired by *this* check key + $ago = min( $purge[self::FLD_TIME] - $now, self::TINY_NEGATIVE ); + // How long ago this value was expired by *any* known check key + $curTTL = min( $curTTL, $ago ); + } + } + } + $curTTLs[$key] = $curTTL; + $asOfs[$key] = ( $value !== false ) ? $wrappedValues[$vKey][self::FLD_TIME] : null; + } + + return $result; + } + + /** + * @since 1.27 + * @param array $timeKeys List of prefixed time check keys + * @param array $wrappedValues + * @param float $now + * @return array List of purge value arrays + */ + private function processCheckKeys( array $timeKeys, array $wrappedValues, $now ) { + $purgeValues = []; + foreach ( $timeKeys as $timeKey ) { + $purge = isset( $wrappedValues[$timeKey] ) + ? $this->parsePurgeValue( $wrappedValues[$timeKey] ) + : false; + if ( $purge === false ) { + // Key is not set or invalid; regenerate + $newVal = $this->makePurgeValue( $now, self::HOLDOFF_TTL ); + $this->cache->add( $timeKey, $newVal, self::CHECK_KEY_TTL ); + $purge = $this->parsePurgeValue( $newVal ); + } + $purgeValues[] = $purge; + } + return $purgeValues; + } + + /** + * Set the value of a key in cache + * + * Simply calling this method when source data changes is not valid because + * the changes do not replicate to the other WAN sites. In that case, delete() + * should be used instead. This method is intended for use on cache misses. + * + * If the data was read from a snapshot-isolated transactions (e.g. the default + * REPEATABLE-READ in innoDB), use 'since' to avoid the following race condition: + * - a) T1 starts + * - b) T2 updates a row, calls delete(), and commits + * - c) The HOLDOFF_TTL passes, expiring the delete() tombstone + * - d) T1 reads the row and calls set() due to a cache miss + * - e) Stale value is stuck in cache + * + * Setting 'lag' and 'since' help avoids keys getting stuck in stale states. + * + * Be aware that this does not update the process cache for getWithSetCallback() + * callers. Keys accessed via that method are not generally meant to also be set + * using this primitive method. + * + * Do not use this method on versioned keys accessed via getWithSetCallback(). + * + * Example usage: + * @code + * $dbr = wfGetDB( DB_REPLICA ); + * $setOpts = Database::getCacheSetOptions( $dbr ); + * // Fetch the row from the DB + * $row = $dbr->selectRow( ... ); + * $key = $cache->makeKey( 'building', $buildingId ); + * $cache->set( $key, $row, $cache::TTL_DAY, $setOpts ); + * @endcode + * + * @param string $key Cache key + * @param mixed $value + * @param int $ttl Seconds to live. Special values are: + * - WANObjectCache::TTL_INDEFINITE: Cache forever + * @param array $opts Options map: + * - lag : Seconds of replica DB lag. Typically, this is either the replica DB lag + * before the data was read or, if applicable, the replica DB lag before + * the snapshot-isolated transaction the data was read from started. + * Use false to indicate that replication is not running. + * Default: 0 seconds + * - since : UNIX timestamp of the data in $value. Typically, this is either + * the current time the data was read or (if applicable) the time when + * the snapshot-isolated transaction the data was read from started. + * Default: 0 seconds + * - pending : Whether this data is possibly from an uncommitted write transaction. + * Generally, other threads should not see values from the future and + * they certainly should not see ones that ended up getting rolled back. + * Default: false + * - lockTSE : if excessive replication/snapshot lag is detected, then store the value + * with this TTL and flag it as stale. This is only useful if the reads for this key + * use getWithSetCallback() with "lockTSE" set. Note that if "staleTTL" is set + * then it will still add on to this TTL in the excessive lag scenario. + * Default: WANObjectCache::TSE_NONE + * - staleTTL : Seconds to keep the key around if it is stale. The get()/getMulti() + * methods return such stale values with a $curTTL of 0, and getWithSetCallback() + * will call the regeneration callback in such cases, passing in the old value + * and its as-of time to the callback. This is useful if adaptiveTTL() is used + * on the old value's as-of time when it is verified as still being correct. + * Default: WANObjectCache::STALE_TTL_NONE. + * @note Options added in 1.28: staleTTL + * @return bool Success + */ + final public function set( $key, $value, $ttl = 0, array $opts = [] ) { + $now = $this->getCurrentTime(); + $lockTSE = isset( $opts['lockTSE'] ) ? $opts['lockTSE'] : self::TSE_NONE; + $staleTTL = isset( $opts['staleTTL'] ) ? $opts['staleTTL'] : self::STALE_TTL_NONE; + $age = isset( $opts['since'] ) ? max( 0, $now - $opts['since'] ) : 0; + $lag = isset( $opts['lag'] ) ? $opts['lag'] : 0; + + // Do not cache potentially uncommitted data as it might get rolled back + if ( !empty( $opts['pending'] ) ) { + $this->logger->info( 'Rejected set() for {cachekey} due to pending writes.', + [ 'cachekey' => $key ] ); + + return true; // no-op the write for being unsafe + } + + $wrapExtra = []; // additional wrapped value fields + // Check if there's a risk of writing stale data after the purge tombstone expired + if ( $lag === false || ( $lag + $age ) > self::MAX_READ_LAG ) { + // Case A: read lag with "lockTSE"; save but record value as stale + if ( $lockTSE >= 0 ) { + $ttl = max( 1, (int)$lockTSE ); // set() expects seconds + $wrapExtra[self::FLD_FLAGS] = self::FLG_STALE; // mark as stale + // Case B: any long-running transaction; ignore this set() + } elseif ( $age > self::MAX_READ_LAG ) { + $this->logger->info( 'Rejected set() for {cachekey} due to snapshot lag.', + [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] ); + + return true; // no-op the write for being unsafe + // Case C: high replication lag; lower TTL instead of ignoring all set()s + } elseif ( $lag === false || $lag > self::MAX_READ_LAG ) { + $ttl = $ttl ? min( $ttl, self::TTL_LAGGED ) : self::TTL_LAGGED; + $this->logger->warning( 'Lowered set() TTL for {cachekey} due to replication lag.', + [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] ); + // Case D: medium length request with medium replication lag; ignore this set() + } else { + $this->logger->info( 'Rejected set() for {cachekey} due to high read lag.', + [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ] ); + + return true; // no-op the write for being unsafe + } + } + + // Wrap that value with time/TTL/version metadata + $wrapped = $this->wrap( $value, $ttl, $now ) + $wrapExtra; + + $func = function ( $cache, $key, $cWrapped ) use ( $wrapped ) { + return ( is_string( $cWrapped ) ) + ? false // key is tombstoned; do nothing + : $wrapped; + }; + + return $this->cache->merge( self::VALUE_KEY_PREFIX . $key, $func, $ttl + $staleTTL, 1 ); + } + + /** + * Purge a key from all datacenters + * + * This should only be called when the underlying data (being cached) + * changes in a significant way. This deletes the key and starts a hold-off + * period where the key cannot be written to for a few seconds (HOLDOFF_TTL). + * This is done to avoid the following race condition: + * - a) Some DB data changes and delete() is called on a corresponding key + * - b) A request refills the key with a stale value from a lagged DB + * - c) The stale value is stuck there until the key is expired/evicted + * + * This is implemented by storing a special "tombstone" value at the cache + * key that this class recognizes; get() calls will return false for the key + * and any set() calls will refuse to replace tombstone values at the key. + * For this to always avoid stale value writes, the following must hold: + * - a) Replication lag is bounded to being less than HOLDOFF_TTL; or + * - b) If lag is higher, the DB will have gone into read-only mode already + * + * Note that set() can also be lag-aware and lower the TTL if it's high. + * + * Be aware that this does not clear the process cache. Even if it did, callbacks + * used by getWithSetCallback() might still return stale data in the case of either + * uncommitted or not-yet-replicated changes (callback generally use replica DBs). + * + * When using potentially long-running ACID transactions, a good pattern is + * to use a pre-commit hook to issue the delete. This means that immediately + * after commit, callers will see the tombstone in cache upon purge relay. + * It also avoids the following race condition: + * - a) T1 begins, changes a row, and calls delete() + * - b) The HOLDOFF_TTL passes, expiring the delete() tombstone + * - c) T2 starts, reads the row and calls set() due to a cache miss + * - d) T1 finally commits + * - e) Stale value is stuck in cache + * + * Example usage: + * @code + * $dbw->startAtomic( __METHOD__ ); // start of request + * ... <execute some stuff> ... + * // Update the row in the DB + * $dbw->update( ... ); + * $key = $cache->makeKey( 'homes', $homeId ); + * // Purge the corresponding cache entry just before committing + * $dbw->onTransactionPreCommitOrIdle( function() use ( $cache, $key ) { + * $cache->delete( $key ); + * } ); + * ... <execute some stuff> ... + * $dbw->endAtomic( __METHOD__ ); // end of request + * @endcode + * + * The $ttl parameter can be used when purging values that have not actually changed + * recently. For example, a cleanup script to purge cache entries does not really need + * a hold-off period, so it can use HOLDOFF_NONE. Likewise for user-requested purge. + * Note that $ttl limits the effective range of 'lockTSE' for getWithSetCallback(). + * + * If called twice on the same key, then the last hold-off TTL takes precedence. For + * idempotence, the $ttl should not vary for different delete() calls on the same key. + * + * @param string $key Cache key + * @param int $ttl Tombstone TTL; Default: WANObjectCache::HOLDOFF_TTL + * @return bool True if the item was purged or not found, false on failure + */ + final public function delete( $key, $ttl = self::HOLDOFF_TTL ) { + $key = self::VALUE_KEY_PREFIX . $key; + + if ( $ttl <= 0 ) { + // Publish the purge to all datacenters + $ok = $this->relayDelete( $key ); + } else { + // Publish the purge to all datacenters + $ok = $this->relayPurge( $key, $ttl, self::HOLDOFF_NONE ); + } + + return $ok; + } + + /** + * Fetch the value of a timestamp "check" key + * + * The key will be *initialized* to the current time if not set, + * so only call this method if this behavior is actually desired + * + * The timestamp can be used to check whether a cached value is valid. + * Callers should not assume that this returns the same timestamp in + * all datacenters due to relay delays. + * + * The level of staleness can roughly be estimated from this key, but + * if the key was evicted from cache, such calculations may show the + * time since expiry as ~0 seconds. + * + * Note that "check" keys won't collide with other regular keys. + * + * @param string $key + * @return float UNIX timestamp + */ + final public function getCheckKeyTime( $key ) { + return $this->getMultiCheckKeyTime( [ $key ] )[$key]; + } + + /** + * Fetch the values of each timestamp "check" key + * + * This works like getCheckKeyTime() except it takes a list of keys + * and returns a map of timestamps instead of just that of one key + * + * This might be useful if both: + * - a) a class of entities each depend on hundreds of other entities + * - b) these other entities are depended upon by millions of entities + * + * The later entities can each use a "check" key to invalidate their dependee entities. + * However, it is expensive for the former entities to verify against all of the relevant + * "check" keys during each getWithSetCallback() call. A less expensive approach is to do + * these verifications only after a "time-till-verify" (TTV) has passed. This is a middle + * ground between using blind TTLs and using constant verification. The adaptiveTTL() method + * can be used to dynamically adjust the TTV. Also, the initial TTV can make use of the + * last-modified times of the dependant entities (either from the DB or the "check" keys). + * + * Example usage: + * @code + * $value = $cache->getWithSetCallback( + * $cache->makeGlobalKey( 'wikibase-item', $id ), + * self::INITIAL_TTV, // initial time-till-verify + * function ( $oldValue, &$ttv, &$setOpts, $oldAsOf ) use ( $checkKeys, $cache ) { + * $now = microtime( true ); + * // Use $oldValue if it passes max ultimate age and "check" key comparisons + * if ( $oldValue && + * $oldAsOf > max( $cache->getMultiCheckKeyTime( $checkKeys ) ) && + * ( $now - $oldValue['ctime'] ) <= self::MAX_CACHE_AGE + * ) { + * // Increase time-till-verify by 50% of last time to reduce overhead + * $ttv = $cache->adaptiveTTL( $oldAsOf, self::MAX_TTV, self::MIN_TTV, 1.5 ); + * // Unlike $oldAsOf, "ctime" is the ultimate age of the cached data + * return $oldValue; + * } + * + * $mtimes = []; // dependency last-modified times; passed by reference + * $value = [ 'data' => $this->fetchEntityData( $mtimes ), 'ctime' => $now ]; + * // Guess time-till-change among the dependencies, e.g. 1/(total change rate) + * $ttc = 1 / array_sum( array_map( + * function ( $mtime ) use ( $now ) { + * return 1 / ( $mtime ? ( $now - $mtime ) : 900 ); + * }, + * $mtimes + * ) ); + * // The time-to-verify should not be overly pessimistic nor optimistic + * $ttv = min( max( $ttc, self::MIN_TTV ), self::MAX_TTV ); + * + * return $value; + * }, + * [ 'staleTTL' => $cache::TTL_DAY ] // keep around to verify and re-save + * ); + * @endcode + * + * @see WANObjectCache::getCheckKeyTime() + * @see WANObjectCache::getWithSetCallback() + * + * @param array $keys + * @return float[] Map of (key => UNIX timestamp) + * @since 1.31 + */ + final public function getMultiCheckKeyTime( array $keys ) { + $rawKeys = []; + foreach ( $keys as $key ) { + $rawKeys[$key] = self::TIME_KEY_PREFIX . $key; + } + + $rawValues = $this->cache->getMulti( $rawKeys ); + $rawValues += array_fill_keys( $rawKeys, false ); + + $times = []; + foreach ( $rawKeys as $key => $rawKey ) { + $purge = $this->parsePurgeValue( $rawValues[$rawKey] ); + if ( $purge !== false ) { + $time = $purge[self::FLD_TIME]; + } else { + // Casting assures identical floats for the next getCheckKeyTime() calls + $now = (string)$this->getCurrentTime(); + $this->cache->add( + $rawKey, + $this->makePurgeValue( $now, self::HOLDOFF_TTL ), + self::CHECK_KEY_TTL + ); + $time = (float)$now; + } + + $times[$key] = $time; + } + + return $times; + } + + /** + * Purge a "check" key from all datacenters, invalidating keys that use it + * + * This should only be called when the underlying data (being cached) + * changes in a significant way, and it is impractical to call delete() + * on all keys that should be changed. When get() is called on those + * keys, the relevant "check" keys must be supplied for this to work. + * + * The "check" key essentially represents a last-modified time of an entity. + * When the key is touched, the timestamp will be updated to the current time. + * Keys using the "check" key via get(), getMulti(), or getWithSetCallback() will + * be invalidated. This approach is useful if many keys depend on a single entity. + * + * The timestamp of the "check" key is treated as being HOLDOFF_TTL seconds in the + * future by get*() methods in order to avoid race conditions where keys are updated + * with stale values (e.g. from a lagged replica DB). A high TTL is set on the "check" + * key, making it possible to know the timestamp of the last change to the corresponding + * entities in most cases. This might use more cache space than resetCheckKey(). + * + * When a few important keys get a large number of hits, a high cache time is usually + * desired as well as "lockTSE" logic. The resetCheckKey() method is less appropriate + * in such cases since the "time since expiry" cannot be inferred, causing any get() + * after the reset to treat the key as being "hot", resulting in more stale value usage. + * + * Note that "check" keys won't collide with other regular keys. + * + * @see WANObjectCache::get() + * @see WANObjectCache::getWithSetCallback() + * @see WANObjectCache::resetCheckKey() + * + * @param string $key Cache key + * @param int $holdoff HOLDOFF_TTL or HOLDOFF_NONE constant + * @return bool True if the item was purged or not found, false on failure + */ + final public function touchCheckKey( $key, $holdoff = self::HOLDOFF_TTL ) { + // Publish the purge to all datacenters + return $this->relayPurge( self::TIME_KEY_PREFIX . $key, self::CHECK_KEY_TTL, $holdoff ); + } + + /** + * Delete a "check" key from all datacenters, invalidating keys that use it + * + * This is similar to touchCheckKey() in that keys using it via get(), getMulti(), + * or getWithSetCallback() will be invalidated. The differences are: + * - a) The "check" key will be deleted from all caches and lazily + * re-initialized when accessed (rather than set everywhere) + * - b) Thus, dependent keys will be known to be invalid, but not + * for how long (they are treated as "just" purged), which + * effects any lockTSE logic in getWithSetCallback() + * - c) Since "check" keys are initialized only on the server the key hashes + * to, any temporary ejection of that server will cause the value to be + * seen as purged as a new server will initialize the "check" key. + * + * The advantage here is that the "check" keys, which have high TTLs, will only + * be created when a get*() method actually uses that key. This is better when + * a large number of "check" keys are invalided in a short period of time. + * + * Note that "check" keys won't collide with other regular keys. + * + * @see WANObjectCache::get() + * @see WANObjectCache::getWithSetCallback() + * @see WANObjectCache::touchCheckKey() + * + * @param string $key Cache key + * @return bool True if the item was purged or not found, false on failure + */ + final public function resetCheckKey( $key ) { + // Publish the purge to all datacenters + return $this->relayDelete( self::TIME_KEY_PREFIX . $key ); + } + + /** + * Method to fetch/regenerate cache keys + * + * On cache miss, the key will be set to the callback result via set() + * (unless the callback returns false) and that result will be returned. + * The arguments supplied to the callback are: + * - $oldValue : current cache value or false if not present + * - &$ttl : a reference to the TTL which can be altered + * - &$setOpts : a reference to options for set() which can be altered + * - $oldAsOf : generation UNIX timestamp of $oldValue or null if not present (since 1.28) + * + * It is strongly recommended to set the 'lag' and 'since' fields to avoid race conditions + * that can cause stale values to get stuck at keys. Usually, callbacks ignore the current + * value, but it can be used to maintain "most recent X" values that come from time or + * sequence based source data, provided that the "as of" id/time is tracked. Note that + * preemptive regeneration and $checkKeys can result in a non-false current value. + * + * Usage of $checkKeys is similar to get() and getMulti(). However, rather than the caller + * having to inspect a "current time left" variable (e.g. $curTTL, $curTTLs), a cache + * regeneration will automatically be triggered using the callback. + * + * The $ttl argument and "hotTTR" option (in $opts) use time-dependant randomization + * to avoid stampedes. Keys that are slow to regenerate and either heavily used + * or subject to explicit (unpredictable) purges, may need additional mechanisms. + * The simplest way to avoid stampedes for such keys is to use 'lockTSE' (in $opts). + * If explicit purges are needed, also: + * - a) Pass $key into $checkKeys + * - b) Use touchCheckKey( $key ) instead of delete( $key ) + * + * Example usage (typical key): + * @code + * $catInfo = $cache->getWithSetCallback( + * // Key to store the cached value under + * $cache->makeKey( 'cat-attributes', $catId ), + * // Time-to-live (in seconds) + * $cache::TTL_MINUTE, + * // Function that derives the new key value + * function ( $oldValue, &$ttl, array &$setOpts ) { + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * return $dbr->selectRow( ... ); + * } + * ); + * @endcode + * + * Example usage (key that is expensive and hot): + * @code + * $catConfig = $cache->getWithSetCallback( + * // Key to store the cached value under + * $cache->makeKey( 'site-cat-config' ), + * // Time-to-live (in seconds) + * $cache::TTL_DAY, + * // Function that derives the new key value + * function ( $oldValue, &$ttl, array &$setOpts ) { + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * return CatConfig::newFromRow( $dbr->selectRow( ... ) ); + * }, + * [ + * // Calling touchCheckKey() on this key invalidates the cache + * 'checkKeys' => [ $cache->makeKey( 'site-cat-config' ) ], + * // Try to only let one datacenter thread manage cache updates at a time + * 'lockTSE' => 30, + * // Avoid querying cache servers multiple times in a web request + * 'pcTTL' => $cache::TTL_PROC_LONG + * ] + * ); + * @endcode + * + * Example usage (key with dynamic dependencies): + * @code + * $catState = $cache->getWithSetCallback( + * // Key to store the cached value under + * $cache->makeKey( 'cat-state', $cat->getId() ), + * // Time-to-live (seconds) + * $cache::TTL_HOUR, + * // Function that derives the new key value + * function ( $oldValue, &$ttl, array &$setOpts ) { + * // Determine new value from the DB + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * return CatState::newFromResults( $dbr->select( ... ) ); + * }, + * [ + * // The "check" keys that represent things the value depends on; + * // Calling touchCheckKey() on any of them invalidates the cache + * 'checkKeys' => [ + * $cache->makeKey( 'sustenance-bowls', $cat->getRoomId() ), + * $cache->makeKey( 'people-present', $cat->getHouseId() ), + * $cache->makeKey( 'cat-laws', $cat->getCityId() ), + * ] + * ] + * ); + * @endcode + * + * Example usage (hot key holding most recent 100 events): + * @code + * $lastCatActions = $cache->getWithSetCallback( + * // Key to store the cached value under + * $cache->makeKey( 'cat-last-actions', 100 ), + * // Time-to-live (in seconds) + * 10, + * // Function that derives the new key value + * function ( $oldValue, &$ttl, array &$setOpts ) { + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * // Start off with the last cached list + * $list = $oldValue ?: []; + * // Fetch the last 100 relevant rows in descending order; + * // only fetch rows newer than $list[0] to reduce scanning + * $rows = iterator_to_array( $dbr->select( ... ) ); + * // Merge them and get the new "last 100" rows + * return array_slice( array_merge( $new, $list ), 0, 100 ); + * }, + * [ + * // Try to only let one datacenter thread manage cache updates at a time + * 'lockTSE' => 30, + * // Use a magic value when no cache value is ready rather than stampeding + * 'busyValue' => 'computing' + * ] + * ); + * @endcode + * + * Example usage (key holding an LRU subkey:value map; this can avoid flooding cache with + * keys for an unlimited set of (constraint,situation) pairs, thereby avoiding elevated + * cache evictions and wasted memory): + * @code + * $catSituationTolerabilityCache = $this->cache->getWithSetCallback( + * // Group by constraint ID/hash, cat family ID/hash, or something else useful + * $this->cache->makeKey( 'cat-situation-tolerablity-checks', $groupKey ), + * WANObjectCache::TTL_DAY, // rarely used groups should fade away + * // The $scenarioKey format is $constraintId:<ID/hash of $situation> + * function ( $cacheMap ) use ( $scenarioKey, $constraintId, $situation ) { + * $lruCache = MapCacheLRU::newFromArray( $cacheMap ?: [], self::CACHE_SIZE ); + * $result = $lruCache->get( $scenarioKey ); // triggers LRU bump if present + * if ( $result === null || $this->isScenarioResultExpired( $result ) ) { + * $result = $this->checkScenarioTolerability( $constraintId, $situation ); + * $lruCache->set( $scenarioKey, $result, 3 / 8 ); + * } + * // Save the new LRU cache map and reset the map's TTL + * return $lruCache->toArray(); + * }, + * [ + * // Once map is > 1 sec old, consider refreshing + * 'ageNew' => 1, + * // Update within 5 seconds after "ageNew" given a 1hz cache check rate + * 'hotTTR' => 5, + * // Avoid querying cache servers multiple times in a request; this also means + * // that a request can only alter the value of any given constraint key once + * 'pcTTL' => WANObjectCache::TTL_PROC_LONG + * ] + * ); + * $tolerability = isset( $catSituationTolerabilityCache[$scenarioKey] ) + * ? $catSituationTolerabilityCache[$scenarioKey] + * : $this->checkScenarioTolerability( $constraintId, $situation ); + * @endcode + * + * @see WANObjectCache::get() + * @see WANObjectCache::set() + * + * @param string $key Cache key made from makeKey() or makeGlobalKey() + * @param int $ttl Seconds to live for key updates. Special values are: + * - WANObjectCache::TTL_INDEFINITE: Cache forever (subject to LRU-style evictions) + * - WANObjectCache::TTL_UNCACHEABLE: Do not cache (if the key exists, it is not deleted) + * @param callable $callback Value generation function + * @param array $opts Options map: + * - checkKeys: List of "check" keys. The key at $key will be seen as invalid when either + * touchCheckKey() or resetCheckKey() is called on any of the keys in this list. This + * is useful if thousands or millions of keys depend on the same entity. The entity can + * simply have its "check" key updated whenever the entity is modified. + * Default: []. + * - graceTTL: Consider reusing expired values instead of refreshing them if they expired + * less than this many seconds ago. The odds of a refresh becomes more likely over time, + * becoming certain once the grace period is reached. This can reduce traffic spikes + * when millions of keys are compared to the same "check" key and touchCheckKey() + * or resetCheckKey() is called on that "check" key. + * Default: WANObjectCache::GRACE_TTL_NONE. + * - lockTSE: If the key is tombstoned or expired (by checkKeys) less than this many seconds + * ago, then try to have a single thread handle cache regeneration at any given time. + * Other threads will try to use stale values if possible. If, on miss, the time since + * expiration is low, the assumption is that the key is hot and that a stampede is worth + * avoiding. Setting this above WANObjectCache::HOLDOFF_TTL makes no difference. The + * higher this is set, the higher the worst-case staleness can be. + * Use WANObjectCache::TSE_NONE to disable this logic. + * Default: WANObjectCache::TSE_NONE. + * - busyValue: If no value exists and another thread is currently regenerating it, use this + * as a fallback value (or a callback to generate such a value). This assures that cache + * stampedes cannot happen if the value falls out of cache. This can be used as insurance + * against cache regeneration becoming very slow for some reason (greater than the TTL). + * Default: null. + * - pcTTL: Process cache the value in this PHP instance for this many seconds. This avoids + * network I/O when a key is read several times. This will not cache when the callback + * returns false, however. Note that any purges will not be seen while process cached; + * since the callback should use replica DBs and they may be lagged or have snapshot + * isolation anyway, this should not typically matter. + * Default: WANObjectCache::TTL_UNCACHEABLE. + * - pcGroup: Process cache group to use instead of the primary one. If set, this must be + * of the format ALPHANUMERIC_NAME:MAX_KEY_SIZE, e.g. "mydata:10". Use this for storing + * large values, small yet numerous values, or some values with a high cost of eviction. + * It is generally preferable to use a class constant when setting this value. + * This has no effect unless pcTTL is used. + * Default: WANObjectCache::PC_PRIMARY. + * - version: Integer version number. This allows for callers to make breaking changes to + * how values are stored while maintaining compatability and correct cache purges. New + * versions are stored alongside older versions concurrently. Avoid storing class objects + * however, as this reduces compatibility (due to serialization). + * Default: null. + * - minAsOf: Reject values if they were generated before this UNIX timestamp. + * This is useful if the source of a key is suspected of having possibly changed + * recently, and the caller wants any such changes to be reflected. + * Default: WANObjectCache::MIN_TIMESTAMP_NONE. + * - hotTTR: Expected time-till-refresh (TTR) in seconds for keys that average ~1 hit per + * second (e.g. 1Hz). Keys with a hit rate higher than 1Hz will refresh sooner than this + * TTR and vise versa. Such refreshes won't happen until keys are "ageNew" seconds old. + * This uses randomization to avoid triggering cache stampedes. The TTR is useful at + * reducing the impact of missed cache purges, since the effect of a heavily referenced + * key being stale is worse than that of a rarely referenced key. Unlike simply lowering + * $ttl, seldomly used keys are largely unaffected by this option, which makes it + * possible to have a high hit rate for the "long-tail" of less-used keys. + * Default: WANObjectCache::HOT_TTR. + * - lowTTL: Consider pre-emptive updates when the current TTL (seconds) of the key is less + * than this. It becomes more likely over time, becoming certain once the key is expired. + * This helps avoid cache stampedes that might be triggered due to the key expiring. + * Default: WANObjectCache::LOW_TTL. + * - ageNew: Consider popularity refreshes only once a key reaches this age in seconds. + * Default: WANObjectCache::AGE_NEW. + * - staleTTL: Seconds to keep the key around if it is stale. This means that on cache + * miss the callback may get $oldValue/$oldAsOf values for keys that have already been + * expired for this specified time. This is useful if adaptiveTTL() is used on the old + * value's as-of time when it is verified as still being correct. + * Default: WANObjectCache::STALE_TTL_NONE + * @return mixed Value found or written to the key + * @note Options added in 1.28: version, busyValue, hotTTR, ageNew, pcGroup, minAsOf + * @note Options added in 1.31: staleTTL, graceTTL + * @note Callable type hints are not used to avoid class-autoloading + */ + final public function getWithSetCallback( $key, $ttl, $callback, array $opts = [] ) { + $pcTTL = isset( $opts['pcTTL'] ) ? $opts['pcTTL'] : self::TTL_UNCACHEABLE; + + // Try the process cache if enabled and the cache callback is not within a cache callback. + // Process cache use in nested callbacks is not lag-safe with regard to HOLDOFF_TTL since + // the in-memory value is further lagged than the shared one since it uses a blind TTL. + if ( $pcTTL >= 0 && $this->callbackDepth == 0 ) { + $group = isset( $opts['pcGroup'] ) ? $opts['pcGroup'] : self::PC_PRIMARY; + $procCache = $this->getProcessCache( $group ); + $value = $procCache->get( $key ); + } else { + $procCache = false; + $value = false; + } + + if ( $value === false ) { + // Fetch the value over the network + if ( isset( $opts['version'] ) ) { + $version = $opts['version']; + $asOf = null; + $cur = $this->doGetWithSetCallback( + $key, + $ttl, + function ( $oldValue, &$ttl, &$setOpts, $oldAsOf ) + use ( $callback, $version ) { + if ( is_array( $oldValue ) + && array_key_exists( self::VFLD_DATA, $oldValue ) + && array_key_exists( self::VFLD_VERSION, $oldValue ) + && $oldValue[self::VFLD_VERSION] === $version + ) { + $oldData = $oldValue[self::VFLD_DATA]; + } else { + // VFLD_DATA is not set if an old, unversioned, key is present + $oldData = false; + $oldAsOf = null; + } + + return [ + self::VFLD_DATA => $callback( $oldData, $ttl, $setOpts, $oldAsOf ), + self::VFLD_VERSION => $version + ]; + }, + $opts, + $asOf + ); + if ( $cur[self::VFLD_VERSION] === $version ) { + // Value created or existed before with version; use it + $value = $cur[self::VFLD_DATA]; + } else { + // Value existed before with a different version; use variant key. + // Reflect purges to $key by requiring that this key value be newer. + $value = $this->doGetWithSetCallback( + $this->makeGlobalKey( 'WANCache-key-variant', md5( $key ), $version ), + $ttl, + $callback, + // Regenerate value if not newer than $key + [ 'version' => null, 'minAsOf' => $asOf ] + $opts + ); + } + } else { + $value = $this->doGetWithSetCallback( $key, $ttl, $callback, $opts ); + } + + // Update the process cache if enabled + if ( $procCache && $value !== false ) { + $procCache->set( $key, $value, $pcTTL ); + } + } + + return $value; + } + + /** + * Do the actual I/O for getWithSetCallback() when needed + * + * @see WANObjectCache::getWithSetCallback() + * + * @param string $key + * @param int $ttl + * @param callback $callback + * @param array $opts Options map for getWithSetCallback() + * @param float &$asOf Cache generation timestamp of returned value [returned] + * @return mixed + * @note Callable type hints are not used to avoid class-autoloading + */ + protected function doGetWithSetCallback( $key, $ttl, $callback, array $opts, &$asOf = null ) { + $lowTTL = isset( $opts['lowTTL'] ) ? $opts['lowTTL'] : min( self::LOW_TTL, $ttl ); + $lockTSE = isset( $opts['lockTSE'] ) ? $opts['lockTSE'] : self::TSE_NONE; + $staleTTL = isset( $opts['staleTTL'] ) ? $opts['staleTTL'] : self::STALE_TTL_NONE; + $graceTTL = isset( $opts['graceTTL'] ) ? $opts['graceTTL'] : self::GRACE_TTL_NONE; + $checkKeys = isset( $opts['checkKeys'] ) ? $opts['checkKeys'] : []; + $busyValue = isset( $opts['busyValue'] ) ? $opts['busyValue'] : null; + $popWindow = isset( $opts['hotTTR'] ) ? $opts['hotTTR'] : self::HOT_TTR; + $ageNew = isset( $opts['ageNew'] ) ? $opts['ageNew'] : self::AGE_NEW; + $minTime = isset( $opts['minAsOf'] ) ? $opts['minAsOf'] : self::MIN_TIMESTAMP_NONE; + $versioned = isset( $opts['version'] ); + + // Get a collection name to describe this class of key + $kClass = $this->determineKeyClass( $key ); + + // Get the current key value + $curTTL = null; + $cValue = $this->get( $key, $curTTL, $checkKeys, $asOf ); // current value + $value = $cValue; // return value + + $preCallbackTime = $this->getCurrentTime(); + // Determine if a cached value regeneration is needed or desired + if ( $value !== false + && $this->isAliveOrInGracePeriod( $curTTL, $graceTTL ) + && $this->isValid( $value, $versioned, $asOf, $minTime ) + ) { + $preemptiveRefresh = ( + $this->worthRefreshExpiring( $curTTL, $lowTTL ) || + $this->worthRefreshPopular( $asOf, $ageNew, $popWindow, $preCallbackTime ) + ); + + if ( !$preemptiveRefresh ) { + $this->stats->increment( "wanobjectcache.$kClass.hit.good" ); + + return $value; + } elseif ( $this->asyncHandler ) { + // Update the cache value later, such during post-send of an HTTP request + $func = $this->asyncHandler; + $func( function () use ( $key, $ttl, $callback, $opts, $asOf ) { + $opts['minAsOf'] = INF; // force a refresh + $this->doGetWithSetCallback( $key, $ttl, $callback, $opts, $asOf ); + } ); + $this->stats->increment( "wanobjectcache.$kClass.hit.refresh" ); + + return $value; + } + } + + // A deleted key with a negative TTL left must be tombstoned + $isTombstone = ( $curTTL !== null && $value === false ); + if ( $isTombstone && $lockTSE <= 0 ) { + // Use the INTERIM value for tombstoned keys to reduce regeneration load + $lockTSE = self::INTERIM_KEY_TTL; + } + // Assume a key is hot if requested soon after invalidation + $isHot = ( $curTTL !== null && $curTTL <= 0 && abs( $curTTL ) <= $lockTSE ); + // Use the mutex if there is no value and a busy fallback is given + $checkBusy = ( $busyValue !== null && $value === false ); + // Decide whether a single thread should handle regenerations. + // This avoids stampedes when $checkKeys are bumped and when preemptive + // renegerations take too long. It also reduces regenerations while $key + // is tombstoned. This balances cache freshness with avoiding DB load. + $useMutex = ( $isHot || ( $isTombstone && $lockTSE > 0 ) || $checkBusy ); + + $lockAcquired = false; + if ( $useMutex ) { + // Acquire a datacenter-local non-blocking lock + if ( $this->cache->add( self::MUTEX_KEY_PREFIX . $key, 1, self::LOCK_TTL ) ) { + // Lock acquired; this thread should update the key + $lockAcquired = true; + } elseif ( $value !== false && $this->isValid( $value, $versioned, $asOf, $minTime ) ) { + $this->stats->increment( "wanobjectcache.$kClass.hit.stale" ); + // If it cannot be acquired; then the stale value can be used + return $value; + } else { + // Use the INTERIM value for tombstoned keys to reduce regeneration load. + // For hot keys, either another thread has the lock or the lock failed; + // use the INTERIM value from the last thread that regenerated it. + $value = $this->getInterimValue( $key, $versioned, $minTime, $asOf ); + if ( $value !== false ) { + $this->stats->increment( "wanobjectcache.$kClass.hit.volatile" ); + + return $value; + } + // Use the busy fallback value if nothing else + if ( $busyValue !== null ) { + $this->stats->increment( "wanobjectcache.$kClass.miss.busy" ); + + return is_callable( $busyValue ) ? $busyValue() : $busyValue; + } + } + } + + if ( !is_callable( $callback ) ) { + throw new InvalidArgumentException( "Invalid cache miss callback provided." ); + } + + // Generate the new value from the callback... + $setOpts = []; + ++$this->callbackDepth; + try { + $value = call_user_func_array( $callback, [ $cValue, &$ttl, &$setOpts, $asOf ] ); + } finally { + --$this->callbackDepth; + } + $valueIsCacheable = ( $value !== false && $ttl >= 0 ); + + // When delete() is called, writes are write-holed by the tombstone, + // so use a special INTERIM key to pass the new value around threads. + if ( ( $isTombstone && $lockTSE > 0 ) && $valueIsCacheable ) { + $tempTTL = max( 1, (int)$lockTSE ); // set() expects seconds + $newAsOf = $this->getCurrentTime(); + $wrapped = $this->wrap( $value, $tempTTL, $newAsOf ); + // Avoid using set() to avoid pointless mcrouter broadcasting + $this->setInterimValue( $key, $wrapped, $tempTTL ); + } + + if ( $valueIsCacheable ) { + $setOpts['lockTSE'] = $lockTSE; + $setOpts['staleTTL'] = $staleTTL; + // Use best known "since" timestamp if not provided + $setOpts += [ 'since' => $preCallbackTime ]; + // Update the cache; this will fail if the key is tombstoned + $this->set( $key, $value, $ttl, $setOpts ); + } + + if ( $lockAcquired ) { + // Avoid using delete() to avoid pointless mcrouter broadcasting + $this->cache->changeTTL( self::MUTEX_KEY_PREFIX . $key, (int)$preCallbackTime - 60 ); + } + + $this->stats->increment( "wanobjectcache.$kClass.miss.compute" ); + + return $value; + } + + /** + * @param string $key + * @param bool $versioned + * @param float $minTime + * @param mixed &$asOf + * @return mixed + */ + protected function getInterimValue( $key, $versioned, $minTime, &$asOf ) { + if ( !$this->useInterimHoldOffCaching ) { + return false; // disabled + } + + $wrapped = $this->cache->get( self::INTERIM_KEY_PREFIX . $key ); + list( $value ) = $this->unwrap( $wrapped, $this->getCurrentTime() ); + if ( $value !== false && $this->isValid( $value, $versioned, $asOf, $minTime ) ) { + $asOf = $wrapped[self::FLD_TIME]; + + return $value; + } + + return false; + } + + /** + * @param string $key + * @param array $wrapped + * @param int $tempTTL + */ + protected function setInterimValue( $key, $wrapped, $tempTTL ) { + $this->cache->merge( + self::INTERIM_KEY_PREFIX . $key, + function () use ( $wrapped ) { + return $wrapped; + }, + $tempTTL, + 1 + ); + } + + /** + * Method to fetch multiple cache keys at once with regeneration + * + * This works the same as getWithSetCallback() except: + * - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys() + * - b) The $callback argument expects a callback taking the following arguments: + * - $id: ID of an entity to query + * - $oldValue : the prior cache value or false if none was present + * - &$ttl : a reference to the new value TTL in seconds + * - &$setOpts : a reference to options for set() which can be altered + * - $oldAsOf : generation UNIX timestamp of $oldValue or null if not present + * Aside from the additional $id argument, the other arguments function the same + * way they do in getWithSetCallback(). + * - c) The return value is a map of (cache key => value) in the order of $keyedIds + * + * @see WANObjectCache::getWithSetCallback() + * @see WANObjectCache::getMultiWithUnionSetCallback() + * + * Example usage: + * @code + * $rows = $cache->getMultiWithSetCallback( + * // Map of cache keys to entity IDs + * $cache->makeMultiKeys( + * $this->fileVersionIds(), + * function ( $id, WANObjectCache $cache ) { + * return $cache->makeKey( 'file-version', $id ); + * } + * ), + * // Time-to-live (in seconds) + * $cache::TTL_DAY, + * // Function that derives the new key value + * function ( $id, $oldValue, &$ttl, array &$setOpts ) { + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * // Load the row for this file + * $queryInfo = File::getQueryInfo(); + * $row = $dbr->selectRow( + * $queryInfo['tables'], + * $queryInfo['fields'], + * [ 'id' => $id ], + * __METHOD__, + * [], + * $queryInfo['joins'] + * ); + * + * return $row ? (array)$row : false; + * }, + * [ + * // Process cache for 30 seconds + * 'pcTTL' => 30, + * // Use a dedicated 500 item cache (initialized on-the-fly) + * 'pcGroup' => 'file-versions:500' + * ] + * ); + * $files = array_map( [ __CLASS__, 'newFromRow' ], $rows ); + * @endcode + * + * @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys() + * @param int $ttl Seconds to live for key updates + * @param callable $callback Callback the yields entity regeneration callbacks + * @param array $opts Options map + * @return array Map of (cache key => value) in the same order as $keyedIds + * @since 1.28 + */ + final public function getMultiWithSetCallback( + ArrayIterator $keyedIds, $ttl, callable $callback, array $opts = [] + ) { + $valueKeys = array_keys( $keyedIds->getArrayCopy() ); + $checkKeys = isset( $opts['checkKeys'] ) ? $opts['checkKeys'] : []; + + // Load required keys into process cache in one go + $this->warmupCache = $this->getRawKeysForWarmup( + $this->getNonProcessCachedKeys( $valueKeys, $opts ), + $checkKeys + ); + $this->warmupKeyMisses = 0; + + // Wrap $callback to match the getWithSetCallback() format while passing $id to $callback + $id = null; // current entity ID + $func = function ( $oldValue, &$ttl, &$setOpts, $oldAsOf ) use ( $callback, &$id ) { + return $callback( $id, $oldValue, $ttl, $setOpts, $oldAsOf ); + }; + + $values = []; + foreach ( $keyedIds as $key => $id ) { // preserve order + $values[$key] = $this->getWithSetCallback( $key, $ttl, $func, $opts ); + } + + $this->warmupCache = []; + + return $values; + } + + /** + * Method to fetch/regenerate multiple cache keys at once + * + * This works the same as getWithSetCallback() except: + * - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys() + * - b) The $callback argument expects a callback returning a map of (ID => new value) + * for all entity IDs in $ids and it takes the following arguments: + * - $ids: a list of entity IDs that require cache regeneration + * - &$ttls: a reference to the (entity ID => new TTL) map + * - &$setOpts: a reference to options for set() which can be altered + * - c) The return value is a map of (cache key => value) in the order of $keyedIds + * - d) The "lockTSE" and "busyValue" options are ignored + * + * @see WANObjectCache::getWithSetCallback() + * @see WANObjectCache::getMultiWithSetCallback() + * + * Example usage: + * @code + * $rows = $cache->getMultiWithUnionSetCallback( + * // Map of cache keys to entity IDs + * $cache->makeMultiKeys( + * $this->fileVersionIds(), + * function ( $id, WANObjectCache $cache ) { + * return $cache->makeKey( 'file-version', $id ); + * } + * ), + * // Time-to-live (in seconds) + * $cache::TTL_DAY, + * // Function that derives the new key value + * function ( array $ids, array &$ttls, array &$setOpts ) { + * $dbr = wfGetDB( DB_REPLICA ); + * // Account for any snapshot/replica DB lag + * $setOpts += Database::getCacheSetOptions( $dbr ); + * + * // Load the rows for these files + * $rows = []; + * $queryInfo = File::getQueryInfo(); + * $res = $dbr->select( + * $queryInfo['tables'], + * $queryInfo['fields'], + * [ 'id' => $ids ], + * __METHOD__, + * [], + * $queryInfo['joins'] + * ); + * foreach ( $res as $row ) { + * $rows[$row->id] = $row; + * $mtime = wfTimestamp( TS_UNIX, $row->timestamp ); + * $ttls[$row->id] = $this->adaptiveTTL( $mtime, $ttls[$row->id] ); + * } + * + * return $rows; + * }, + * ] + * ); + * $files = array_map( [ __CLASS__, 'newFromRow' ], $rows ); + * @endcode + * + * @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys() + * @param int $ttl Seconds to live for key updates + * @param callable $callback Callback the yields entity regeneration callbacks + * @param array $opts Options map + * @return array Map of (cache key => value) in the same order as $keyedIds + * @since 1.30 + */ + final public function getMultiWithUnionSetCallback( + ArrayIterator $keyedIds, $ttl, callable $callback, array $opts = [] + ) { + $idsByValueKey = $keyedIds->getArrayCopy(); + $valueKeys = array_keys( $idsByValueKey ); + $checkKeys = isset( $opts['checkKeys'] ) ? $opts['checkKeys'] : []; + unset( $opts['lockTSE'] ); // incompatible + unset( $opts['busyValue'] ); // incompatible + + // Load required keys into process cache in one go + $keysGet = $this->getNonProcessCachedKeys( $valueKeys, $opts ); + $this->warmupCache = $this->getRawKeysForWarmup( $keysGet, $checkKeys ); + $this->warmupKeyMisses = 0; + + // IDs of entities known to be in need of regeneration + $idsRegen = []; + + // Find out which keys are missing/deleted/stale + $curTTLs = []; + $asOfs = []; + $curByKey = $this->getMulti( $keysGet, $curTTLs, $checkKeys, $asOfs ); + foreach ( $keysGet as $key ) { + if ( !array_key_exists( $key, $curByKey ) || $curTTLs[$key] < 0 ) { + $idsRegen[] = $idsByValueKey[$key]; + } + } + + // Run the callback to populate the regeneration value map for all required IDs + $newSetOpts = []; + $newTTLsById = array_fill_keys( $idsRegen, $ttl ); + $newValsById = $idsRegen ? $callback( $idsRegen, $newTTLsById, $newSetOpts ) : []; + + // Wrap $callback to match the getWithSetCallback() format while passing $id to $callback + $id = null; // current entity ID + $func = function ( $oldValue, &$ttl, &$setOpts, $oldAsOf ) + use ( $callback, &$id, $newValsById, $newTTLsById, $newSetOpts ) + { + if ( array_key_exists( $id, $newValsById ) ) { + // Value was already regerated as expected, so use the value in $newValsById + $newValue = $newValsById[$id]; + $ttl = $newTTLsById[$id]; + $setOpts = $newSetOpts; + } else { + // Pre-emptive/popularity refresh and version mismatch cases are not detected + // above and thus $newValsById has no entry. Run $callback on this single entity. + $ttls = [ $id => $ttl ]; + $newValue = $callback( [ $id ], $ttls, $setOpts )[$id]; + $ttl = $ttls[$id]; + } + + return $newValue; + }; + + // Run the cache-aside logic using warmupCache instead of persistent cache queries + $values = []; + foreach ( $idsByValueKey as $key => $id ) { // preserve order + $values[$key] = $this->getWithSetCallback( $key, $ttl, $func, $opts ); + } + + $this->warmupCache = []; + + return $values; + } + + /** + * Set a key to soon expire in the local cluster if it pre-dates $purgeTimestamp + * + * This sets stale keys' time-to-live at HOLDOFF_TTL seconds, which both avoids + * broadcasting in mcrouter setups and also avoids races with new tombstones. + * + * @param string $key Cache key + * @param int $purgeTimestamp UNIX timestamp of purge + * @param bool &$isStale Whether the key is stale + * @return bool Success + * @since 1.28 + */ + final public function reap( $key, $purgeTimestamp, &$isStale = false ) { + $minAsOf = $purgeTimestamp + self::HOLDOFF_TTL; + $wrapped = $this->cache->get( self::VALUE_KEY_PREFIX . $key ); + if ( is_array( $wrapped ) && $wrapped[self::FLD_TIME] < $minAsOf ) { + $isStale = true; + $this->logger->warning( "Reaping stale value key '$key'." ); + $ttlReap = self::HOLDOFF_TTL; // avoids races with tombstone creation + $ok = $this->cache->changeTTL( self::VALUE_KEY_PREFIX . $key, $ttlReap ); + if ( !$ok ) { + $this->logger->error( "Could not complete reap of key '$key'." ); + } + + return $ok; + } + + $isStale = false; + + return true; + } + + /** + * Set a "check" key to soon expire in the local cluster if it pre-dates $purgeTimestamp + * + * @param string $key Cache key + * @param int $purgeTimestamp UNIX timestamp of purge + * @param bool &$isStale Whether the key is stale + * @return bool Success + * @since 1.28 + */ + final public function reapCheckKey( $key, $purgeTimestamp, &$isStale = false ) { + $purge = $this->parsePurgeValue( $this->cache->get( self::TIME_KEY_PREFIX . $key ) ); + if ( $purge && $purge[self::FLD_TIME] < $purgeTimestamp ) { + $isStale = true; + $this->logger->warning( "Reaping stale check key '$key'." ); + $ok = $this->cache->changeTTL( self::TIME_KEY_PREFIX . $key, self::TTL_SECOND ); + if ( !$ok ) { + $this->logger->error( "Could not complete reap of check key '$key'." ); + } + + return $ok; + } + + $isStale = false; + + return false; + } + + /** + * @see BagOStuff::makeKey() + * @param string $class Key class + * @param string $component [optional] Key component (starting with a key collection name) + * @return string Colon-delimited list of $keyspace followed by escaped components of $args + * @since 1.27 + */ + public function makeKey( $class, $component = null ) { + return call_user_func_array( [ $this->cache, __FUNCTION__ ], func_get_args() ); + } + + /** + * @see BagOStuff::makeGlobalKey() + * @param string $class Key class + * @param string $component [optional] Key component (starting with a key collection name) + * @return string Colon-delimited list of $keyspace followed by escaped components of $args + * @since 1.27 + */ + public function makeGlobalKey( $class, $component = null ) { + return call_user_func_array( [ $this->cache, __FUNCTION__ ], func_get_args() ); + } + + /** + * @param array $entities List of entity IDs + * @param callable $keyFunc Callback yielding a key from (entity ID, this WANObjectCache) + * @return ArrayIterator Iterator yielding (cache key => entity ID) in $entities order + * @since 1.28 + */ + final public function makeMultiKeys( array $entities, callable $keyFunc ) { + $map = []; + foreach ( $entities as $entity ) { + $map[$keyFunc( $entity, $this )] = $entity; + } + + return new ArrayIterator( $map ); + } + + /** + * Get the "last error" registered; clearLastError() should be called manually + * @return int ERR_* class constant for the "last error" registry + */ + final public function getLastError() { + if ( $this->lastRelayError ) { + // If the cache and the relayer failed, focus on the latter. + // An update not making it to the relayer means it won't show up + // in other DCs (nor will consistent re-hashing see up-to-date values). + // On the other hand, if just the cache update failed, then it should + // eventually be applied by the relayer. + return $this->lastRelayError; + } + + $code = $this->cache->getLastError(); + switch ( $code ) { + case BagOStuff::ERR_NONE: + return self::ERR_NONE; + case BagOStuff::ERR_NO_RESPONSE: + return self::ERR_NO_RESPONSE; + case BagOStuff::ERR_UNREACHABLE: + return self::ERR_UNREACHABLE; + default: + return self::ERR_UNEXPECTED; + } + } + + /** + * Clear the "last error" registry + */ + final public function clearLastError() { + $this->cache->clearLastError(); + $this->lastRelayError = self::ERR_NONE; + } + + /** + * Clear the in-process caches; useful for testing + * + * @since 1.27 + */ + public function clearProcessCache() { + $this->processCaches = []; + } + + /** + * Enable or disable the use of brief caching for tombstoned keys + * + * When a key is purged via delete(), there normally is a period where caching + * is hold-off limited to an extremely short time. This method will disable that + * caching, forcing the callback to run for any of: + * - WANObjectCache::getWithSetCallback() + * - WANObjectCache::getMultiWithSetCallback() + * - WANObjectCache::getMultiWithUnionSetCallback() + * + * This is useful when both: + * - a) the database used by the callback is known to be up-to-date enough + * for some particular purpose (e.g. replica DB has applied transaction X) + * - b) the caller needs to exploit that fact, and therefore needs to avoid the + * use of inherently volatile and possibly stale interim keys + * + * @see WANObjectCache::delete() + * @param bool $enabled Whether to enable interim caching + * @since 1.31 + */ + final public function useInterimHoldOffCaching( $enabled ) { + $this->useInterimHoldOffCaching = $enabled; + } + + /** + * @param int $flag ATTR_* class constant + * @return int QOS_* class constant + * @since 1.28 + */ + public function getQoS( $flag ) { + return $this->cache->getQoS( $flag ); + } + + /** + * Get a TTL that is higher for objects that have not changed recently + * + * This is useful for keys that get explicit purges and DB or purge relay + * lag is a potential concern (especially how it interacts with CDN cache) + * + * Example usage: + * @code + * // Last-modified time of page + * $mtime = wfTimestamp( TS_UNIX, $page->getTimestamp() ); + * // Get adjusted TTL. If $mtime is 3600 seconds ago and $minTTL/$factor left at + * // defaults, then $ttl is 3600 * .2 = 720. If $minTTL was greater than 720, then + * // $ttl would be $minTTL. If $maxTTL was smaller than 720, $ttl would be $maxTTL. + * $ttl = $cache->adaptiveTTL( $mtime, $cache::TTL_DAY ); + * @endcode + * + * Another use case is when there are no applicable "last modified" fields in the DB, + * and there are too many dependencies for explicit purges to be viable, and the rate of + * change to relevant content is unstable, and it is highly valued to have the cached value + * be as up-to-date as possible. + * + * Example usage: + * @code + * $query = "<some complex query>"; + * $idListFromComplexQuery = $cache->getWithSetCallback( + * $cache->makeKey( 'complex-graph-query', $hashOfQuery ), + * GraphQueryClass::STARTING_TTL, + * function ( $oldValue, &$ttl, array &$setOpts, $oldAsOf ) use ( $query, $cache ) { + * $gdb = $this->getReplicaGraphDbConnection(); + * // Account for any snapshot/replica DB lag + * $setOpts += GraphDatabase::getCacheSetOptions( $gdb ); + * + * $newList = iterator_to_array( $gdb->query( $query ) ); + * sort( $newList, SORT_NUMERIC ); // normalize + * + * $minTTL = GraphQueryClass::MIN_TTL; + * $maxTTL = GraphQueryClass::MAX_TTL; + * if ( $oldValue !== false ) { + * // Note that $oldAsOf is the last time this callback ran + * $ttl = ( $newList === $oldValue ) + * // No change: cache for 150% of the age of $oldValue + * ? $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, 1.5 ) + * // Changed: cache for 50% of the age of $oldValue + * : $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, .5 ); + * } + * + * return $newList; + * }, + * [ + * // Keep stale values around for doing comparisons for TTL calculations. + * // High values improve long-tail keys hit-rates, though might waste space. + * 'staleTTL' => GraphQueryClass::GRACE_TTL + * ] + * ); + * @endcode + * + * @param int|float $mtime UNIX timestamp + * @param int $maxTTL Maximum TTL (seconds) + * @param int $minTTL Minimum TTL (seconds); Default: 30 + * @param float $factor Value in the range (0,1); Default: .2 + * @return int Adaptive TTL + * @since 1.28 + */ + public function adaptiveTTL( $mtime, $maxTTL, $minTTL = 30, $factor = 0.2 ) { + if ( is_float( $mtime ) || ctype_digit( $mtime ) ) { + $mtime = (int)$mtime; // handle fractional seconds and string integers + } + + if ( !is_int( $mtime ) || $mtime <= 0 ) { + return $minTTL; // no last-modified time provided + } + + $age = $this->getCurrentTime() - $mtime; + + return (int)min( $maxTTL, max( $minTTL, $factor * $age ) ); + } + + /** + * @return int Number of warmup key cache misses last round + * @since 1.30 + */ + final public function getWarmupKeyMisses() { + return $this->warmupKeyMisses; + } + + /** + * Do the actual async bus purge of a key + * + * This must set the key to "PURGED:<UNIX timestamp>:<holdoff>" + * + * @param string $key Cache key + * @param int $ttl How long to keep the tombstone [seconds] + * @param int $holdoff HOLDOFF_* constant controlling how long to ignore sets for this key + * @return bool Success + */ + protected function relayPurge( $key, $ttl, $holdoff ) { + if ( $this->mcrouterAware ) { + // See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup + // Wildcards select all matching routes, e.g. the WAN cluster on all DCs + $ok = $this->cache->set( + "/*/{$this->cluster}/{$key}", + $this->makePurgeValue( $this->getCurrentTime(), self::HOLDOFF_NONE ), + $ttl + ); + } elseif ( $this->purgeRelayer instanceof EventRelayerNull ) { + // This handles the mcrouter and the single-DC case + $ok = $this->cache->set( + $key, + $this->makePurgeValue( $this->getCurrentTime(), self::HOLDOFF_NONE ), + $ttl + ); + } else { + $event = $this->cache->modifySimpleRelayEvent( [ + 'cmd' => 'set', + 'key' => $key, + 'val' => 'PURGED:$UNIXTIME$:' . (int)$holdoff, + 'ttl' => max( $ttl, self::TTL_SECOND ), + 'sbt' => true, // substitute $UNIXTIME$ with actual microtime + ] ); + + $ok = $this->purgeRelayer->notify( $this->purgeChannel, $event ); + if ( !$ok ) { + $this->lastRelayError = self::ERR_RELAY; + } + } + + return $ok; + } + + /** + * Do the actual async bus delete of a key + * + * @param string $key Cache key + * @return bool Success + */ + protected function relayDelete( $key ) { + if ( $this->mcrouterAware ) { + // See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup + // Wildcards select all matching routes, e.g. the WAN cluster on all DCs + $ok = $this->cache->delete( "/*/{$this->cluster}/{$key}" ); + } elseif ( $this->purgeRelayer instanceof EventRelayerNull ) { + // Some other proxy handles broadcasting or there is only one datacenter + $ok = $this->cache->delete( $key ); + } else { + $event = $this->cache->modifySimpleRelayEvent( [ + 'cmd' => 'delete', + 'key' => $key, + ] ); + + $ok = $this->purgeRelayer->notify( $this->purgeChannel, $event ); + if ( !$ok ) { + $this->lastRelayError = self::ERR_RELAY; + } + } + + return $ok; + } + + /** + * Check if a key is fresh or in the grace window and thus due for randomized reuse + * + * If $curTTL > 0 (e.g. not expired) this returns true. Otherwise, the chance of returning + * true decrease steadily from 100% to 0% as the |$curTTL| moves from 0 to $graceTTL seconds. + * This handles widely varying levels of cache access traffic. + * + * If $curTTL <= -$graceTTL (e.g. already expired), then this returns false. + * + * @param float $curTTL Approximate TTL left on the key if present + * @param int $graceTTL Consider using stale values if $curTTL is greater than this + * @return bool + */ + protected function isAliveOrInGracePeriod( $curTTL, $graceTTL ) { + if ( $curTTL > 0 ) { + return true; + } elseif ( $graceTTL <= 0 ) { + return false; + } + + $ageStale = abs( $curTTL ); // seconds of staleness + $curGTTL = ( $graceTTL - $ageStale ); // current grace-time-to-live + if ( $curGTTL <= 0 ) { + return false; // already out of grace period + } + + // Chance of using a stale value is the complement of the chance of refreshing it + return !$this->worthRefreshExpiring( $curGTTL, $graceTTL ); + } + + /** + * Check if a key is nearing expiration and thus due for randomized regeneration + * + * This returns false if $curTTL >= $lowTTL. Otherwise, the chance of returning true + * increases steadily from 0% to 100% as the $curTTL moves from $lowTTL to 0 seconds. + * This handles widely varying levels of cache access traffic. + * + * If $curTTL <= 0 (e.g. already expired), then this returns false. + * + * @param float $curTTL Approximate TTL left on the key if present + * @param float $lowTTL Consider a refresh when $curTTL is less than this + * @return bool + */ + protected function worthRefreshExpiring( $curTTL, $lowTTL ) { + if ( $lowTTL <= 0 ) { + return false; + } elseif ( $curTTL >= $lowTTL ) { + return false; + } elseif ( $curTTL <= 0 ) { + return false; + } + + $chance = ( 1 - $curTTL / $lowTTL ); + + return mt_rand( 1, 1e9 ) <= 1e9 * $chance; + } + + /** + * Check if a key is due for randomized regeneration due to its popularity + * + * This is used so that popular keys can preemptively refresh themselves for higher + * consistency (especially in the case of purge loss/delay). Unpopular keys can remain + * in cache with their high nominal TTL. This means popular keys keep good consistency, + * whether the data changes frequently or not, and long-tail keys get to stay in cache + * and get hits too. Similar to worthRefreshExpiring(), randomization is used. + * + * @param float $asOf UNIX timestamp of the value + * @param int $ageNew Age of key when this might recommend refreshing (seconds) + * @param int $timeTillRefresh Age of key when it should be refreshed if popular (seconds) + * @param float $now The current UNIX timestamp + * @return bool + */ + protected function worthRefreshPopular( $asOf, $ageNew, $timeTillRefresh, $now ) { + if ( $ageNew < 0 || $timeTillRefresh <= 0 ) { + return false; + } + + $age = $now - $asOf; + $timeOld = $age - $ageNew; + if ( $timeOld <= 0 ) { + return false; + } + + // Lifecycle is: new, ramp-up refresh chance, full refresh chance. + // Note that the "expected # of refreshes" for the ramp-up time range is half of what it + // would be if P(refresh) was at its full value during that time range. + $refreshWindowSec = max( $timeTillRefresh - $ageNew - self::RAMPUP_TTL / 2, 1 ); + // P(refresh) * (# hits in $refreshWindowSec) = (expected # of refreshes) + // P(refresh) * ($refreshWindowSec * $popularHitsPerSec) = 1 + // P(refresh) = 1/($refreshWindowSec * $popularHitsPerSec) + $chance = 1 / ( self::HIT_RATE_HIGH * $refreshWindowSec ); + + // Ramp up $chance from 0 to its nominal value over RAMPUP_TTL seconds to avoid stampedes + $chance *= ( $timeOld <= self::RAMPUP_TTL ) ? $timeOld / self::RAMPUP_TTL : 1; + + return mt_rand( 1, 1e9 ) <= 1e9 * $chance; + } + + /** + * Check whether $value is appropriately versioned and not older than $minTime (if set) + * + * @param array $value + * @param bool $versioned + * @param float $asOf The time $value was generated + * @param float $minTime The last time the main value was generated (0.0 if unknown) + * @return bool + */ + protected function isValid( $value, $versioned, $asOf, $minTime ) { + if ( $versioned && !isset( $value[self::VFLD_VERSION] ) ) { + return false; + } elseif ( $minTime > 0 && $asOf < $minTime ) { + return false; + } + + return true; + } + + /** + * Do not use this method outside WANObjectCache + * + * @param mixed $value + * @param int $ttl [0=forever] + * @param float $now Unix Current timestamp just before calling set() + * @return array + */ + protected function wrap( $value, $ttl, $now ) { + return [ + self::FLD_VERSION => self::VERSION, + self::FLD_VALUE => $value, + self::FLD_TTL => $ttl, + self::FLD_TIME => $now + ]; + } + + /** + * Do not use this method outside WANObjectCache + * + * @param array|string|bool $wrapped + * @param float $now Unix Current timestamp (preferrably pre-query) + * @return array (mixed; false if absent/tombstoned/invalid, current time left) + */ + protected function unwrap( $wrapped, $now ) { + // Check if the value is a tombstone + $purge = $this->parsePurgeValue( $wrapped ); + if ( $purge !== false ) { + // Purged values should always have a negative current $ttl + $curTTL = min( $purge[self::FLD_TIME] - $now, self::TINY_NEGATIVE ); + return [ false, $curTTL ]; + } + + if ( !is_array( $wrapped ) // not found + || !isset( $wrapped[self::FLD_VERSION] ) // wrong format + || $wrapped[self::FLD_VERSION] !== self::VERSION // wrong version + ) { + return [ false, null ]; + } + + $flags = isset( $wrapped[self::FLD_FLAGS] ) ? $wrapped[self::FLD_FLAGS] : 0; + if ( ( $flags & self::FLG_STALE ) == self::FLG_STALE ) { + // Treat as expired, with the cache time as the expiration + $age = $now - $wrapped[self::FLD_TIME]; + $curTTL = min( -$age, self::TINY_NEGATIVE ); + } elseif ( $wrapped[self::FLD_TTL] > 0 ) { + // Get the approximate time left on the key + $age = $now - $wrapped[self::FLD_TIME]; + $curTTL = max( $wrapped[self::FLD_TTL] - $age, 0.0 ); + } else { + // Key had no TTL, so the time left is unbounded + $curTTL = INF; + } + + return [ $wrapped[self::FLD_VALUE], $curTTL ]; + } + + /** + * @param array $keys + * @param string $prefix + * @return string[] + */ + protected static function prefixCacheKeys( array $keys, $prefix ) { + $res = []; + foreach ( $keys as $key ) { + $res[] = $prefix . $key; + } + + return $res; + } + + /** + * @param string $key String of the format <scope>:<class>[:<class or variable>]... + * @return string + */ + protected function determineKeyClass( $key ) { + $parts = explode( ':', $key ); + + return isset( $parts[1] ) ? $parts[1] : $parts[0]; // sanity + } + + /** + * @param string $value Wrapped value like "PURGED:<timestamp>:<holdoff>" + * @return array|bool Array containing a UNIX timestamp (float) and holdoff period (integer), + * or false if value isn't a valid purge value + */ + protected function parsePurgeValue( $value ) { + if ( !is_string( $value ) ) { + return false; + } + $segments = explode( ':', $value, 3 ); + if ( !isset( $segments[0] ) || !isset( $segments[1] ) + || "{$segments[0]}:" !== self::PURGE_VAL_PREFIX + ) { + return false; + } + if ( !isset( $segments[2] ) ) { + // Back-compat with old purge values without holdoff + $segments[2] = self::HOLDOFF_TTL; + } + return [ + self::FLD_TIME => (float)$segments[1], + self::FLD_HOLDOFF => (int)$segments[2], + ]; + } + + /** + * @param float $timestamp + * @param int $holdoff In seconds + * @return string Wrapped purge value + */ + protected function makePurgeValue( $timestamp, $holdoff ) { + return self::PURGE_VAL_PREFIX . (float)$timestamp . ':' . (int)$holdoff; + } + + /** + * @param string $group + * @return HashBagOStuff + */ + protected function getProcessCache( $group ) { + if ( !isset( $this->processCaches[$group] ) ) { + list( , $n ) = explode( ':', $group ); + $this->processCaches[$group] = new HashBagOStuff( [ 'maxKeys' => (int)$n ] ); + } + + return $this->processCaches[$group]; + } + + /** + * @param array $keys + * @param array $opts + * @return array List of keys + */ + private function getNonProcessCachedKeys( array $keys, array $opts ) { + $keysFound = []; + if ( isset( $opts['pcTTL'] ) && $opts['pcTTL'] > 0 && $this->callbackDepth == 0 ) { + $pcGroup = isset( $opts['pcGroup'] ) ? $opts['pcGroup'] : self::PC_PRIMARY; + $procCache = $this->getProcessCache( $pcGroup ); + foreach ( $keys as $key ) { + if ( $procCache->get( $key ) !== false ) { + $keysFound[] = $key; + } + } + } + + return array_diff( $keys, $keysFound ); + } + + /** + * @param array $keys + * @param array $checkKeys + * @return array Map of (cache key => mixed) + */ + private function getRawKeysForWarmup( array $keys, array $checkKeys ) { + if ( !$keys ) { + return []; + } + + $keysWarmUp = []; + // Get all the value keys to fetch... + foreach ( $keys as $key ) { + $keysWarmUp[] = self::VALUE_KEY_PREFIX . $key; + } + // Get all the check keys to fetch... + foreach ( $checkKeys as $i => $checkKeyOrKeys ) { + if ( is_int( $i ) ) { + // Single check key that applies to all value keys + $keysWarmUp[] = self::TIME_KEY_PREFIX . $checkKeyOrKeys; + } else { + // List of check keys that apply to value key $i + $keysWarmUp = array_merge( + $keysWarmUp, + self::prefixCacheKeys( $checkKeyOrKeys, self::TIME_KEY_PREFIX ) + ); + } + } + + $warmupCache = $this->cache->getMulti( $keysWarmUp ); + $warmupCache += array_fill_keys( $keysWarmUp, false ); + + return $warmupCache; + } + + /** + * @return float UNIX timestamp + * @codeCoverageIgnore + */ + protected function getCurrentTime() { + return $this->wallClockOverride ?: microtime( true ); + } + + /** + * @param float|null &$time Mock UNIX timestamp for testing + * @codeCoverageIgnore + */ + public function setMockTime( &$time ) { + $this->wallClockOverride =& $time; + $this->cache->setMockTime( $time ); + } +} |