1824 lines
71 KiB
PHP
1824 lines
71 KiB
PHP
<?php
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/**
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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* http://www.gnu.org/copyleft/gpl.html
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*
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* @file
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* @ingroup Cache
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*/
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use Liuggio\StatsdClient\Factory\StatsdDataFactoryInterface;
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use Psr\Log\LoggerAwareInterface;
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use Psr\Log\LoggerInterface;
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use Psr\Log\NullLogger;
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/**
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* Multi-datacenter aware caching interface
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*
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* All operations go to the local datacenter cache, except for delete(),
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* touchCheckKey(), and resetCheckKey(), which broadcast to all datacenters.
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*
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* This class is intended for caching data from primary stores.
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* If the get() method does not return a value, then the caller
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* should query the new value and backfill the cache using set().
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* The preferred way to do this logic is through getWithSetCallback().
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* When querying the store on cache miss, the closest DB replica
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* should be used. Try to avoid heavyweight DB master or quorum reads.
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* When the source data changes, a purge method should be called.
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* Since purges are expensive, they should be avoided. One can do so if:
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* - a) The object cached is immutable; or
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* - b) Validity is checked against the source after get(); or
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* - c) Using a modest TTL is reasonably correct and performant
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*
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* The simplest purge method is delete().
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*
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* There are three supported ways to handle broadcasted operations:
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* - a) Configure the 'purge' EventRelayer to point to a valid PubSub endpoint
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* that has subscribed listeners on the cache servers applying the cache updates.
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* - b) Ignore the 'purge' EventRelayer configuration (default is NullEventRelayer)
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* and set up mcrouter as the underlying cache backend, using one of the memcached
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* BagOStuff classes as 'cache'. Use OperationSelectorRoute in the mcrouter settings
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* to configure 'set' and 'delete' operations to go to all DCs via AllAsyncRoute and
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* configure other operations to go to the local DC via PoolRoute (for reference,
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* see https://github.com/facebook/mcrouter/wiki/List-of-Route-Handles).
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* - c) Ignore the 'purge' EventRelayer configuration (default is NullEventRelayer)
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* and set up dynomite as cache middleware between the web servers and either
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* memcached or redis. This will also broadcast all key setting operations, not just purges,
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* which can be useful for cache warming. Writes are eventually consistent via the
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* Dynamo replication model (see https://github.com/Netflix/dynomite).
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*
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* Broadcasted operations like delete() and touchCheckKey() are done asynchronously
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* in all datacenters this way, though the local one should likely be near immediate.
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*
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* This means that callers in all datacenters may see older values for however many
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* milliseconds that the purge took to reach that datacenter. As with any cache, this
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* should not be relied on for cases where reads are used to determine writes to source
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* (e.g. non-cache) data stores, except when reading immutable data.
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*
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* All values are wrapped in metadata arrays. Keys use a "WANCache:" prefix
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* to avoid collisions with keys that are not wrapped as metadata arrays. The
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* prefixes are as follows:
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* - a) "WANCache:v" : used for regular value keys
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* - b) "WANCache:i" : used for temporarily storing values of tombstoned keys
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* - c) "WANCache:t" : used for storing timestamp "check" keys
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* - d) "WANCache:m" : used for temporary mutex keys to avoid cache stampedes
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*
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* @ingroup Cache
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* @since 1.26
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*/
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class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
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/** @var BagOStuff The local datacenter cache */
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protected $cache;
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/** @var HashBagOStuff[] Map of group PHP instance caches */
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protected $processCaches = [];
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/** @var string Purge channel name */
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protected $purgeChannel;
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/** @var EventRelayer Bus that handles purge broadcasts */
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protected $purgeRelayer;
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/** @var LoggerInterface */
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protected $logger;
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/** @var StatsdDataFactoryInterface */
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protected $stats;
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/** @var int ERR_* constant for the "last error" registry */
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protected $lastRelayError = self::ERR_NONE;
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/** @var int Callback stack depth for getWithSetCallback() */
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private $callbackDepth = 0;
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/** @var mixed[] Temporary warm-up cache */
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private $warmupCache = [];
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/** @var int Key fetched */
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private $warmupKeyMisses = 0;
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/** Max time expected to pass between delete() and DB commit finishing */
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const MAX_COMMIT_DELAY = 3;
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/** Max replication+snapshot lag before applying TTL_LAGGED or disallowing set() */
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const MAX_READ_LAG = 7;
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/** Seconds to tombstone keys on delete() */
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const HOLDOFF_TTL = 11; // MAX_COMMIT_DELAY + MAX_READ_LAG + 1
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/** Seconds to keep dependency purge keys around */
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const CHECK_KEY_TTL = self::TTL_YEAR;
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/** Seconds to keep lock keys around */
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const LOCK_TTL = 10;
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/** Default remaining TTL at which to consider pre-emptive regeneration */
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const LOW_TTL = 30;
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/** Default time-since-expiry on a miss that makes a key "hot" */
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const LOCK_TSE = 1;
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/** Never consider performing "popularity" refreshes until a key reaches this age */
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const AGE_NEW = 60;
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/** The time length of the "popularity" refresh window for hot keys */
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const HOT_TTR = 900;
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/** Hits/second for a refresh to be expected within the "popularity" window */
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const HIT_RATE_HIGH = 1;
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/** Seconds to ramp up to the "popularity" refresh chance after a key is no longer new */
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const RAMPUP_TTL = 30;
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/** Idiom for getWithSetCallback() callbacks to avoid calling set() */
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const TTL_UNCACHEABLE = -1;
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/** Idiom for getWithSetCallback() callbacks to 'lockTSE' logic */
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const TSE_NONE = -1;
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/** Max TTL to store keys when a data sourced is lagged */
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const TTL_LAGGED = 30;
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/** Idiom for delete() for "no hold-off" */
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const HOLDOFF_NONE = 0;
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/** Idiom for getWithSetCallback() for "no minimum required as-of timestamp" */
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const MIN_TIMESTAMP_NONE = 0.0;
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/** Tiny negative float to use when CTL comes up >= 0 due to clock skew */
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const TINY_NEGATIVE = -0.000001;
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/** Cache format version number */
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const VERSION = 1;
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const FLD_VERSION = 0; // key to cache version number
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const FLD_VALUE = 1; // key to the cached value
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const FLD_TTL = 2; // key to the original TTL
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const FLD_TIME = 3; // key to the cache time
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const FLD_FLAGS = 4; // key to the flags bitfield
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const FLD_HOLDOFF = 5; // key to any hold-off TTL
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/** @var int Treat this value as expired-on-arrival */
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const FLG_STALE = 1;
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const ERR_NONE = 0; // no error
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const ERR_NO_RESPONSE = 1; // no response
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const ERR_UNREACHABLE = 2; // can't connect
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const ERR_UNEXPECTED = 3; // response gave some error
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const ERR_RELAY = 4; // relay broadcast failed
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const VALUE_KEY_PREFIX = 'WANCache:v:';
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const INTERIM_KEY_PREFIX = 'WANCache:i:';
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const TIME_KEY_PREFIX = 'WANCache:t:';
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const MUTEX_KEY_PREFIX = 'WANCache:m:';
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const PURGE_VAL_PREFIX = 'PURGED:';
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const VFLD_DATA = 'WOC:d'; // key to the value of versioned data
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const VFLD_VERSION = 'WOC:v'; // key to the version of the value present
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const PC_PRIMARY = 'primary:1000'; // process cache name and max key count
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const DEFAULT_PURGE_CHANNEL = 'wancache-purge';
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/**
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* @param array $params
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* - cache : BagOStuff object for a persistent cache
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* - channels : Map of (action => channel string). Actions include "purge".
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* - relayers : Map of (action => EventRelayer object). Actions include "purge".
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* - logger : LoggerInterface object
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* - stats : LoggerInterface object
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*/
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public function __construct( array $params ) {
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$this->cache = $params['cache'];
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$this->purgeChannel = isset( $params['channels']['purge'] )
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? $params['channels']['purge']
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: self::DEFAULT_PURGE_CHANNEL;
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$this->purgeRelayer = isset( $params['relayers']['purge'] )
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? $params['relayers']['purge']
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: new EventRelayerNull( [] );
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$this->setLogger( isset( $params['logger'] ) ? $params['logger'] : new NullLogger() );
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$this->stats = isset( $params['stats'] ) ? $params['stats'] : new NullStatsdDataFactory();
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}
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public function setLogger( LoggerInterface $logger ) {
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$this->logger = $logger;
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}
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/**
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* Get an instance that wraps EmptyBagOStuff
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*
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* @return WANObjectCache
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*/
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public static function newEmpty() {
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return new self( [
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'cache' => new EmptyBagOStuff(),
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'pool' => 'empty'
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] );
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}
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/**
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* Fetch the value of a key from cache
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*
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* If supplied, $curTTL is set to the remaining TTL (current time left):
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* - a) INF; if $key exists, has no TTL, and is not expired by $checkKeys
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* - b) float (>=0); if $key exists, has a TTL, and is not expired by $checkKeys
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* - c) float (<0); if $key is tombstoned, stale, or existing but expired by $checkKeys
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* - d) null; if $key does not exist and is not tombstoned
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*
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* If a key is tombstoned, $curTTL will reflect the time since delete().
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*
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* The timestamp of $key will be checked against the last-purge timestamp
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* of each of $checkKeys. Those $checkKeys not in cache will have the last-purge
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* initialized to the current timestamp. If any of $checkKeys have a timestamp
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* greater than that of $key, then $curTTL will reflect how long ago $key
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* became invalid. Callers can use $curTTL to know when the value is stale.
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* The $checkKeys parameter allow mass invalidations by updating a single key:
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* - a) Each "check" key represents "last purged" of some source data
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* - b) Callers pass in relevant "check" keys as $checkKeys in get()
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* - c) When the source data that "check" keys represent changes,
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* the touchCheckKey() method is called on them
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*
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* Source data entities might exists in a DB that uses snapshot isolation
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* (e.g. the default REPEATABLE-READ in innoDB). Even for mutable data, that
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* isolation can largely be maintained by doing the following:
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* - a) Calling delete() on entity change *and* creation, before DB commit
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* - b) Keeping transaction duration shorter than delete() hold-off TTL
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*
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* However, pre-snapshot values might still be seen if an update was made
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* in a remote datacenter but the purge from delete() didn't relay yet.
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*
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* Consider using getWithSetCallback() instead of get() and set() cycles.
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* That method has cache slam avoiding features for hot/expensive keys.
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*
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* @param string $key Cache key made from makeKey() or makeGlobalKey()
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* @param mixed &$curTTL Approximate TTL left on the key if present/tombstoned [returned]
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* @param array $checkKeys List of "check" keys
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* @param float &$asOf UNIX timestamp of cached value; null on failure [returned]
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* @return mixed Value of cache key or false on failure
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*/
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final public function get( $key, &$curTTL = null, array $checkKeys = [], &$asOf = null ) {
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$curTTLs = [];
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$asOfs = [];
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$values = $this->getMulti( [ $key ], $curTTLs, $checkKeys, $asOfs );
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$curTTL = isset( $curTTLs[$key] ) ? $curTTLs[$key] : null;
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$asOf = isset( $asOfs[$key] ) ? $asOfs[$key] : null;
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return isset( $values[$key] ) ? $values[$key] : false;
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}
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/**
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* Fetch the value of several keys from cache
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*
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* @see WANObjectCache::get()
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*
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* @param array $keys List of cache keys made from makeKey() or makeGlobalKey()
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* @param array &$curTTLs Map of (key => approximate TTL left) for existing keys [returned]
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* @param array $checkKeys List of check keys to apply to all $keys. May also apply "check"
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* keys to specific cache keys only by using cache keys as keys in the $checkKeys array.
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* @param float[] &$asOfs Map of (key => UNIX timestamp of cached value; null on failure)
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* @return array Map of (key => value) for keys that exist and are not tombstoned
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*/
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final public function getMulti(
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array $keys, &$curTTLs = [], array $checkKeys = [], array &$asOfs = []
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) {
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$result = [];
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$curTTLs = [];
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$asOfs = [];
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$vPrefixLen = strlen( self::VALUE_KEY_PREFIX );
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$valueKeys = self::prefixCacheKeys( $keys, self::VALUE_KEY_PREFIX );
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$checkKeysForAll = [];
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$checkKeysByKey = [];
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$checkKeysFlat = [];
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foreach ( $checkKeys as $i => $checkKeyGroup ) {
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$prefixed = self::prefixCacheKeys( (array)$checkKeyGroup, self::TIME_KEY_PREFIX );
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$checkKeysFlat = array_merge( $checkKeysFlat, $prefixed );
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// Is this check keys for a specific cache key, or for all keys being fetched?
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if ( is_int( $i ) ) {
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$checkKeysForAll = array_merge( $checkKeysForAll, $prefixed );
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} else {
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$checkKeysByKey[$i] = isset( $checkKeysByKey[$i] )
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? array_merge( $checkKeysByKey[$i], $prefixed )
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: $prefixed;
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}
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}
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// Fetch all of the raw values
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$keysGet = array_merge( $valueKeys, $checkKeysFlat );
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if ( $this->warmupCache ) {
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$wrappedValues = array_intersect_key( $this->warmupCache, array_flip( $keysGet ) );
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$keysGet = array_diff( $keysGet, array_keys( $wrappedValues ) ); // keys left to fetch
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$this->warmupKeyMisses += count( $keysGet );
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} else {
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$wrappedValues = [];
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}
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if ( $keysGet ) {
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$wrappedValues += $this->cache->getMulti( $keysGet );
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}
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// Time used to compare/init "check" keys (derived after getMulti() to be pessimistic)
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$now = microtime( true );
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// Collect timestamps from all "check" keys
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$purgeValuesForAll = $this->processCheckKeys( $checkKeysForAll, $wrappedValues, $now );
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$purgeValuesByKey = [];
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foreach ( $checkKeysByKey as $cacheKey => $checks ) {
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$purgeValuesByKey[$cacheKey] =
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$this->processCheckKeys( $checks, $wrappedValues, $now );
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}
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// Get the main cache value for each key and validate them
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foreach ( $valueKeys as $vKey ) {
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if ( !isset( $wrappedValues[$vKey] ) ) {
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continue; // not found
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}
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$key = substr( $vKey, $vPrefixLen ); // unprefix
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list( $value, $curTTL ) = $this->unwrap( $wrappedValues[$vKey], $now );
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if ( $value !== false ) {
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$result[$key] = $value;
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// Force dependant keys to be invalid for a while after purging
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// to reduce race conditions involving stale data getting cached
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$purgeValues = $purgeValuesForAll;
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if ( isset( $purgeValuesByKey[$key] ) ) {
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$purgeValues = array_merge( $purgeValues, $purgeValuesByKey[$key] );
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}
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foreach ( $purgeValues as $purge ) {
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$safeTimestamp = $purge[self::FLD_TIME] + $purge[self::FLD_HOLDOFF];
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if ( $safeTimestamp >= $wrappedValues[$vKey][self::FLD_TIME] ) {
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// How long ago this value was expired by *this* check key
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$ago = min( $purge[self::FLD_TIME] - $now, self::TINY_NEGATIVE );
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// How long ago this value was expired by *any* known check key
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$curTTL = min( $curTTL, $ago );
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}
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}
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}
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$curTTLs[$key] = $curTTL;
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$asOfs[$key] = ( $value !== false ) ? $wrappedValues[$vKey][self::FLD_TIME] : null;
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}
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return $result;
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}
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/**
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* @since 1.27
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* @param array $timeKeys List of prefixed time check keys
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* @param array $wrappedValues
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* @param float $now
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* @return array List of purge value arrays
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*/
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private function processCheckKeys( array $timeKeys, array $wrappedValues, $now ) {
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$purgeValues = [];
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foreach ( $timeKeys as $timeKey ) {
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$purge = isset( $wrappedValues[$timeKey] )
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? self::parsePurgeValue( $wrappedValues[$timeKey] )
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: false;
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if ( $purge === false ) {
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// Key is not set or invalid; regenerate
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$newVal = $this->makePurgeValue( $now, self::HOLDOFF_TTL );
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$this->cache->add( $timeKey, $newVal, self::CHECK_KEY_TTL );
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$purge = self::parsePurgeValue( $newVal );
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}
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$purgeValues[] = $purge;
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}
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return $purgeValues;
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}
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/**
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* Set the value of a key in cache
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*
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* Simply calling this method when source data changes is not valid because
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* the changes do not replicate to the other WAN sites. In that case, delete()
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* should be used instead. This method is intended for use on cache misses.
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*
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* If the data was read from a snapshot-isolated transactions (e.g. the default
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* REPEATABLE-READ in innoDB), use 'since' to avoid the following race condition:
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* - a) T1 starts
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* - b) T2 updates a row, calls delete(), and commits
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* - c) The HOLDOFF_TTL passes, expiring the delete() tombstone
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* - d) T1 reads the row and calls set() due to a cache miss
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* - e) Stale value is stuck in cache
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*
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* Setting 'lag' and 'since' help avoids keys getting stuck in stale states.
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*
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* Example usage:
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* @code
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* $dbr = wfGetDB( DB_REPLICA );
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* $setOpts = Database::getCacheSetOptions( $dbr );
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* // Fetch the row from the DB
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* $row = $dbr->selectRow( ... );
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* $key = $cache->makeKey( 'building', $buildingId );
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* $cache->set( $key, $row, $cache::TTL_DAY, $setOpts );
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* @endcode
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*
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* @param string $key Cache key
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* @param mixed $value
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* @param int $ttl Seconds to live. Special values are:
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* - WANObjectCache::TTL_INDEFINITE: Cache forever
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* @param array $opts Options map:
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* - lag : Seconds of replica DB lag. Typically, this is either the replica DB lag
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* before the data was read or, if applicable, the replica DB lag before
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* the snapshot-isolated transaction the data was read from started.
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* Use false to indicate that replication is not running.
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* Default: 0 seconds
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* - since : UNIX timestamp of the data in $value. Typically, this is either
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* the current time the data was read or (if applicable) the time when
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* the snapshot-isolated transaction the data was read from started.
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* Default: 0 seconds
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* - pending : Whether this data is possibly from an uncommitted write transaction.
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* Generally, other threads should not see values from the future and
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* they certainly should not see ones that ended up getting rolled back.
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|
* 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.
|
|
* 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: 0.
|
|
* @note Options added in 1.28: staleTTL
|
|
* @return bool Success
|
|
*/
|
|
final public function set( $key, $value, $ttl = 0, array $opts = [] ) {
|
|
$now = microtime( true );
|
|
$lockTSE = isset( $opts['lockTSE'] ) ? $opts['lockTSE'] : self::TSE_NONE;
|
|
$age = isset( $opts['since'] ) ? max( 0, $now - $opts['since'] ) : 0;
|
|
$lag = isset( $opts['lag'] ) ? $opts['lag'] : 0;
|
|
$staleTTL = isset( $opts['staleTTL'] ) ? $opts['staleTTL'] : 0;
|
|
|
|
// Do not cache potentially uncommitted data as it might get rolled back
|
|
if ( !empty( $opts['pending'] ) ) {
|
|
$this->logger->info( "Rejected set() for $key due to pending writes." );
|
|
|
|
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 $key due to snapshot lag." );
|
|
|
|
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 $key due to replication lag." );
|
|
// Case D: medium length request with medium replication lag; ignore this set()
|
|
} else {
|
|
$this->logger->info( "Rejected set() for $key due to high read lag." );
|
|
|
|
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.
|
|
*
|
|
* 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 of the check key
|
|
*/
|
|
final public function getCheckKeyTime( $key ) {
|
|
$key = self::TIME_KEY_PREFIX . $key;
|
|
|
|
$purge = self::parsePurgeValue( $this->cache->get( $key ) );
|
|
if ( $purge !== false ) {
|
|
$time = $purge[self::FLD_TIME];
|
|
} else {
|
|
// Casting assures identical floats for the next getCheckKeyTime() calls
|
|
$now = (string)microtime( true );
|
|
$this->cache->add( $key,
|
|
$this->makePurgeValue( $now, self::HOLDOFF_TTL ),
|
|
self::CHECK_KEY_TTL
|
|
);
|
|
$time = (float)$now;
|
|
}
|
|
|
|
return $time;
|
|
}
|
|
|
|
/**
|
|
* 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 field.
|
|
* When touched, the field will be updated on all cache servers.
|
|
* Keys using it via get(), getMulti(), or getWithSetCallback() will
|
|
* be invalidated. It is treated as being HOLDOFF_TTL seconds in the future
|
|
* by those methods to avoid race conditions where dependent keys get updated
|
|
* with stale values (e.g. from a DB replica DB).
|
|
*
|
|
* This is typically useful for keys with hardcoded names or in some cases
|
|
* dynamically generated names where a low number of combinations exist.
|
|
* 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 is that this does not place high TTL keys on every cache
|
|
* server, making it better for code that will cache many different keys
|
|
* and either does not use lockTSE or uses a low enough TTL anyway.
|
|
*
|
|
* This is typically useful for keys with dynamically generated names
|
|
* where a high number of combinations exist.
|
|
*
|
|
* 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
|
|
*
|
|
* @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
|
|
* - WANObjectCache::TTL_UNCACHEABLE: Do not cache at all
|
|
* @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 these keys.
|
|
* Default: [].
|
|
* - 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) for keys that average ~1 hit/second (1 Hz).
|
|
* 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. 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.
|
|
* Default: WANObjectCache::LOW_TTL.
|
|
* - ageNew: Consider popularity refreshes only once a key reaches this age in seconds.
|
|
* Default: WANObjectCache::AGE_NEW.
|
|
* @return mixed Value found or written to the key
|
|
* @note Options added in 1.28: version, busyValue, hotTTR, ageNew, pcGroup, minAsOf
|
|
* @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 )
|
|
) {
|
|
$oldData = $oldValue[self::VFLD_DATA];
|
|
} else {
|
|
// VFLD_DATA is not set if an old, unversioned, key is present
|
|
$oldData = false;
|
|
}
|
|
|
|
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(
|
|
'cache-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;
|
|
$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 = microtime( true );
|
|
// Determine if a cached value regeneration is needed or desired
|
|
if ( $value !== false
|
|
&& $curTTL > 0
|
|
&& $this->isValid( $value, $versioned, $asOf, $minTime )
|
|
&& !$this->worthRefreshExpiring( $curTTL, $lowTTL )
|
|
&& !$this->worthRefreshPopular( $asOf, $ageNew, $popWindow, $preCallbackTime )
|
|
) {
|
|
$this->stats->increment( "wanobjectcache.$kClass.hit.good" );
|
|
|
|
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 = 1;
|
|
}
|
|
// 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 = microtime( true );
|
|
$wrapped = $this->wrap( $value, $tempTTL, $newAsOf );
|
|
// Avoid using set() to avoid pointless mcrouter broadcasting
|
|
$this->setInterimValue( $key, $wrapped, $tempTTL );
|
|
}
|
|
|
|
if ( $valueIsCacheable ) {
|
|
$setOpts['lockTSE'] = $lockTSE;
|
|
// 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 ) {
|
|
$wrapped = $this->cache->get( self::INTERIM_KEY_PREFIX . $key );
|
|
list( $value ) = $this->unwrap( $wrapped, microtime( true ) );
|
|
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
|
|
* $row = $dbr->selectRow( 'file', File::selectFields(), [ 'id' => $id ], __METHOD__ );
|
|
*
|
|
* 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 $regenById and it takes the following arguments:
|
|
* - $ids: a list of entity IDs to regenerate
|
|
* - &$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 = [];
|
|
* $res = $dbr->select( 'file', File::selectFields(), [ 'id' => $ids ], __METHOD__ );
|
|
* 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;
|
|
}
|
|
|
|
/**
|
|
* Locally set a key to expire soon if it is stale based on $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
|
|
*/
|
|
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;
|
|
}
|
|
|
|
/**
|
|
* Locally set a "check" key to expire soon if it is stale based on $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
|
|
*/
|
|
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 . $key, 1 );
|
|
if ( !$ok ) {
|
|
$this->logger->error( "Could not complete reap of check key '$key'." );
|
|
}
|
|
|
|
return $ok;
|
|
}
|
|
|
|
$isStale = false;
|
|
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* @see BagOStuff::makeKey()
|
|
* @param string $keys,... 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() {
|
|
return call_user_func_array( [ $this->cache, __FUNCTION__ ], func_get_args() );
|
|
}
|
|
|
|
/**
|
|
* @see BagOStuff::makeGlobalKey()
|
|
* @param string $keys,... 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() {
|
|
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
|
|
*/
|
|
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 = [];
|
|
}
|
|
|
|
/**
|
|
* @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
|
|
*
|
|
* @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 = time() - $mtime;
|
|
|
|
return (int)min( $maxTTL, max( $minTTL, $factor * $age ) );
|
|
}
|
|
|
|
/**
|
|
* @return int Number of warmup key cache misses last round
|
|
* @since 1.30
|
|
*/
|
|
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->purgeRelayer instanceof EventRelayerNull ) {
|
|
// This handles the mcrouter and the single-DC case
|
|
$ok = $this->cache->set( $key,
|
|
$this->makePurgeValue( microtime( true ), self::HOLDOFF_NONE ),
|
|
$ttl
|
|
);
|
|
} else {
|
|
$event = $this->cache->modifySimpleRelayEvent( [
|
|
'cmd' => 'set',
|
|
'key' => $key,
|
|
'val' => 'PURGED:$UNIXTIME$:' . (int)$holdoff,
|
|
'ttl' => max( $ttl, 1 ),
|
|
'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->purgeRelayer instanceof EventRelayerNull ) {
|
|
// This handles the mcrouter and the single-DC case
|
|
$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 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.
|
|
*
|
|
* @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 ( $curTTL >= $lowTTL ) {
|
|
return false;
|
|
} elseif ( $curTTL <= 0 ) {
|
|
return true;
|
|
}
|
|
|
|
$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 ) {
|
|
$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 = self::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 static 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;
|
|
}
|
|
}
|