2657 lines
109 KiB
PHP
2657 lines
109 KiB
PHP
<?php
|
||
/**
|
||
* This program is free software; you can redistribute it and/or modify
|
||
* it under the terms of the GNU General Public License as published by
|
||
* the Free Software Foundation; either version 2 of the License, or
|
||
* (at your option) any later version.
|
||
*
|
||
* This program is distributed in the hope that it will be useful,
|
||
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
* GNU General Public License for more details.
|
||
*
|
||
* You should have received a copy of the GNU General Public License along
|
||
* with this program; if not, write to the Free Software Foundation, Inc.,
|
||
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
|
||
* http://www.gnu.org/copyleft/gpl.html
|
||
*
|
||
* @file
|
||
* @ingroup Cache
|
||
*/
|
||
|
||
use Liuggio\StatsdClient\Factory\StatsdDataFactoryInterface;
|
||
use Psr\Log\LoggerAwareInterface;
|
||
use Psr\Log\LoggerInterface;
|
||
use Psr\Log\NullLogger;
|
||
|
||
/**
|
||
* Multi-datacenter aware caching interface
|
||
*
|
||
* ### Using WANObjectCache
|
||
*
|
||
* All operations go to the local datacenter cache, except for delete(),
|
||
* touchCheckKey(), and resetCheckKey(), which broadcast to all datacenters.
|
||
*
|
||
* This class is intended for caching data from primary stores.
|
||
* If the get() method does not return a value, then the caller
|
||
* should query the new value and backfill the cache using set().
|
||
* The preferred way to do this logic is through getWithSetCallback().
|
||
* When querying the store on cache miss, the closest DB replica
|
||
* should be used. Try to avoid heavyweight DB master or quorum reads.
|
||
*
|
||
* To ensure consumers of the cache see new values in a timely manner,
|
||
* you either need to follow either the validation strategy, or the
|
||
* purge strategy.
|
||
*
|
||
* The validation strategy refers to the natural avoidance of stale data
|
||
* by one of the following means:
|
||
*
|
||
* - A) The cached value is immutable.
|
||
* If the consumer has access to an identifier that uniquely describes a value,
|
||
* cached value need not change. Instead, the key can change. This also allows
|
||
* all servers to access their perceived current version. This is important
|
||
* in context of multiple deployed versions of your application and/or cross-dc
|
||
* database replication, to ensure deterministic values without oscillation.
|
||
* - B) Validity is checked against the source after get().
|
||
* This is the inverse of A. The unique identifier is embedded inside the value
|
||
* and validated after on retreival. If outdated, the value is recomputed.
|
||
* - C) The value is cached with a modest TTL (without validation).
|
||
* If value recomputation is reasonably performant, and the value is allowed to
|
||
* be stale, one should consider using TTL only – using the value's age as
|
||
* method of validation.
|
||
*
|
||
* The purge strategy refers to the the approach whereby your application knows that
|
||
* source data has changed and can react by purging the relevant cache keys.
|
||
* As purges are expensive, this strategy should be avoided if possible.
|
||
* The simplest purge method is delete().
|
||
*
|
||
* No matter which strategy you choose, callers must not rely on updates or purges
|
||
* being immediately visible to other servers. It should be treated similarly as
|
||
* one would a database replica.
|
||
*
|
||
* The need for immediate updates should be avoided. If needed, solutions must be
|
||
* sought outside WANObjectCache.
|
||
*
|
||
* ### Deploying WANObjectCache
|
||
*
|
||
* There are two supported ways to set up broadcasted operations:
|
||
*
|
||
* - A) Set up mcrouter as the underlying cache backend, using a memcached BagOStuff class
|
||
* for the 'cache' parameter. The 'region' and 'cluster' parameters must be provided
|
||
* and 'mcrouterAware' must be set to `true`.
|
||
* Configure mcrouter as follows:
|
||
* - 1) Use Route Prefixing based on region (datacenter) and cache cluster.
|
||
* See https://github.com/facebook/mcrouter/wiki/Routing-Prefix and
|
||
* https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup.
|
||
* - 2) To increase the consistency of delete() and touchCheckKey() during cache
|
||
* server membership changes, you can use the OperationSelectorRoute to
|
||
* configure 'set' and 'delete' operations to go to all servers in the cache
|
||
* cluster, instead of just one server determined by hashing.
|
||
* See https://github.com/facebook/mcrouter/wiki/List-of-Route-Handles.
|
||
* - B) Set up dynomite as a cache middleware between the web servers and either memcached
|
||
* or redis and use it as the underlying cache backend, using a memcached BagOStuff
|
||
* class for the 'cache' parameter. This will broadcast all key setting operations,
|
||
* not just purges, which can be useful for cache warming. Writes are eventually
|
||
* consistent via the Dynamo replication model. See https://github.com/Netflix/dynomite.
|
||
*
|
||
* Broadcasted operations like delete() and touchCheckKey() are intended to run
|
||
* immediately in the local datacenter and asynchronously in remote datacenters.
|
||
*
|
||
* This means that callers in all datacenters may see older values for however many
|
||
* milliseconds that the purge took to reach that datacenter. As with any cache, this
|
||
* should not be relied on for cases where reads are used to determine writes to source
|
||
* (e.g. non-cache) data stores, except when reading immutable data.
|
||
*
|
||
* All values are wrapped in metadata arrays. Keys use a "WANCache:" prefix
|
||
* to avoid collisions with keys that are not wrapped as metadata arrays. The
|
||
* prefixes are as follows:
|
||
* - a) "WANCache:v" : used for regular value keys
|
||
* - b) "WANCache:i" : used for temporarily storing values of tombstoned keys
|
||
* - c) "WANCache:t" : used for storing timestamp "check" keys
|
||
* - d) "WANCache:m" : used for temporary mutex keys to avoid cache stampedes
|
||
*
|
||
* @ingroup Cache
|
||
* @since 1.26
|
||
*/
|
||
class WANObjectCache implements IExpiringStore, IStoreKeyEncoder, LoggerAwareInterface {
|
||
/** @var BagOStuff The local datacenter cache */
|
||
protected $cache;
|
||
/** @var MapCacheLRU[] Map of group PHP instance caches */
|
||
protected $processCaches = [];
|
||
/** @var LoggerInterface */
|
||
protected $logger;
|
||
/** @var StatsdDataFactoryInterface */
|
||
protected $stats;
|
||
/** @var callable|null Function that takes a WAN cache callback and runs it later */
|
||
protected $asyncHandler;
|
||
|
||
/** @var bool Whether to use mcrouter key prefixing for routing */
|
||
protected $mcrouterAware;
|
||
/** @var string Physical region for mcrouter use */
|
||
protected $region;
|
||
/** @var string Cache cluster name for mcrouter use */
|
||
protected $cluster;
|
||
/** @var bool Whether to use "interim" caching while keys are tombstoned */
|
||
protected $useInterimHoldOffCaching = true;
|
||
/** @var float Unix timestamp of the oldest possible valid values */
|
||
protected $epoch;
|
||
/** @var string Stable secret used for hasing long strings into key components */
|
||
protected $secret;
|
||
|
||
/** @var int Callback stack depth for getWithSetCallback() */
|
||
private $callbackDepth = 0;
|
||
/** @var mixed[] Temporary warm-up cache */
|
||
private $warmupCache = [];
|
||
/** @var int Key fetched */
|
||
private $warmupKeyMisses = 0;
|
||
|
||
/** @var float|null */
|
||
private $wallClockOverride;
|
||
|
||
/** @var int Max expected seconds to pass between delete() and DB commit finishing */
|
||
const MAX_COMMIT_DELAY = 3;
|
||
/** @var int Max expected seconds of combined lag from replication and view snapshots */
|
||
const MAX_READ_LAG = 7;
|
||
/** @var int Seconds to tombstone keys on delete() and treat as volatile after invalidation */
|
||
const HOLDOFF_TTL = self::MAX_COMMIT_DELAY + self::MAX_READ_LAG + 1;
|
||
|
||
/** @var int Idiom for getWithSetCallback() meaning "do not store the callback result" */
|
||
const TTL_UNCACHEABLE = -1;
|
||
|
||
/** @var int Consider regeneration if the key will expire within this many seconds */
|
||
const LOW_TTL = 30;
|
||
/** @var int Max TTL, in seconds, to store keys when a data sourced is lagged */
|
||
const TTL_LAGGED = 30;
|
||
|
||
/** @var int Expected time-till-refresh, in seconds, if the key is accessed once per second */
|
||
const HOT_TTR = 900;
|
||
/** @var int Minimum key age, in seconds, for expected time-till-refresh to be considered */
|
||
const AGE_NEW = 60;
|
||
|
||
/** @var int Idiom for getWithSetCallback() meaning "no cache stampede mutex required" */
|
||
const TSE_NONE = -1;
|
||
|
||
/** @var int Idiom for set()/getWithSetCallback() meaning "no post-expiration persistence" */
|
||
const STALE_TTL_NONE = 0;
|
||
/** @var int Idiom for set()/getWithSetCallback() meaning "no post-expiration grace period" */
|
||
const GRACE_TTL_NONE = 0;
|
||
/** @var int Idiom for delete()/touchCheckKey() meaning "no hold-off period" */
|
||
const HOLDOFF_TTL_NONE = 0;
|
||
/** @var int Alias for HOLDOFF_TTL_NONE (b/c) (deprecated since 1.34) */
|
||
const HOLDOFF_NONE = self::HOLDOFF_TTL_NONE;
|
||
|
||
/** @var float Idiom for getWithSetCallback() meaning "no minimum required as-of timestamp" */
|
||
const MIN_TIMESTAMP_NONE = 0.0;
|
||
|
||
/** @var string Default process cache name and max key count */
|
||
const PC_PRIMARY = 'primary:1000';
|
||
|
||
/** @var int Idion for get()/getMulti() to return extra information by reference */
|
||
const PASS_BY_REF = -1;
|
||
|
||
/** @var int Seconds to keep dependency purge keys around */
|
||
private static $CHECK_KEY_TTL = self::TTL_YEAR;
|
||
/** @var int Seconds to keep interim value keys for tombstoned keys around */
|
||
private static $INTERIM_KEY_TTL = 1;
|
||
|
||
/** @var int Seconds to keep lock keys around */
|
||
private static $LOCK_TTL = 10;
|
||
/** @var int Seconds to no-op key set() calls to avoid large blob I/O stampedes */
|
||
private static $COOLOFF_TTL = 1;
|
||
/** @var int Seconds to ramp up the chance of regeneration due to expected time-till-refresh */
|
||
private static $RAMPUP_TTL = 30;
|
||
|
||
/** @var float Tiny negative float to use when CTL comes up >= 0 due to clock skew */
|
||
private static $TINY_NEGATIVE = -0.000001;
|
||
/** @var float Tiny positive float to use when using "minTime" to assert an inequality */
|
||
private static $TINY_POSTIVE = 0.000001;
|
||
|
||
/** @var int Milliseconds of key fetch/validate/regenerate delay prone to set() stampedes */
|
||
private static $SET_DELAY_HIGH_MS = 50;
|
||
/** @var int Min millisecond set() backoff during hold-off (far less than INTERIM_KEY_TTL) */
|
||
private static $RECENT_SET_LOW_MS = 50;
|
||
/** @var int Max millisecond set() backoff during hold-off (far less than INTERIM_KEY_TTL) */
|
||
private static $RECENT_SET_HIGH_MS = 100;
|
||
|
||
/** @var int Consider value generation slow if it takes more than this many seconds */
|
||
private static $GENERATION_SLOW_SEC = 3;
|
||
|
||
/** @var int Key to the tombstone entry timestamp */
|
||
private static $PURGE_TIME = 0;
|
||
/** @var int Key to the tombstone entry hold-off TTL */
|
||
private static $PURGE_HOLDOFF = 1;
|
||
|
||
/** @var int Cache format version number */
|
||
private static $VERSION = 1;
|
||
|
||
/** @var int Key to WAN cache version number */
|
||
private static $FLD_FORMAT_VERSION = 0;
|
||
/** @var int Key to the cached value */
|
||
private static $FLD_VALUE = 1;
|
||
/** @var int Key to the original TTL */
|
||
private static $FLD_TTL = 2;
|
||
/** @var int Key to the cache timestamp */
|
||
private static $FLD_TIME = 3;
|
||
/** @var int Key to the flags bit field (reserved number) */
|
||
private static /** @noinspection PhpUnusedPrivateFieldInspection */ $FLD_FLAGS = 4;
|
||
/** @var int Key to collection cache version number */
|
||
private static $FLD_VALUE_VERSION = 5;
|
||
/** @var int Key to how long it took to generate the value */
|
||
private static $FLD_GENERATION_TIME = 6;
|
||
|
||
private static $VALUE_KEY_PREFIX = 'WANCache:v:';
|
||
private static $INTERIM_KEY_PREFIX = 'WANCache:i:';
|
||
private static $TIME_KEY_PREFIX = 'WANCache:t:';
|
||
private static $MUTEX_KEY_PREFIX = 'WANCache:m:';
|
||
private static $COOLOFF_KEY_PREFIX = 'WANCache:c:';
|
||
|
||
private static $PURGE_VAL_PREFIX = 'PURGED:';
|
||
|
||
/**
|
||
* @param array $params
|
||
* - cache : BagOStuff object for a persistent cache
|
||
* - logger : LoggerInterface object
|
||
* - stats : StatsdDataFactoryInterface object
|
||
* - asyncHandler : A function that takes a callback and runs it later. If supplied,
|
||
* whenever a preemptive refresh would be triggered in getWithSetCallback(), the
|
||
* current cache value is still used instead. However, the async-handler function
|
||
* receives a WAN cache callback that, when run, will execute the value generation
|
||
* callback supplied by the getWithSetCallback() caller. The result will be saved
|
||
* as normal. The handler is expected to call the WAN cache callback at an opportune
|
||
* time (e.g. HTTP post-send), though generally within a few 100ms. [optional]
|
||
* - region: the current physical region. This is required when using mcrouter as the
|
||
* backing store proxy. [optional]
|
||
* - cluster: name of the cache cluster used by this WAN cache. The name must be the
|
||
* same in all datacenters; the ("region","cluster") tuple is what distinguishes
|
||
* the counterpart cache clusters among all the datacenter. The contents of
|
||
* https://github.com/facebook/mcrouter/wiki/Config-Files give background on this.
|
||
* This is required when using mcrouter as the backing store proxy. [optional]
|
||
* - mcrouterAware: set as true if mcrouter is the backing store proxy and mcrouter
|
||
* is configured to interpret /<region>/<cluster>/ key prefixes as routes. This
|
||
* requires that "region" and "cluster" are both set above. [optional]
|
||
* - epoch: lowest UNIX timestamp a value/tombstone must have to be valid. [optional]
|
||
* - secret: stable secret used for hashing long strings into key components. [optional]
|
||
*/
|
||
public function __construct( array $params ) {
|
||
$this->cache = $params['cache'];
|
||
$this->region = $params['region'] ?? 'main';
|
||
$this->cluster = $params['cluster'] ?? 'wan-main';
|
||
$this->mcrouterAware = !empty( $params['mcrouterAware'] );
|
||
$this->epoch = $params['epoch'] ?? 0;
|
||
$this->secret = $params['secret'] ?? (string)$this->epoch;
|
||
|
||
$this->setLogger( $params['logger'] ?? new NullLogger() );
|
||
$this->stats = $params['stats'] ?? new NullStatsdDataFactory();
|
||
$this->asyncHandler = $params['asyncHandler'] ?? null;
|
||
}
|
||
|
||
/**
|
||
* @param LoggerInterface $logger
|
||
*/
|
||
public function setLogger( LoggerInterface $logger ) {
|
||
$this->logger = $logger;
|
||
}
|
||
|
||
/**
|
||
* Get an instance that wraps EmptyBagOStuff
|
||
*
|
||
* @return WANObjectCache
|
||
*/
|
||
public static function newEmpty() {
|
||
return new static( [ 'cache' => new EmptyBagOStuff() ] );
|
||
}
|
||
|
||
/**
|
||
* Fetch the value of a key from cache
|
||
*
|
||
* If supplied, $curTTL is set to the remaining TTL (current time left):
|
||
* - a) INF; if $key exists, has no TTL, and is not invalidated by $checkKeys
|
||
* - b) float (>=0); if $key exists, has a TTL, and is not invalidated by $checkKeys
|
||
* - c) float (<0); if $key is tombstoned, stale, or existing but invalidated by $checkKeys
|
||
* - d) null; if $key does not exist and is not tombstoned
|
||
*
|
||
* If a key is tombstoned, $curTTL will reflect the time since delete().
|
||
*
|
||
* The timestamp of $key will be checked against the last-purge timestamp
|
||
* of each of $checkKeys. Those $checkKeys not in cache will have the last-purge
|
||
* initialized to the current timestamp. If any of $checkKeys have a timestamp
|
||
* greater than that of $key, then $curTTL will reflect how long ago $key
|
||
* became invalid. Callers can use $curTTL to know when the value is stale.
|
||
* The $checkKeys parameter allow mass invalidations by updating a single key:
|
||
* - a) Each "check" key represents "last purged" of some source data
|
||
* - b) Callers pass in relevant "check" keys as $checkKeys in get()
|
||
* - c) When the source data that "check" keys represent changes,
|
||
* the touchCheckKey() method is called on them
|
||
*
|
||
* Source data entities might exists in a DB that uses snapshot isolation
|
||
* (e.g. the default REPEATABLE-READ in innoDB). Even for mutable data, that
|
||
* isolation can largely be maintained by doing the following:
|
||
* - a) Calling delete() on entity change *and* creation, before DB commit
|
||
* - b) Keeping transaction duration shorter than the delete() hold-off TTL
|
||
* - c) Disabling interim key caching via useInterimHoldOffCaching() before get() calls
|
||
*
|
||
* However, pre-snapshot values might still be seen if an update was made
|
||
* in a remote datacenter but the purge from delete() didn't relay yet.
|
||
*
|
||
* Consider using getWithSetCallback() instead of get() and set() cycles.
|
||
* That method has cache slam avoiding features for hot/expensive keys.
|
||
*
|
||
* Pass $info as WANObjectCache::PASS_BY_REF to transform it into a cache key metadata map.
|
||
* This map includes the following metadata:
|
||
* - asOf: UNIX timestamp of the value or null if the key is nonexistant
|
||
* - tombAsOf: UNIX timestamp of the tombstone or null if the key is not tombstoned
|
||
* - lastCKPurge: UNIX timestamp of the highest check key or null if none provided
|
||
* - version: cached value version number or null if the key is nonexistant
|
||
*
|
||
* Otherwise, $info will transform into the cached value timestamp.
|
||
*
|
||
* @param string $key Cache key made from makeKey() or makeGlobalKey()
|
||
* @param mixed|null &$curTTL Approximate TTL left on the key if present/tombstoned [returned]
|
||
* @param string[] $checkKeys The "check" keys used to validate the value
|
||
* @param mixed|null &$info Key info if WANObjectCache::PASS_BY_REF [returned]
|
||
* @return mixed Value of cache key or false on failure
|
||
*/
|
||
final public function get(
|
||
$key, &$curTTL = null, array $checkKeys = [], &$info = null
|
||
) {
|
||
$curTTLs = self::PASS_BY_REF;
|
||
$infoByKey = self::PASS_BY_REF;
|
||
$values = $this->getMulti( [ $key ], $curTTLs, $checkKeys, $infoByKey );
|
||
$curTTL = $curTTLs[$key] ?? null;
|
||
if ( $info === self::PASS_BY_REF ) {
|
||
$info = [
|
||
'asOf' => $infoByKey[$key]['asOf'] ?? null,
|
||
'tombAsOf' => $infoByKey[$key]['tombAsOf'] ?? null,
|
||
'lastCKPurge' => $infoByKey[$key]['lastCKPurge'] ?? null,
|
||
'version' => $infoByKey[$key]['version'] ?? null
|
||
];
|
||
} else {
|
||
$info = $infoByKey[$key]['asOf'] ?? null; // b/c
|
||
}
|
||
|
||
return $values[$key] ?? false;
|
||
}
|
||
|
||
/**
|
||
* Fetch the value of several keys from cache
|
||
*
|
||
* Pass $info as WANObjectCache::PASS_BY_REF to transform it into a map of cache keys
|
||
* to cache key metadata maps, each having the same style as those of WANObjectCache::get().
|
||
* All the cache keys listed in $keys will have an entry.
|
||
*
|
||
* Othwerwise, $info will transform into a map of (cache key => cached value timestamp).
|
||
* Only the cache keys listed in $keys that exists or are tombstoned will have an entry.
|
||
*
|
||
* $checkKeys holds the "check" keys used to validate values of applicable keys. The integer
|
||
* indexes hold "check" keys that apply to all of $keys while the string indexes hold "check"
|
||
* keys that only apply to the cache key with that name.
|
||
*
|
||
* @see WANObjectCache::get()
|
||
*
|
||
* @param string[] $keys List of cache keys made from makeKey() or makeGlobalKey()
|
||
* @param mixed|null &$curTTLs Map of (key => TTL left) for existing/tombstoned keys [returned]
|
||
* @param string[]|string[][] $checkKeys Map of (integer or cache key => "check" key(s))
|
||
* @param mixed|null &$info Map of (key => info) if WANObjectCache::PASS_BY_REF [returned]
|
||
* @return mixed[] Map of (key => value) for existing values; order of $keys is preserved
|
||
*/
|
||
final public function getMulti(
|
||
array $keys,
|
||
&$curTTLs = [],
|
||
array $checkKeys = [],
|
||
&$info = null
|
||
) {
|
||
$result = [];
|
||
$curTTLs = [];
|
||
$infoByKey = [];
|
||
|
||
$vPrefixLen = strlen( self::$VALUE_KEY_PREFIX );
|
||
$valueKeys = self::prefixCacheKeys( $keys, self::$VALUE_KEY_PREFIX );
|
||
|
||
$checkKeysForAll = [];
|
||
$checkKeysByKey = [];
|
||
$checkKeysFlat = [];
|
||
foreach ( $checkKeys as $i => $checkKeyGroup ) {
|
||
$prefixed = self::prefixCacheKeys( (array)$checkKeyGroup, self::$TIME_KEY_PREFIX );
|
||
$checkKeysFlat = array_merge( $checkKeysFlat, $prefixed );
|
||
// Are these check keys for a specific cache key, or for all keys being fetched?
|
||
if ( is_int( $i ) ) {
|
||
$checkKeysForAll = array_merge( $checkKeysForAll, $prefixed );
|
||
} else {
|
||
$checkKeysByKey[$i] = $prefixed;
|
||
}
|
||
}
|
||
|
||
// Fetch all of the raw values
|
||
$keysGet = array_merge( $valueKeys, $checkKeysFlat );
|
||
if ( $this->warmupCache ) {
|
||
$wrappedValues = array_intersect_key( $this->warmupCache, array_flip( $keysGet ) );
|
||
$keysGet = array_diff( $keysGet, array_keys( $wrappedValues ) ); // keys left to fetch
|
||
$this->warmupKeyMisses += count( $keysGet );
|
||
} else {
|
||
$wrappedValues = [];
|
||
}
|
||
if ( $keysGet ) {
|
||
$wrappedValues += $this->cache->getMulti( $keysGet );
|
||
}
|
||
// Time used to compare/init "check" keys (derived after getMulti() to be pessimistic)
|
||
$now = $this->getCurrentTime();
|
||
|
||
// Collect timestamps from all "check" keys
|
||
$purgeValuesForAll = $this->processCheckKeys( $checkKeysForAll, $wrappedValues, $now );
|
||
$purgeValuesByKey = [];
|
||
foreach ( $checkKeysByKey as $cacheKey => $checks ) {
|
||
$purgeValuesByKey[$cacheKey] =
|
||
$this->processCheckKeys( $checks, $wrappedValues, $now );
|
||
}
|
||
|
||
// Get the main cache value for each key and validate them
|
||
foreach ( $valueKeys as $vKey ) {
|
||
$key = substr( $vKey, $vPrefixLen ); // unprefix
|
||
list( $value, $keyInfo ) = $this->unwrap( $wrappedValues[$vKey] ?? false, $now );
|
||
// Force dependent keys to be seen as stale for a while after purging
|
||
// to reduce race conditions involving stale data getting cached
|
||
$purgeValues = $purgeValuesForAll;
|
||
if ( isset( $purgeValuesByKey[$key] ) ) {
|
||
$purgeValues = array_merge( $purgeValues, $purgeValuesByKey[$key] );
|
||
}
|
||
|
||
$lastCKPurge = null; // timestamp of the highest check key
|
||
foreach ( $purgeValues as $purge ) {
|
||
$lastCKPurge = max( $purge[self::$PURGE_TIME], $lastCKPurge );
|
||
$safeTimestamp = $purge[self::$PURGE_TIME] + $purge[self::$PURGE_HOLDOFF];
|
||
if ( $value !== false && $safeTimestamp >= $keyInfo['asOf'] ) {
|
||
// How long ago this value was invalidated by *this* check key
|
||
$ago = min( $purge[self::$PURGE_TIME] - $now, self::$TINY_NEGATIVE );
|
||
// How long ago this value was invalidated by *any* known check key
|
||
$keyInfo['curTTL'] = min( $keyInfo['curTTL'], $ago );
|
||
}
|
||
}
|
||
$keyInfo[ 'lastCKPurge'] = $lastCKPurge;
|
||
|
||
if ( $value !== false ) {
|
||
$result[$key] = $value;
|
||
}
|
||
if ( $keyInfo['curTTL'] !== null ) {
|
||
$curTTLs[$key] = $keyInfo['curTTL'];
|
||
}
|
||
|
||
$infoByKey[$key] = ( $info === self::PASS_BY_REF )
|
||
? $keyInfo
|
||
: $keyInfo['asOf']; // b/c
|
||
}
|
||
|
||
$info = $infoByKey;
|
||
|
||
return $result;
|
||
}
|
||
|
||
/**
|
||
* @since 1.27
|
||
* @param string[] $timeKeys List of prefixed time check keys
|
||
* @param mixed[] $wrappedValues
|
||
* @param float $now
|
||
* @return array[] List of purge value arrays
|
||
*/
|
||
private function processCheckKeys( array $timeKeys, array $wrappedValues, $now ) {
|
||
$purgeValues = [];
|
||
foreach ( $timeKeys as $timeKey ) {
|
||
$purge = isset( $wrappedValues[$timeKey] )
|
||
? $this->parsePurgeValue( $wrappedValues[$timeKey] )
|
||
: false;
|
||
if ( $purge === false ) {
|
||
// Key is not set or malformed; regenerate
|
||
$newVal = $this->makePurgeValue( $now, self::HOLDOFF_TTL );
|
||
$this->cache->add( $timeKey, $newVal, self::$CHECK_KEY_TTL );
|
||
$purge = $this->parsePurgeValue( $newVal );
|
||
}
|
||
$purgeValues[] = $purge;
|
||
}
|
||
|
||
return $purgeValues;
|
||
}
|
||
|
||
/**
|
||
* Set the value of a key in cache
|
||
*
|
||
* Simply calling this method when source data changes is not valid because
|
||
* the changes do not replicate to the other WAN sites. In that case, delete()
|
||
* should be used instead. This method is intended for use on cache misses.
|
||
*
|
||
* If the data was read from a snapshot-isolated transactions (e.g. the default
|
||
* REPEATABLE-READ in innoDB), use 'since' to avoid the following race condition:
|
||
* - a) T1 starts
|
||
* - b) T2 updates a row, calls delete(), and commits
|
||
* - c) The HOLDOFF_TTL passes, expiring the delete() tombstone
|
||
* - d) T1 reads the row and calls set() due to a cache miss
|
||
* - e) Stale value is stuck in cache
|
||
*
|
||
* Setting 'lag' and 'since' help avoids keys getting stuck in stale states.
|
||
*
|
||
* Be aware that this does not update the process cache for getWithSetCallback()
|
||
* callers. Keys accessed via that method are not generally meant to also be set
|
||
* using this primitive method.
|
||
*
|
||
* Do not use this method on versioned keys accessed via getWithSetCallback().
|
||
*
|
||
* Example usage:
|
||
* @code
|
||
* $dbr = wfGetDB( DB_REPLICA );
|
||
* $setOpts = Database::getCacheSetOptions( $dbr );
|
||
* // Fetch the row from the DB
|
||
* $row = $dbr->selectRow( ... );
|
||
* $key = $cache->makeKey( 'building', $buildingId );
|
||
* $cache->set( $key, $row, $cache::TTL_DAY, $setOpts );
|
||
* @endcode
|
||
*
|
||
* @param string $key Cache key
|
||
* @param mixed $value
|
||
* @param int $ttl Seconds to live. Special values are:
|
||
* - WANObjectCache::TTL_INDEFINITE: Cache forever (default)
|
||
* - WANObjectCache::TTL_UNCACHEABLE: Do not cache (if the key exists, it is not deleted)
|
||
* @param array $opts Options map:
|
||
* - lag: Seconds of replica DB lag. Typically, this is either the replica DB lag
|
||
* before the data was read or, if applicable, the replica DB lag before
|
||
* the snapshot-isolated transaction the data was read from started.
|
||
* Use false to indicate that replication is not running.
|
||
* Default: 0 seconds
|
||
* - since: UNIX timestamp of the data in $value. Typically, this is either
|
||
* the current time the data was read or (if applicable) the time when
|
||
* the snapshot-isolated transaction the data was read from started.
|
||
* Default: 0 seconds
|
||
* - pending: Whether this data is possibly from an uncommitted write transaction.
|
||
* Generally, other threads should not see values from the future and
|
||
* they certainly should not see ones that ended up getting rolled back.
|
||
* Default: false
|
||
* - lockTSE: If excessive replication/snapshot lag is detected, then store the value
|
||
* with this TTL and flag it as stale. This is only useful if the reads for this key
|
||
* use getWithSetCallback() with "lockTSE" set. Note that if "staleTTL" is set
|
||
* then it will still add on to this TTL in the excessive lag scenario.
|
||
* Default: WANObjectCache::TSE_NONE
|
||
* - staleTTL: Seconds to keep the key around if it is stale. The get()/getMulti()
|
||
* methods return such stale values with a $curTTL of 0, and getWithSetCallback()
|
||
* will call the regeneration callback in such cases, passing in the old value
|
||
* and its as-of time to the callback. This is useful if adaptiveTTL() is used
|
||
* on the old value's as-of time when it is verified as still being correct.
|
||
* Default: WANObjectCache::STALE_TTL_NONE
|
||
* - creating: Optimize for the case where the key does not already exist.
|
||
* Default: false
|
||
* - version: Integer version number signifiying the format of the value.
|
||
* Default: null
|
||
* - walltime: How long the value took to generate in seconds. Default: 0.0
|
||
* @codingStandardsIgnoreStart
|
||
* @phan-param array{lag?:int,since?:int,pending?:bool,lockTSE?:int,staleTTL?:int,creating?:bool,version?:?string,walltime?:int|float} $opts
|
||
* @codingStandardsIgnoreEnd
|
||
* @note Options added in 1.28: staleTTL
|
||
* @note Options added in 1.33: creating
|
||
* @note Options added in 1.34: version, walltime
|
||
* @return bool Success
|
||
*/
|
||
final public function set( $key, $value, $ttl = self::TTL_INDEFINITE, array $opts = [] ) {
|
||
$now = $this->getCurrentTime();
|
||
$lag = $opts['lag'] ?? 0;
|
||
$age = isset( $opts['since'] ) ? max( 0, $now - $opts['since'] ) : 0;
|
||
$pending = $opts['pending'] ?? false;
|
||
$lockTSE = $opts['lockTSE'] ?? self::TSE_NONE;
|
||
$staleTTL = $opts['staleTTL'] ?? self::STALE_TTL_NONE;
|
||
$creating = $opts['creating'] ?? false;
|
||
$version = $opts['version'] ?? null;
|
||
$walltime = $opts['walltime'] ?? 0.0;
|
||
|
||
if ( $ttl < 0 ) {
|
||
return true;
|
||
}
|
||
|
||
// Do not cache potentially uncommitted data as it might get rolled back
|
||
if ( $pending ) {
|
||
$this->logger->info(
|
||
'Rejected set() for {cachekey} due to pending writes.',
|
||
[ 'cachekey' => $key ]
|
||
);
|
||
|
||
return true; // no-op the write for being unsafe
|
||
}
|
||
|
||
$logicalTTL = null; // logical TTL override
|
||
// Check if there's a risk of writing stale data after the purge tombstone expired
|
||
if ( $lag === false || ( $lag + $age ) > self::MAX_READ_LAG ) {
|
||
// Case A: any long-running transaction
|
||
if ( $age > self::MAX_READ_LAG ) {
|
||
if ( $lockTSE >= 0 ) {
|
||
// Store value as *almost* stale to avoid cache and mutex stampedes
|
||
$logicalTTL = self::TTL_SECOND;
|
||
$this->logger->info(
|
||
'Lowered set() TTL for {cachekey} due to snapshot lag.',
|
||
[ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ]
|
||
);
|
||
} else {
|
||
$this->logger->info(
|
||
'Rejected set() for {cachekey} due to snapshot lag.',
|
||
[ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ]
|
||
);
|
||
|
||
return true; // no-op the write for being unsafe
|
||
}
|
||
// Case B: high replication lag; lower TTL instead of ignoring all set()s
|
||
} elseif ( $lag === false || $lag > self::MAX_READ_LAG ) {
|
||
if ( $lockTSE >= 0 ) {
|
||
$logicalTTL = min( $ttl ?: INF, self::TTL_LAGGED );
|
||
} else {
|
||
$ttl = min( $ttl ?: INF, self::TTL_LAGGED );
|
||
}
|
||
$this->logger->warning(
|
||
'Lowered set() TTL for {cachekey} due to replication lag.',
|
||
[ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ]
|
||
);
|
||
// Case C: medium length request with medium replication lag
|
||
} elseif ( $lockTSE >= 0 ) {
|
||
// Store value as *almost* stale to avoid cache and mutex stampedes
|
||
$logicalTTL = self::TTL_SECOND;
|
||
$this->logger->info(
|
||
'Lowered set() TTL for {cachekey} due to high read lag.',
|
||
[ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ]
|
||
);
|
||
} else {
|
||
$this->logger->info(
|
||
'Rejected set() for {cachekey} due to high read lag.',
|
||
[ 'cachekey' => $key, 'lag' => $lag, 'age' => $age ]
|
||
);
|
||
|
||
return true; // no-op the write for being unsafe
|
||
}
|
||
}
|
||
|
||
// Wrap that value with time/TTL/version metadata
|
||
$wrapped = $this->wrap( $value, $logicalTTL ?: $ttl, $version, $now, $walltime );
|
||
$storeTTL = $ttl + $staleTTL;
|
||
|
||
if ( $creating ) {
|
||
$ok = $this->cache->add( self::$VALUE_KEY_PREFIX . $key, $wrapped, $storeTTL );
|
||
} else {
|
||
$ok = $this->cache->merge(
|
||
self::$VALUE_KEY_PREFIX . $key,
|
||
function ( $cache, $key, $cWrapped ) use ( $wrapped ) {
|
||
// A string value means that it is a tombstone; do nothing in that case
|
||
return ( is_string( $cWrapped ) ) ? false : $wrapped;
|
||
},
|
||
$storeTTL,
|
||
1 // 1 attempt
|
||
);
|
||
}
|
||
|
||
return $ok;
|
||
}
|
||
|
||
/**
|
||
* Purge a key from all datacenters
|
||
*
|
||
* This should only be called when the underlying data (being cached)
|
||
* changes in a significant way. This deletes the key and starts a hold-off
|
||
* period where the key cannot be written to for a few seconds (HOLDOFF_TTL).
|
||
* This is done to avoid the following race condition:
|
||
* - a) Some DB data changes and delete() is called on a corresponding key
|
||
* - b) A request refills the key with a stale value from a lagged DB
|
||
* - c) The stale value is stuck there until the key is expired/evicted
|
||
*
|
||
* This is implemented by storing a special "tombstone" value at the cache
|
||
* key that this class recognizes; get() calls will return false for the key
|
||
* and any set() calls will refuse to replace tombstone values at the key.
|
||
* For this to always avoid stale value writes, the following must hold:
|
||
* - a) Replication lag is bounded to being less than HOLDOFF_TTL; or
|
||
* - b) If lag is higher, the DB will have gone into read-only mode already
|
||
*
|
||
* Note that set() can also be lag-aware and lower the TTL if it's high.
|
||
*
|
||
* Be aware that this does not clear the process cache. Even if it did, callbacks
|
||
* used by getWithSetCallback() might still return stale data in the case of either
|
||
* uncommitted or not-yet-replicated changes (callback generally use replica DBs).
|
||
*
|
||
* When using potentially long-running ACID transactions, a good pattern is
|
||
* to use a pre-commit hook to issue the delete. This means that immediately
|
||
* after commit, callers will see the tombstone in cache upon purge relay.
|
||
* It also avoids the following race condition:
|
||
* - a) T1 begins, changes a row, and calls delete()
|
||
* - b) The HOLDOFF_TTL passes, expiring the delete() tombstone
|
||
* - c) T2 starts, reads the row and calls set() due to a cache miss
|
||
* - d) T1 finally commits
|
||
* - e) Stale value is stuck in cache
|
||
*
|
||
* Example usage:
|
||
* @code
|
||
* $dbw->startAtomic( __METHOD__ ); // start of request
|
||
* ... <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_TTL_NONE. Likewise for user-requested purge.
|
||
* Note that $ttl limits the effective range of 'lockTSE' for getWithSetCallback().
|
||
*
|
||
* If called twice on the same key, then the last hold-off TTL takes precedence. For
|
||
* idempotence, the $ttl should not vary for different delete() calls on the same key.
|
||
*
|
||
* @param string $key Cache key
|
||
* @param int $ttl Tombstone TTL; Default: WANObjectCache::HOLDOFF_TTL
|
||
* @return bool True if the item was purged or not found, false on failure
|
||
*/
|
||
final public function delete( $key, $ttl = self::HOLDOFF_TTL ) {
|
||
if ( $ttl <= 0 ) {
|
||
// Publish the purge to all datacenters
|
||
$ok = $this->relayDelete( self::$VALUE_KEY_PREFIX . $key );
|
||
} else {
|
||
// Publish the purge to all datacenters
|
||
$ok = $this->relayPurge( self::$VALUE_KEY_PREFIX . $key, $ttl, self::HOLDOFF_TTL_NONE );
|
||
}
|
||
|
||
$kClass = $this->determineKeyClassForStats( $key );
|
||
$this->stats->increment( "wanobjectcache.$kClass.delete." . ( $ok ? 'ok' : 'error' ) );
|
||
|
||
return $ok;
|
||
}
|
||
|
||
/**
|
||
* Fetch the value of a timestamp "check" key
|
||
*
|
||
* The key will be *initialized* to the current time if not set,
|
||
* so only call this method if this behavior is actually desired
|
||
*
|
||
* The timestamp can be used to check whether a cached value is valid.
|
||
* Callers should not assume that this returns the same timestamp in
|
||
* all datacenters due to relay delays.
|
||
*
|
||
* The level of staleness can roughly be estimated from this key, but
|
||
* if the key was evicted from cache, such calculations may show the
|
||
* time since expiry as ~0 seconds.
|
||
*
|
||
* Note that "check" keys won't collide with other regular keys.
|
||
*
|
||
* @param string $key
|
||
* @return float UNIX timestamp
|
||
*/
|
||
final public function getCheckKeyTime( $key ) {
|
||
return $this->getMultiCheckKeyTime( [ $key ] )[$key];
|
||
}
|
||
|
||
/**
|
||
* Fetch the values of each timestamp "check" key
|
||
*
|
||
* This works like getCheckKeyTime() except it takes a list of keys
|
||
* and returns a map of timestamps instead of just that of one key
|
||
*
|
||
* This might be useful if both:
|
||
* - a) a class of entities each depend on hundreds of other entities
|
||
* - b) these other entities are depended upon by millions of entities
|
||
*
|
||
* The later entities can each use a "check" key to invalidate their dependee entities.
|
||
* However, it is expensive for the former entities to verify against all of the relevant
|
||
* "check" keys during each getWithSetCallback() call. A less expensive approach is to do
|
||
* these verifications only after a "time-till-verify" (TTV) has passed. This is a middle
|
||
* ground between using blind TTLs and using constant verification. The adaptiveTTL() method
|
||
* can be used to dynamically adjust the TTV. Also, the initial TTV can make use of the
|
||
* last-modified times of the dependant entities (either from the DB or the "check" keys).
|
||
*
|
||
* Example usage:
|
||
* @code
|
||
* $value = $cache->getWithSetCallback(
|
||
* $cache->makeGlobalKey( 'wikibase-item', $id ),
|
||
* self::INITIAL_TTV, // initial time-till-verify
|
||
* function ( $oldValue, &$ttv, &$setOpts, $oldAsOf ) use ( $checkKeys, $cache ) {
|
||
* $now = microtime( true );
|
||
* // Use $oldValue if it passes max ultimate age and "check" key comparisons
|
||
* if ( $oldValue &&
|
||
* $oldAsOf > max( $cache->getMultiCheckKeyTime( $checkKeys ) ) &&
|
||
* ( $now - $oldValue['ctime'] ) <= self::MAX_CACHE_AGE
|
||
* ) {
|
||
* // Increase time-till-verify by 50% of last time to reduce overhead
|
||
* $ttv = $cache->adaptiveTTL( $oldAsOf, self::MAX_TTV, self::MIN_TTV, 1.5 );
|
||
* // Unlike $oldAsOf, "ctime" is the ultimate age of the cached data
|
||
* return $oldValue;
|
||
* }
|
||
*
|
||
* $mtimes = []; // dependency last-modified times; passed by reference
|
||
* $value = [ 'data' => $this->fetchEntityData( $mtimes ), 'ctime' => $now ];
|
||
* // Guess time-till-change among the dependencies, e.g. 1/(total change rate)
|
||
* $ttc = 1 / array_sum( array_map(
|
||
* function ( $mtime ) use ( $now ) {
|
||
* return 1 / ( $mtime ? ( $now - $mtime ) : 900 );
|
||
* },
|
||
* $mtimes
|
||
* ) );
|
||
* // The time-to-verify should not be overly pessimistic nor optimistic
|
||
* $ttv = min( max( $ttc, self::MIN_TTV ), self::MAX_TTV );
|
||
*
|
||
* return $value;
|
||
* },
|
||
* [ 'staleTTL' => $cache::TTL_DAY ] // keep around to verify and re-save
|
||
* );
|
||
* @endcode
|
||
*
|
||
* @see WANObjectCache::getCheckKeyTime()
|
||
* @see WANObjectCache::getWithSetCallback()
|
||
*
|
||
* @param string[] $keys
|
||
* @return float[] Map of (key => UNIX timestamp)
|
||
* @since 1.31
|
||
*/
|
||
final public function getMultiCheckKeyTime( array $keys ) {
|
||
$rawKeys = [];
|
||
foreach ( $keys as $key ) {
|
||
$rawKeys[$key] = self::$TIME_KEY_PREFIX . $key;
|
||
}
|
||
|
||
$rawValues = $this->cache->getMulti( $rawKeys );
|
||
$rawValues += array_fill_keys( $rawKeys, false );
|
||
|
||
$times = [];
|
||
foreach ( $rawKeys as $key => $rawKey ) {
|
||
$purge = $this->parsePurgeValue( $rawValues[$rawKey] );
|
||
if ( $purge !== false ) {
|
||
$time = $purge[self::$PURGE_TIME];
|
||
} else {
|
||
// Casting assures identical floats for the next getCheckKeyTime() calls
|
||
$now = (string)$this->getCurrentTime();
|
||
$this->cache->add(
|
||
$rawKey,
|
||
$this->makePurgeValue( $now, self::HOLDOFF_TTL ),
|
||
self::$CHECK_KEY_TTL
|
||
);
|
||
$time = (float)$now;
|
||
}
|
||
|
||
$times[$key] = $time;
|
||
}
|
||
|
||
return $times;
|
||
}
|
||
|
||
/**
|
||
* Purge a "check" key from all datacenters, invalidating keys that use it
|
||
*
|
||
* This should only be called when the underlying data (being cached)
|
||
* changes in a significant way, and it is impractical to call delete()
|
||
* on all keys that should be changed. When get() is called on those
|
||
* keys, the relevant "check" keys must be supplied for this to work.
|
||
*
|
||
* The "check" key essentially represents a last-modified time of an entity.
|
||
* When the key is touched, the timestamp will be updated to the current time.
|
||
* Keys using the "check" key via get(), getMulti(), or getWithSetCallback() will
|
||
* be invalidated. This approach is useful if many keys depend on a single entity.
|
||
*
|
||
* The timestamp of the "check" key is treated as being HOLDOFF_TTL seconds in the
|
||
* future by get*() methods in order to avoid race conditions where keys are updated
|
||
* with stale values (e.g. from a lagged replica DB). A high TTL is set on the "check"
|
||
* key, making it possible to know the timestamp of the last change to the corresponding
|
||
* entities in most cases. This might use more cache space than resetCheckKey().
|
||
*
|
||
* When a few important keys get a large number of hits, a high cache time is usually
|
||
* desired as well as "lockTSE" logic. The resetCheckKey() method is less appropriate
|
||
* in such cases since the "time since expiry" cannot be inferred, causing any get()
|
||
* after the reset to treat the key as being "hot", resulting in more stale value usage.
|
||
*
|
||
* Note that "check" keys won't collide with other regular keys.
|
||
*
|
||
* @see WANObjectCache::get()
|
||
* @see WANObjectCache::getWithSetCallback()
|
||
* @see WANObjectCache::resetCheckKey()
|
||
*
|
||
* @param string $key Cache key
|
||
* @param int $holdoff HOLDOFF_TTL or HOLDOFF_TTL_NONE constant
|
||
* @return bool True if the item was purged or not found, false on failure
|
||
*/
|
||
final public function touchCheckKey( $key, $holdoff = self::HOLDOFF_TTL ) {
|
||
// Publish the purge to all datacenters
|
||
$ok = $this->relayPurge( self::$TIME_KEY_PREFIX . $key, self::$CHECK_KEY_TTL, $holdoff );
|
||
|
||
$kClass = $this->determineKeyClassForStats( $key );
|
||
$this->stats->increment( "wanobjectcache.$kClass.ck_touch." . ( $ok ? 'ok' : 'error' ) );
|
||
|
||
return $ok;
|
||
}
|
||
|
||
/**
|
||
* Delete a "check" key from all datacenters, invalidating keys that use it
|
||
*
|
||
* This is similar to touchCheckKey() in that keys using it via get(), getMulti(),
|
||
* or getWithSetCallback() will be invalidated. The differences are:
|
||
* - a) The "check" key will be deleted from all caches and lazily
|
||
* re-initialized when accessed (rather than set everywhere)
|
||
* - b) Thus, dependent keys will be known to be stale, but not
|
||
* for how long (they are treated as "just" purged), which
|
||
* effects any lockTSE logic in getWithSetCallback()
|
||
* - c) Since "check" keys are initialized only on the server the key hashes
|
||
* to, any temporary ejection of that server will cause the value to be
|
||
* seen as purged as a new server will initialize the "check" key.
|
||
*
|
||
* The advantage here is that the "check" keys, which have high TTLs, will only
|
||
* be created when a get*() method actually uses that key. This is better when
|
||
* a large number of "check" keys are invalided in a short period of time.
|
||
*
|
||
* Note that "check" keys won't collide with other regular keys.
|
||
*
|
||
* @see WANObjectCache::get()
|
||
* @see WANObjectCache::getWithSetCallback()
|
||
* @see WANObjectCache::touchCheckKey()
|
||
*
|
||
* @param string $key Cache key
|
||
* @return bool True if the item was purged or not found, false on failure
|
||
*/
|
||
final public function resetCheckKey( $key ) {
|
||
// Publish the purge to all datacenters
|
||
$ok = $this->relayDelete( self::$TIME_KEY_PREFIX . $key );
|
||
|
||
$kClass = $this->determineKeyClassForStats( $key );
|
||
$this->stats->increment( "wanobjectcache.$kClass.ck_reset." . ( $ok ? 'ok' : 'error' ) );
|
||
|
||
return $ok;
|
||
}
|
||
|
||
/**
|
||
* Method to fetch/regenerate cache keys
|
||
*
|
||
* On cache miss, the key will be set to the callback result via set()
|
||
* (unless the callback returns false) and that result will be returned.
|
||
* The arguments supplied to the callback are:
|
||
* - $oldValue : current cache value or false if not present
|
||
* - &$ttl : a reference to the TTL which can be altered
|
||
* - &$setOpts : a reference to options for set() which can be altered
|
||
* - $oldAsOf : generation UNIX timestamp of $oldValue or null if not present (since 1.28)
|
||
*
|
||
* It is strongly recommended to set the 'lag' and 'since' fields to avoid race conditions
|
||
* that can cause stale values to get stuck at keys. Usually, callbacks ignore the current
|
||
* value, but it can be used to maintain "most recent X" values that come from time or
|
||
* sequence based source data, provided that the "as of" id/time is tracked. Note that
|
||
* preemptive regeneration and $checkKeys can result in a non-false current value.
|
||
*
|
||
* Usage of $checkKeys is similar to get() and getMulti(). However, rather than the caller
|
||
* having to inspect a "current time left" variable (e.g. $curTTL, $curTTLs), a cache
|
||
* regeneration will automatically be triggered using the callback.
|
||
*
|
||
* The $ttl argument and "hotTTR" option (in $opts) use time-dependant randomization
|
||
* to avoid stampedes. Keys that are slow to regenerate and either heavily used
|
||
* or subject to explicit (unpredictable) purges, may need additional mechanisms.
|
||
* The simplest way to avoid stampedes for such keys is to use 'lockTSE' (in $opts).
|
||
* If explicit purges are needed, also:
|
||
* - a) Pass $key into $checkKeys
|
||
* - b) Use touchCheckKey( $key ) instead of delete( $key )
|
||
*
|
||
* Example usage (typical key):
|
||
* @code
|
||
* $catInfo = $cache->getWithSetCallback(
|
||
* // Key to store the cached value under
|
||
* $cache->makeKey( 'cat-attributes', $catId ),
|
||
* // Time-to-live (in seconds)
|
||
* $cache::TTL_MINUTE,
|
||
* // Function that derives the new key value
|
||
* function ( $oldValue, &$ttl, array &$setOpts ) {
|
||
* $dbr = wfGetDB( DB_REPLICA );
|
||
* // Account for any snapshot/replica DB lag
|
||
* $setOpts += Database::getCacheSetOptions( $dbr );
|
||
*
|
||
* return $dbr->selectRow( ... );
|
||
* }
|
||
* );
|
||
* @endcode
|
||
*
|
||
* Example usage (key that is expensive and hot):
|
||
* @code
|
||
* $catConfig = $cache->getWithSetCallback(
|
||
* // Key to store the cached value under
|
||
* $cache->makeKey( 'site-cat-config' ),
|
||
* // Time-to-live (in seconds)
|
||
* $cache::TTL_DAY,
|
||
* // Function that derives the new key value
|
||
* function ( $oldValue, &$ttl, array &$setOpts ) {
|
||
* $dbr = wfGetDB( DB_REPLICA );
|
||
* // Account for any snapshot/replica DB lag
|
||
* $setOpts += Database::getCacheSetOptions( $dbr );
|
||
*
|
||
* return CatConfig::newFromRow( $dbr->selectRow( ... ) );
|
||
* },
|
||
* [
|
||
* // Calling touchCheckKey() on this key invalidates the cache
|
||
* 'checkKeys' => [ $cache->makeKey( 'site-cat-config' ) ],
|
||
* // Try to only let one datacenter thread manage cache updates at a time
|
||
* 'lockTSE' => 30,
|
||
* // Avoid querying cache servers multiple times in a web request
|
||
* 'pcTTL' => $cache::TTL_PROC_LONG
|
||
* ]
|
||
* );
|
||
* @endcode
|
||
*
|
||
* Example usage (key with dynamic dependencies):
|
||
* @code
|
||
* $catState = $cache->getWithSetCallback(
|
||
* // Key to store the cached value under
|
||
* $cache->makeKey( 'cat-state', $cat->getId() ),
|
||
* // Time-to-live (seconds)
|
||
* $cache::TTL_HOUR,
|
||
* // Function that derives the new key value
|
||
* function ( $oldValue, &$ttl, array &$setOpts ) {
|
||
* // Determine new value from the DB
|
||
* $dbr = wfGetDB( DB_REPLICA );
|
||
* // Account for any snapshot/replica DB lag
|
||
* $setOpts += Database::getCacheSetOptions( $dbr );
|
||
*
|
||
* return CatState::newFromResults( $dbr->select( ... ) );
|
||
* },
|
||
* [
|
||
* // The "check" keys that represent things the value depends on;
|
||
* // Calling touchCheckKey() on any of them invalidates the cache
|
||
* 'checkKeys' => [
|
||
* $cache->makeKey( 'sustenance-bowls', $cat->getRoomId() ),
|
||
* $cache->makeKey( 'people-present', $cat->getHouseId() ),
|
||
* $cache->makeKey( 'cat-laws', $cat->getCityId() ),
|
||
* ]
|
||
* ]
|
||
* );
|
||
* @endcode
|
||
*
|
||
* Example usage (key that is expensive with too many DB dependencies for "check keys"):
|
||
* @code
|
||
* $catToys = $cache->getWithSetCallback(
|
||
* // Key to store the cached value under
|
||
* $cache->makeKey( 'cat-toys', $catId ),
|
||
* // Time-to-live (seconds)
|
||
* $cache::TTL_HOUR,
|
||
* // Function that derives the new key value
|
||
* function ( $oldValue, &$ttl, array &$setOpts ) {
|
||
* // Determine new value from the DB
|
||
* $dbr = wfGetDB( DB_REPLICA );
|
||
* // Account for any snapshot/replica DB lag
|
||
* $setOpts += Database::getCacheSetOptions( $dbr );
|
||
*
|
||
* return CatToys::newFromResults( $dbr->select( ... ) );
|
||
* },
|
||
* [
|
||
* // Get the highest timestamp of any of the cat's toys
|
||
* 'touchedCallback' => function ( $value ) use ( $catId ) {
|
||
* $dbr = wfGetDB( DB_REPLICA );
|
||
* $ts = $dbr->selectField( 'cat_toys', 'MAX(ct_touched)', ... );
|
||
*
|
||
* return wfTimestampOrNull( TS_UNIX, $ts );
|
||
* },
|
||
* // Avoid DB queries for repeated access
|
||
* 'pcTTL' => $cache::TTL_PROC_SHORT
|
||
* ]
|
||
* );
|
||
* @endcode
|
||
*
|
||
* Example usage (hot key holding most recent 100 events):
|
||
* @code
|
||
* $lastCatActions = $cache->getWithSetCallback(
|
||
* // Key to store the cached value under
|
||
* $cache->makeKey( 'cat-last-actions', 100 ),
|
||
* // Time-to-live (in seconds)
|
||
* 10,
|
||
* // Function that derives the new key value
|
||
* function ( $oldValue, &$ttl, array &$setOpts ) {
|
||
* $dbr = wfGetDB( DB_REPLICA );
|
||
* // Account for any snapshot/replica DB lag
|
||
* $setOpts += Database::getCacheSetOptions( $dbr );
|
||
*
|
||
* // Start off with the last cached list
|
||
* $list = $oldValue ?: [];
|
||
* // Fetch the last 100 relevant rows in descending order;
|
||
* // only fetch rows newer than $list[0] to reduce scanning
|
||
* $rows = iterator_to_array( $dbr->select( ... ) );
|
||
* // Merge them and get the new "last 100" rows
|
||
* return array_slice( array_merge( $new, $list ), 0, 100 );
|
||
* },
|
||
* [
|
||
* // Try to only let one datacenter thread manage cache updates at a time
|
||
* 'lockTSE' => 30,
|
||
* // Use a magic value when no cache value is ready rather than stampeding
|
||
* 'busyValue' => 'computing'
|
||
* ]
|
||
* );
|
||
* @endcode
|
||
*
|
||
* Example usage (key holding an LRU subkey:value map; this can avoid flooding cache with
|
||
* keys for an unlimited set of (constraint,situation) pairs, thereby avoiding elevated
|
||
* cache evictions and wasted memory):
|
||
* @code
|
||
* $catSituationTolerabilityCache = $this->cache->getWithSetCallback(
|
||
* // Group by constraint ID/hash, cat family ID/hash, or something else useful
|
||
* $this->cache->makeKey( 'cat-situation-tolerability-checks', $groupKey ),
|
||
* WANObjectCache::TTL_DAY, // rarely used groups should fade away
|
||
* // The $scenarioKey format is $constraintId:<ID/hash of $situation>
|
||
* function ( $cacheMap ) use ( $scenarioKey, $constraintId, $situation ) {
|
||
* $lruCache = MapCacheLRU::newFromArray( $cacheMap ?: [], self::CACHE_SIZE );
|
||
* $result = $lruCache->get( $scenarioKey ); // triggers LRU bump if present
|
||
* if ( $result === null || $this->isScenarioResultExpired( $result ) ) {
|
||
* $result = $this->checkScenarioTolerability( $constraintId, $situation );
|
||
* $lruCache->set( $scenarioKey, $result, 3 / 8 );
|
||
* }
|
||
* // Save the new LRU cache map and reset the map's TTL
|
||
* return $lruCache->toArray();
|
||
* },
|
||
* [
|
||
* // Once map is > 1 sec old, consider refreshing
|
||
* 'ageNew' => 1,
|
||
* // Update within 5 seconds after "ageNew" given a 1hz cache check rate
|
||
* 'hotTTR' => 5,
|
||
* // Avoid querying cache servers multiple times in a request; this also means
|
||
* // that a request can only alter the value of any given constraint key once
|
||
* 'pcTTL' => WANObjectCache::TTL_PROC_LONG
|
||
* ]
|
||
* );
|
||
* $tolerability = isset( $catSituationTolerabilityCache[$scenarioKey] )
|
||
* ? $catSituationTolerabilityCache[$scenarioKey]
|
||
* : $this->checkScenarioTolerability( $constraintId, $situation );
|
||
* @endcode
|
||
*
|
||
* @see WANObjectCache::get()
|
||
* @see WANObjectCache::set()
|
||
*
|
||
* @param string $key Cache key made from makeKey() or makeGlobalKey()
|
||
* @param int $ttl Seconds to live for key updates. Special values are:
|
||
* - WANObjectCache::TTL_INDEFINITE: Cache forever (subject to LRU-style evictions)
|
||
* - WANObjectCache::TTL_UNCACHEABLE: Do not cache (if the key exists, it is not deleted)
|
||
* @param callable $callback Value generation function
|
||
* @param array $opts Options map:
|
||
* - checkKeys: List of "check" keys. The key at $key will be seen as stale when either
|
||
* touchCheckKey() or resetCheckKey() is called on any of the keys in this list. This
|
||
* is useful if thousands or millions of keys depend on the same entity. The entity can
|
||
* simply have its "check" key updated whenever the entity is modified.
|
||
* Default: [].
|
||
* - graceTTL: If the key is invalidated (by "checkKeys"/"touchedCallback") less than this
|
||
* many seconds ago, consider reusing the stale value. The odds of a refresh becomes
|
||
* more likely over time, becoming certain once the grace period is reached. This can
|
||
* reduce traffic spikes when millions of keys are compared to the same "check" key and
|
||
* touchCheckKey() or resetCheckKey() is called on that "check" key. This option is not
|
||
* useful for avoiding traffic spikes in the case of the key simply expiring on account
|
||
* of its TTL (use "lowTTL" instead).
|
||
* Default: WANObjectCache::GRACE_TTL_NONE.
|
||
* - lockTSE: If the key is tombstoned or invalidated (by "checkKeys"/"touchedCallback")
|
||
* less than this many seconds ago, try to have a single thread handle cache regeneration
|
||
* at any given time. Other threads will use stale values if possible. If, on miss,
|
||
* the time since expiration is low, the assumption is that the key is hot and that a
|
||
* stampede is worth avoiding. Note that if the key falls out of cache then concurrent
|
||
* threads will all run the callback on cache miss until the value is saved in cache.
|
||
* The only stampede protection in that case is from duplicate cache sets when the
|
||
* callback takes longer than WANObjectCache::SET_DELAY_HIGH_MS milliseconds; consider
|
||
* using "busyValue" if such stampedes are a problem. Note that the higher "lockTSE" is
|
||
* set, the higher the worst-case staleness of returned values can be. Also note that
|
||
* this option does not by itself handle the case of the key simply expiring on account
|
||
* of its TTL, so make sure that "lowTTL" is not disabled when using this option. Avoid
|
||
* combining this option with delete() as it can always cause a stampede due to their
|
||
* being no stale value available until after a thread completes the callback.
|
||
* Use WANObjectCache::TSE_NONE to disable this logic.
|
||
* Default: WANObjectCache::TSE_NONE.
|
||
* - busyValue: Specify a placeholder value to use when no value exists and another thread
|
||
* is currently regenerating it. This assures that cache stampedes cannot happen if the
|
||
* value falls out of cache. This also mitigates stampedes when value regeneration
|
||
* becomes very slow (greater than $ttl/"lowTTL"). If this is a closure, then it will
|
||
* be invoked to get the placeholder when needed.
|
||
* Default: null.
|
||
* - pcTTL: Process cache the value in this PHP instance for this many seconds. This avoids
|
||
* network I/O when a key is read several times. This will not cache when the callback
|
||
* returns false, however. Note that any purges will not be seen while process cached;
|
||
* since the callback should use replica DBs and they may be lagged or have snapshot
|
||
* isolation anyway, this should not typically matter.
|
||
* Default: WANObjectCache::TTL_UNCACHEABLE.
|
||
* - pcGroup: Process cache group to use instead of the primary one. If set, this must be
|
||
* of the format ALPHANUMERIC_NAME:MAX_KEY_SIZE, e.g. "mydata:10". Use this for storing
|
||
* large values, small yet numerous values, or some values with a high cost of eviction.
|
||
* It is generally preferable to use a class constant when setting this value.
|
||
* This has no effect unless pcTTL is used.
|
||
* Default: WANObjectCache::PC_PRIMARY.
|
||
* - version: Integer version number. This lets callers make breaking changes to the format
|
||
* of cached values without causing problems for sites that use non-instantaneous code
|
||
* deployments. Old and new code will recognize incompatible versions and purges from
|
||
* both old and new code will been seen by each other. When this method encounters an
|
||
* incompatibly versioned value at the provided key, a "variant key" will be used for
|
||
* reading from and saving to cache. The variant key is specific to the key and version
|
||
* number provided to this method. If the variant key value is older than that of the
|
||
* provided key, or the provided key is non-existant, then the variant key will be seen
|
||
* as non-existant. Therefore, delete() calls invalidate the provided key's variant keys.
|
||
* The "checkKeys" and "touchedCallback" options still apply to variant keys as usual.
|
||
* Avoid storing class objects, as this reduces compatibility (due to serialization).
|
||
* Default: null.
|
||
* - minAsOf: Reject values if they were generated before this UNIX timestamp.
|
||
* This is useful if the source of a key is suspected of having possibly changed
|
||
* recently, and the caller wants any such changes to be reflected.
|
||
* Default: WANObjectCache::MIN_TIMESTAMP_NONE.
|
||
* - hotTTR: Expected time-till-refresh (TTR) in seconds for keys that average ~1 hit per
|
||
* second (e.g. 1Hz). Keys with a hit rate higher than 1Hz will refresh sooner than this
|
||
* TTR and vise versa. Such refreshes won't happen until keys are "ageNew" seconds old.
|
||
* This uses randomization to avoid triggering cache stampedes. The TTR is useful at
|
||
* reducing the impact of missed cache purges, since the effect of a heavily referenced
|
||
* key being stale is worse than that of a rarely referenced key. Unlike simply lowering
|
||
* $ttl, seldomly used keys are largely unaffected by this option, which makes it
|
||
* possible to have a high hit rate for the "long-tail" of less-used keys.
|
||
* Default: WANObjectCache::HOT_TTR.
|
||
* - lowTTL: Consider pre-emptive updates when the current TTL (seconds) of the key is less
|
||
* than this. It becomes more likely over time, becoming certain once the key is expired.
|
||
* This helps avoid cache stampedes that might be triggered due to the key expiring.
|
||
* Default: WANObjectCache::LOW_TTL.
|
||
* - ageNew: Consider popularity refreshes only once a key reaches this age in seconds.
|
||
* Default: WANObjectCache::AGE_NEW.
|
||
* - staleTTL: Seconds to keep the key around if it is stale. This means that on cache
|
||
* miss the callback may get $oldValue/$oldAsOf values for keys that have already been
|
||
* expired for this specified time. This is useful if adaptiveTTL() is used on the old
|
||
* value's as-of time when it is verified as still being correct.
|
||
* Default: WANObjectCache::STALE_TTL_NONE
|
||
* - touchedCallback: A callback that takes the current value and returns a UNIX timestamp
|
||
* indicating the last time a dynamic dependency changed. Null can be returned if there
|
||
* are no relevant dependency changes to check. This can be used to check against things
|
||
* like last-modified times of files or DB timestamp fields. This should generally not be
|
||
* used for small and easily queried values in a DB if the callback itself ends up doing
|
||
* a similarly expensive DB query to check a timestamp. Usages of this option makes the
|
||
* most sense for values that are moderately to highly expensive to regenerate and easy
|
||
* to query for dependency timestamps. The use of "pcTTL" reduces timestamp queries.
|
||
* Default: null.
|
||
* @codingStandardsIgnoreStart
|
||
* @phan-param array{checkKeys?:string[],graceTTL?:int,lockTSE?:int,busyValue?:mixed,pcTTL?:int,pcGroup?:string,version?:int,minAsOf?:int,hotTTR?:int,lowTTL?:int,ageNew?:int,staleTTL?:int,touchedCallback?:callable} $opts
|
||
* @codingStandardsIgnoreEnd
|
||
* @return mixed Value found or written to the key
|
||
* @note Options added in 1.28: version, busyValue, hotTTR, ageNew, pcGroup, minAsOf
|
||
* @note Options added in 1.31: staleTTL, graceTTL
|
||
* @note Options added in 1.33: touchedCallback
|
||
* @note Callable type hints are not used to avoid class-autoloading
|
||
*/
|
||
final public function getWithSetCallback( $key, $ttl, $callback, array $opts = [] ) {
|
||
$version = $opts['version'] ?? null;
|
||
$pcTTL = $opts['pcTTL'] ?? self::TTL_UNCACHEABLE;
|
||
$pCache = ( $pcTTL >= 0 )
|
||
? $this->getProcessCache( $opts['pcGroup'] ?? self::PC_PRIMARY )
|
||
: null;
|
||
|
||
// Use the process cache if requested as long as no outer cache callback is running.
|
||
// Nested callback process cache use is not lag-safe with regard to HOLDOFF_TTL since
|
||
// process cached values are more lagged than persistent ones as they are not purged.
|
||
if ( $pCache && $this->callbackDepth == 0 ) {
|
||
$cached = $pCache->get( $this->getProcessCacheKey( $key, $version ), $pcTTL, false );
|
||
if ( $cached !== false ) {
|
||
return $cached;
|
||
}
|
||
}
|
||
|
||
$res = $this->fetchOrRegenerate( $key, $ttl, $callback, $opts );
|
||
list( $value, $valueVersion, $curAsOf ) = $res;
|
||
if ( $valueVersion !== $version ) {
|
||
// Current value has a different version; use the variant key for this version.
|
||
// Regenerate the variant value if it is not newer than the main value at $key
|
||
// so that purges to the main key propagate to the variant value.
|
||
list( $value ) = $this->fetchOrRegenerate(
|
||
$this->makeGlobalKey( 'WANCache-key-variant', md5( $key ), $version ),
|
||
$ttl,
|
||
$callback,
|
||
[ 'version' => null, 'minAsOf' => $curAsOf ] + $opts
|
||
);
|
||
}
|
||
|
||
// Update the process cache if enabled
|
||
if ( $pCache && $value !== false ) {
|
||
$pCache->set( $this->getProcessCacheKey( $key, $version ), $value );
|
||
}
|
||
|
||
return $value;
|
||
}
|
||
|
||
/**
|
||
* Do the actual I/O for getWithSetCallback() when needed
|
||
*
|
||
* @see WANObjectCache::getWithSetCallback()
|
||
*
|
||
* @param string $key
|
||
* @param int $ttl
|
||
* @param callable $callback
|
||
* @param array $opts Options map for getWithSetCallback()
|
||
* @return array Ordered list of the following:
|
||
* - Cached or regenerated value
|
||
* - Cached or regenerated value version number or null if not versioned
|
||
* - Timestamp of the current cached value at the key or null if there is no value
|
||
* @note Callable type hints are not used to avoid class-autoloading
|
||
* @suppress PhanTypeArraySuspicious
|
||
*/
|
||
private function fetchOrRegenerate( $key, $ttl, $callback, array $opts ) {
|
||
$checkKeys = $opts['checkKeys'] ?? [];
|
||
$graceTTL = $opts['graceTTL'] ?? self::GRACE_TTL_NONE;
|
||
$minAsOf = $opts['minAsOf'] ?? self::MIN_TIMESTAMP_NONE;
|
||
$hotTTR = $opts['hotTTR'] ?? self::HOT_TTR;
|
||
$lowTTL = $opts['lowTTL'] ?? min( self::LOW_TTL, $ttl );
|
||
$ageNew = $opts['ageNew'] ?? self::AGE_NEW;
|
||
$touchedCb = $opts['touchedCallback'] ?? null;
|
||
$initialTime = $this->getCurrentTime();
|
||
|
||
$kClass = $this->determineKeyClassForStats( $key );
|
||
|
||
// Get the current key value and its metadata
|
||
$curTTL = self::PASS_BY_REF;
|
||
$curInfo = self::PASS_BY_REF;
|
||
$curValue = $this->get( $key, $curTTL, $checkKeys, $curInfo );
|
||
/** @var array $curInfo */
|
||
'@phan-var array $curInfo';
|
||
// Apply any $touchedCb invalidation timestamp to get the "last purge timestamp"
|
||
list( $curTTL, $LPT ) = $this->resolveCTL( $curValue, $curTTL, $curInfo, $touchedCb );
|
||
// Use the cached value if it exists and is not due for synchronous regeneration
|
||
if (
|
||
$this->isValid( $curValue, $curInfo['asOf'], $minAsOf ) &&
|
||
$this->isAliveOrInGracePeriod( $curTTL, $graceTTL )
|
||
) {
|
||
$preemptiveRefresh = (
|
||
$this->worthRefreshExpiring( $curTTL, $lowTTL ) ||
|
||
$this->worthRefreshPopular( $curInfo['asOf'], $ageNew, $hotTTR, $initialTime )
|
||
);
|
||
if ( !$preemptiveRefresh ) {
|
||
$this->stats->increment( "wanobjectcache.$kClass.hit.good" );
|
||
|
||
return [ $curValue, $curInfo['version'], $curInfo['asOf'] ];
|
||
} elseif ( $this->scheduleAsyncRefresh( $key, $ttl, $callback, $opts ) ) {
|
||
$this->stats->increment( "wanobjectcache.$kClass.hit.refresh" );
|
||
|
||
return [ $curValue, $curInfo['version'], $curInfo['asOf'] ];
|
||
}
|
||
}
|
||
|
||
// Determine if there is stale or volatile cached value that is still usable
|
||
$isKeyTombstoned = ( $curInfo['tombAsOf'] !== null );
|
||
if ( $isKeyTombstoned ) {
|
||
// Key is write-holed; use the (volatile) interim key as an alternative
|
||
list( $possValue, $possInfo ) = $this->getInterimValue( $key, $minAsOf );
|
||
// Update the "last purge time" since the $touchedCb timestamp depends on $value
|
||
$LPT = $this->resolveTouched( $possValue, $LPT, $touchedCb );
|
||
} else {
|
||
$possValue = $curValue;
|
||
$possInfo = $curInfo;
|
||
}
|
||
|
||
// Avoid overhead from callback runs, regeneration locks, and cache sets during
|
||
// hold-off periods for the key by reusing very recently generated cached values
|
||
if (
|
||
$this->isValid( $possValue, $possInfo['asOf'], $minAsOf, $LPT ) &&
|
||
$this->isVolatileValueAgeNegligible( $initialTime - $possInfo['asOf'] )
|
||
) {
|
||
$this->stats->increment( "wanobjectcache.$kClass.hit.volatile" );
|
||
|
||
return [ $possValue, $possInfo['version'], $curInfo['asOf'] ];
|
||
}
|
||
|
||
$lockTSE = $opts['lockTSE'] ?? self::TSE_NONE;
|
||
$busyValue = $opts['busyValue'] ?? null;
|
||
$staleTTL = $opts['staleTTL'] ?? self::STALE_TTL_NONE;
|
||
$version = $opts['version'] ?? null;
|
||
|
||
// Determine whether one thread per datacenter should handle regeneration at a time
|
||
$useRegenerationLock =
|
||
// Note that since tombstones no-op set(), $lockTSE and $curTTL cannot be used to
|
||
// deduce the key hotness because |$curTTL| will always keep increasing until the
|
||
// tombstone expires or is overwritten by a new tombstone. Also, even if $lockTSE
|
||
// is not set, constant regeneration of a key for the tombstone lifetime might be
|
||
// very expensive. Assume tombstoned keys are possibly hot in order to reduce
|
||
// the risk of high regeneration load after the delete() method is called.
|
||
$isKeyTombstoned ||
|
||
// Assume a key is hot if requested soon ($lockTSE seconds) after invalidation.
|
||
// This avoids stampedes when timestamps from $checkKeys/$touchedCb bump.
|
||
( $curTTL !== null && $curTTL <= 0 && abs( $curTTL ) <= $lockTSE ) ||
|
||
// Assume a key is hot if there is no value and a busy fallback is given.
|
||
// This avoids stampedes on eviction or preemptive regeneration taking too long.
|
||
( $busyValue !== null && $possValue === false );
|
||
|
||
// If a regeneration lock is required, threads that do not get the lock will try to use
|
||
// the stale value, the interim value, or the $busyValue placeholder, in that order. If
|
||
// none of those are set then all threads will bypass the lock and regenerate the value.
|
||
$hasLock = $useRegenerationLock && $this->claimStampedeLock( $key );
|
||
if ( $useRegenerationLock && !$hasLock ) {
|
||
if ( $this->isValid( $possValue, $possInfo['asOf'], $minAsOf ) ) {
|
||
$this->stats->increment( "wanobjectcache.$kClass.hit.stale" );
|
||
|
||
return [ $possValue, $possInfo['version'], $curInfo['asOf'] ];
|
||
} elseif ( $busyValue !== null ) {
|
||
$miss = is_infinite( $minAsOf ) ? 'renew' : 'miss';
|
||
$this->stats->increment( "wanobjectcache.$kClass.$miss.busy" );
|
||
|
||
return [ $this->resolveBusyValue( $busyValue ), $version, $curInfo['asOf'] ];
|
||
}
|
||
}
|
||
|
||
// Generate the new value given any prior value with a matching version
|
||
$setOpts = [];
|
||
$preCallbackTime = $this->getCurrentTime();
|
||
++$this->callbackDepth;
|
||
try {
|
||
$value = $callback(
|
||
( $curInfo['version'] === $version ) ? $curValue : false,
|
||
$ttl,
|
||
$setOpts,
|
||
( $curInfo['version'] === $version ) ? $curInfo['asOf'] : null
|
||
);
|
||
} finally {
|
||
--$this->callbackDepth;
|
||
}
|
||
$postCallbackTime = $this->getCurrentTime();
|
||
|
||
// How long it took to fetch, validate, and generate the value
|
||
$elapsed = max( $postCallbackTime - $initialTime, 0.0 );
|
||
|
||
// Attempt to save the newly generated value if applicable
|
||
if (
|
||
// Callback yielded a cacheable value
|
||
( $value !== false && $ttl >= 0 ) &&
|
||
// Current thread was not raced out of a regeneration lock or key is tombstoned
|
||
( !$useRegenerationLock || $hasLock || $isKeyTombstoned ) &&
|
||
// Key does not appear to be undergoing a set() stampede
|
||
$this->checkAndSetCooloff( $key, $kClass, $elapsed, $lockTSE, $hasLock )
|
||
) {
|
||
// How long it took to generate the value
|
||
$walltime = max( $postCallbackTime - $preCallbackTime, 0.0 );
|
||
$this->stats->timing( "wanobjectcache.$kClass.regen_walltime", 1e3 * $walltime );
|
||
// If the key is write-holed then use the (volatile) interim key as an alternative
|
||
if ( $isKeyTombstoned ) {
|
||
$this->setInterimValue( $key, $value, $lockTSE, $version, $walltime );
|
||
} else {
|
||
$finalSetOpts = [
|
||
'since' => $setOpts['since'] ?? $preCallbackTime,
|
||
'version' => $version,
|
||
'staleTTL' => $staleTTL,
|
||
'lockTSE' => $lockTSE, // informs lag vs performance trade-offs
|
||
'creating' => ( $curValue === false ), // optimization
|
||
'walltime' => $walltime
|
||
] + $setOpts;
|
||
$this->set( $key, $value, $ttl, $finalSetOpts );
|
||
}
|
||
}
|
||
|
||
$this->yieldStampedeLock( $key, $hasLock );
|
||
|
||
$miss = is_infinite( $minAsOf ) ? 'renew' : 'miss';
|
||
$this->stats->increment( "wanobjectcache.$kClass.$miss.compute" );
|
||
|
||
return [ $value, $version, $curInfo['asOf'] ];
|
||
}
|
||
|
||
/**
|
||
* @param string $key
|
||
* @return bool Success
|
||
*/
|
||
private function claimStampedeLock( $key ) {
|
||
// Note that locking is not bypassed due to I/O errors; this avoids stampedes
|
||
return $this->cache->add( self::$MUTEX_KEY_PREFIX . $key, 1, self::$LOCK_TTL );
|
||
}
|
||
|
||
/**
|
||
* @param string $key
|
||
* @param bool $hasLock
|
||
*/
|
||
private function yieldStampedeLock( $key, $hasLock ) {
|
||
if ( $hasLock ) {
|
||
// The backend might be a mcrouter proxy set to broadcast DELETE to *all* the local
|
||
// datacenter cache servers via OperationSelectorRoute (for increased consistency).
|
||
// Since that would be excessive for these locks, use TOUCH to expire the key.
|
||
$this->cache->changeTTL( self::$MUTEX_KEY_PREFIX . $key, $this->getCurrentTime() - 60 );
|
||
}
|
||
}
|
||
|
||
/**
|
||
* @param float $age Age of volatile/interim key in seconds
|
||
* @return bool Whether the age of a volatile value is negligible
|
||
*/
|
||
private function isVolatileValueAgeNegligible( $age ) {
|
||
return ( $age < mt_rand( self::$RECENT_SET_LOW_MS, self::$RECENT_SET_HIGH_MS ) / 1e3 );
|
||
}
|
||
|
||
/**
|
||
* @param string $key
|
||
* @param string $kClass
|
||
* @param float $elapsed Seconds spent regenerating the value
|
||
* @param float $lockTSE
|
||
* @param bool $hasLock
|
||
* @return bool Whether it is OK to proceed with a key set operation
|
||
*/
|
||
private function checkAndSetCooloff( $key, $kClass, $elapsed, $lockTSE, $hasLock ) {
|
||
$this->stats->timing( "wanobjectcache.$kClass.regen_set_delay", 1e3 * $elapsed );
|
||
|
||
// If $lockTSE is set, the lock was bypassed because there was no stale/interim value,
|
||
// and $elapsed indicates that regeration is slow, then there is a risk of set()
|
||
// stampedes with large blobs. With a typical scale-out infrastructure, CPU and query
|
||
// load from $callback invocations is distributed among appservers and replica DBs,
|
||
// but cache operations for a given key route to a single cache server (e.g. striped
|
||
// consistent hashing).
|
||
if ( $lockTSE < 0 || $hasLock ) {
|
||
return true; // either not a priori hot or thread has the lock
|
||
} elseif ( $elapsed <= self::$SET_DELAY_HIGH_MS * 1e3 ) {
|
||
return true; // not enough time for threads to pile up
|
||
}
|
||
|
||
$this->cache->clearLastError();
|
||
if (
|
||
!$this->cache->add( self::$COOLOFF_KEY_PREFIX . $key, 1, self::$COOLOFF_TTL ) &&
|
||
// Don't treat failures due to I/O errors as the key being in cooloff
|
||
$this->cache->getLastError() === BagOStuff::ERR_NONE
|
||
) {
|
||
$this->stats->increment( "wanobjectcache.$kClass.cooloff_bounce" );
|
||
|
||
return false;
|
||
}
|
||
|
||
return true;
|
||
}
|
||
|
||
/**
|
||
* @param mixed $value
|
||
* @param float|null $curTTL
|
||
* @param array $curInfo
|
||
* @param callable|null $touchedCallback
|
||
* @return array (current time left or null, UNIX timestamp of last purge or null)
|
||
* @note Callable type hints are not used to avoid class-autoloading
|
||
*/
|
||
private function resolveCTL( $value, $curTTL, $curInfo, $touchedCallback ) {
|
||
if ( $touchedCallback === null || $value === false ) {
|
||
return [ $curTTL, max( $curInfo['tombAsOf'], $curInfo['lastCKPurge'] ) ];
|
||
}
|
||
|
||
$touched = $touchedCallback( $value );
|
||
if ( $touched !== null && $touched >= $curInfo['asOf'] ) {
|
||
$curTTL = min( $curTTL, self::$TINY_NEGATIVE, $curInfo['asOf'] - $touched );
|
||
}
|
||
|
||
return [ $curTTL, max( $curInfo['tombAsOf'], $curInfo['lastCKPurge'], $touched ) ];
|
||
}
|
||
|
||
/**
|
||
* @param mixed $value
|
||
* @param float|null $lastPurge
|
||
* @param callable|null $touchedCallback
|
||
* @return float|null UNIX timestamp of last purge or null
|
||
* @note Callable type hints are not used to avoid class-autoloading
|
||
*/
|
||
private function resolveTouched( $value, $lastPurge, $touchedCallback ) {
|
||
return ( $touchedCallback === null || $value === false )
|
||
? $lastPurge // nothing to derive the "touched timestamp" from
|
||
: max( $touchedCallback( $value ), $lastPurge );
|
||
}
|
||
|
||
/**
|
||
* @param string $key
|
||
* @param float $minAsOf Minimum acceptable "as of" timestamp
|
||
* @return array (cached value or false, cache key metadata map)
|
||
*/
|
||
private function getInterimValue( $key, $minAsOf ) {
|
||
$now = $this->getCurrentTime();
|
||
|
||
if ( $this->useInterimHoldOffCaching ) {
|
||
$wrapped = $this->cache->get( self::$INTERIM_KEY_PREFIX . $key );
|
||
|
||
list( $value, $keyInfo ) = $this->unwrap( $wrapped, $now );
|
||
if ( $this->isValid( $value, $keyInfo['asOf'], $minAsOf ) ) {
|
||
return [ $value, $keyInfo ];
|
||
}
|
||
}
|
||
|
||
return $this->unwrap( false, $now );
|
||
}
|
||
|
||
/**
|
||
* @param string $key
|
||
* @param mixed $value
|
||
* @param int $ttl
|
||
* @param int|null $version Value version number
|
||
* @param float $walltime How long it took to generate the value in seconds
|
||
*/
|
||
private function setInterimValue( $key, $value, $ttl, $version, $walltime ) {
|
||
$ttl = max( self::$INTERIM_KEY_TTL, (int)$ttl );
|
||
|
||
$wrapped = $this->wrap( $value, $ttl, $version, $this->getCurrentTime(), $walltime );
|
||
$this->cache->merge(
|
||
self::$INTERIM_KEY_PREFIX . $key,
|
||
function () use ( $wrapped ) {
|
||
return $wrapped;
|
||
},
|
||
$ttl,
|
||
1
|
||
);
|
||
}
|
||
|
||
/**
|
||
* @param mixed $busyValue
|
||
* @return mixed
|
||
*/
|
||
private function resolveBusyValue( $busyValue ) {
|
||
return ( $busyValue instanceof Closure ) ? $busyValue() : $busyValue;
|
||
}
|
||
|
||
/**
|
||
* Method to fetch multiple cache keys at once with regeneration
|
||
*
|
||
* This works the same as getWithSetCallback() except:
|
||
* - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys()
|
||
* - b) The $callback argument expects a callback taking the following arguments:
|
||
* - $id: ID of an entity to query
|
||
* - $oldValue : the prior cache value or false if none was present
|
||
* - &$ttl : a reference to the new value TTL in seconds
|
||
* - &$setOpts : a reference to options for set() which can be altered
|
||
* - $oldAsOf : generation UNIX timestamp of $oldValue or null if not present
|
||
* Aside from the additional $id argument, the other arguments function the same
|
||
* way they do in getWithSetCallback().
|
||
* - c) The return value is a map of (cache key => value) in the order of $keyedIds
|
||
*
|
||
* @see WANObjectCache::getWithSetCallback()
|
||
* @see WANObjectCache::getMultiWithUnionSetCallback()
|
||
*
|
||
* Example usage:
|
||
* @code
|
||
* $rows = $cache->getMultiWithSetCallback(
|
||
* // Map of cache keys to entity IDs
|
||
* $cache->makeMultiKeys(
|
||
* $this->fileVersionIds(),
|
||
* function ( $id ) use ( $cache ) {
|
||
* return $cache->makeKey( 'file-version', $id );
|
||
* }
|
||
* ),
|
||
* // Time-to-live (in seconds)
|
||
* $cache::TTL_DAY,
|
||
* // Function that derives the new key value
|
||
* function ( $id, $oldValue, &$ttl, array &$setOpts ) {
|
||
* $dbr = wfGetDB( DB_REPLICA );
|
||
* // Account for any snapshot/replica DB lag
|
||
* $setOpts += Database::getCacheSetOptions( $dbr );
|
||
*
|
||
* // Load the row for this file
|
||
* $queryInfo = File::getQueryInfo();
|
||
* $row = $dbr->selectRow(
|
||
* $queryInfo['tables'],
|
||
* $queryInfo['fields'],
|
||
* [ 'id' => $id ],
|
||
* __METHOD__,
|
||
* [],
|
||
* $queryInfo['joins']
|
||
* );
|
||
*
|
||
* return $row ? (array)$row : false;
|
||
* },
|
||
* [
|
||
* // Process cache for 30 seconds
|
||
* 'pcTTL' => 30,
|
||
* // Use a dedicated 500 item cache (initialized on-the-fly)
|
||
* 'pcGroup' => 'file-versions:500'
|
||
* ]
|
||
* );
|
||
* $files = array_map( [ __CLASS__, 'newFromRow' ], $rows );
|
||
* @endcode
|
||
*
|
||
* @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys()
|
||
* @param int $ttl Seconds to live for key updates
|
||
* @param callable $callback Callback the yields entity regeneration callbacks
|
||
* @param array $opts Options map
|
||
* @return mixed[] Map of (cache key => value) in the same order as $keyedIds
|
||
* @since 1.28
|
||
*/
|
||
final public function getMultiWithSetCallback(
|
||
ArrayIterator $keyedIds, $ttl, callable $callback, array $opts = []
|
||
) {
|
||
// Load required keys into process cache in one go
|
||
$this->warmupCache = $this->getRawKeysForWarmup(
|
||
$this->getNonProcessCachedMultiKeys( $keyedIds, $opts ),
|
||
$opts['checkKeys'] ?? []
|
||
);
|
||
$this->warmupKeyMisses = 0;
|
||
|
||
// Wrap $callback to match the getWithSetCallback() format while passing $id to $callback
|
||
$id = null; // current entity ID
|
||
$func = function ( $oldValue, &$ttl, &$setOpts, $oldAsOf ) use ( $callback, &$id ) {
|
||
return $callback( $id, $oldValue, $ttl, $setOpts, $oldAsOf );
|
||
};
|
||
|
||
$values = [];
|
||
foreach ( $keyedIds as $key => $id ) { // preserve order
|
||
$values[$key] = $this->getWithSetCallback( $key, $ttl, $func, $opts );
|
||
}
|
||
|
||
$this->warmupCache = [];
|
||
|
||
return $values;
|
||
}
|
||
|
||
/**
|
||
* Method to fetch/regenerate multiple cache keys at once
|
||
*
|
||
* This works the same as getWithSetCallback() except:
|
||
* - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys()
|
||
* - b) The $callback argument expects a callback returning a map of (ID => new value)
|
||
* for all entity IDs in $ids and it takes the following arguments:
|
||
* - $ids: a list of entity IDs that require cache regeneration
|
||
* - &$ttls: a reference to the (entity ID => new TTL) map
|
||
* - &$setOpts: a reference to options for set() which can be altered
|
||
* - c) The return value is a map of (cache key => value) in the order of $keyedIds
|
||
* - d) The "lockTSE" and "busyValue" options are ignored
|
||
*
|
||
* @see WANObjectCache::getWithSetCallback()
|
||
* @see WANObjectCache::getMultiWithSetCallback()
|
||
*
|
||
* @warning Usage of this method appears to have caused cache corruption, see T235188.
|
||
* This method should not be used until the root cause of T235188 has been resolved
|
||
* and I94c6f9ba7b9caeeb has been reverted.
|
||
*
|
||
* Example usage:
|
||
* @code
|
||
* $rows = $cache->getMultiWithUnionSetCallback(
|
||
* // Map of cache keys to entity IDs
|
||
* $cache->makeMultiKeys(
|
||
* $this->fileVersionIds(),
|
||
* function ( $id ) use ( $cache ) {
|
||
* return $cache->makeKey( 'file-version', $id );
|
||
* }
|
||
* ),
|
||
* // Time-to-live (in seconds)
|
||
* $cache::TTL_DAY,
|
||
* // Function that derives the new key value
|
||
* function ( array $ids, array &$ttls, array &$setOpts ) {
|
||
* $dbr = wfGetDB( DB_REPLICA );
|
||
* // Account for any snapshot/replica DB lag
|
||
* $setOpts += Database::getCacheSetOptions( $dbr );
|
||
*
|
||
* // Load the rows for these files
|
||
* $rows = [];
|
||
* $queryInfo = File::getQueryInfo();
|
||
* $res = $dbr->select(
|
||
* $queryInfo['tables'],
|
||
* $queryInfo['fields'],
|
||
* [ 'id' => $ids ],
|
||
* __METHOD__,
|
||
* [],
|
||
* $queryInfo['joins']
|
||
* );
|
||
* foreach ( $res as $row ) {
|
||
* $rows[$row->id] = $row;
|
||
* $mtime = wfTimestamp( TS_UNIX, $row->timestamp );
|
||
* $ttls[$row->id] = $this->adaptiveTTL( $mtime, $ttls[$row->id] );
|
||
* }
|
||
*
|
||
* return $rows;
|
||
* },
|
||
* ]
|
||
* );
|
||
* $files = array_map( [ __CLASS__, 'newFromRow' ], $rows );
|
||
* @endcode
|
||
*
|
||
* @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys()
|
||
* @param int $ttl Seconds to live for key updates
|
||
* @param callable $callback Callback the yields entity regeneration callbacks
|
||
* @param array $opts Options map
|
||
* @return mixed[] Map of (cache key => value) in the same order as $keyedIds
|
||
* @since 1.30
|
||
*/
|
||
final public function getMultiWithUnionSetCallback(
|
||
ArrayIterator $keyedIds, $ttl, callable $callback, array $opts = []
|
||
) {
|
||
$checkKeys = $opts['checkKeys'] ?? [];
|
||
unset( $opts['lockTSE'] ); // incompatible
|
||
unset( $opts['busyValue'] ); // incompatible
|
||
|
||
// Load required keys into process cache in one go
|
||
$keysByIdGet = $this->getNonProcessCachedMultiKeys( $keyedIds, $opts );
|
||
$this->warmupCache = $this->getRawKeysForWarmup( $keysByIdGet, $checkKeys );
|
||
$this->warmupKeyMisses = 0;
|
||
|
||
// IDs of entities known to be in need of regeneration
|
||
$idsRegen = [];
|
||
|
||
// Find out which keys are missing/deleted/stale
|
||
$curTTLs = [];
|
||
$asOfs = [];
|
||
$curByKey = $this->getMulti( $keysByIdGet, $curTTLs, $checkKeys, $asOfs );
|
||
foreach ( $keysByIdGet as $id => $key ) {
|
||
if ( !array_key_exists( $key, $curByKey ) || $curTTLs[$key] < 0 ) {
|
||
$idsRegen[] = $id;
|
||
}
|
||
}
|
||
|
||
// Run the callback to populate the regeneration value map for all required IDs
|
||
$newSetOpts = [];
|
||
$newTTLsById = array_fill_keys( $idsRegen, $ttl );
|
||
$newValsById = $idsRegen ? $callback( $idsRegen, $newTTLsById, $newSetOpts ) : [];
|
||
|
||
// Wrap $callback to match the getWithSetCallback() format while passing $id to $callback
|
||
$id = null; // current entity ID
|
||
$func = function ( $oldValue, &$ttl, &$setOpts, $oldAsOf )
|
||
use ( $callback, &$id, $newValsById, $newTTLsById, $newSetOpts )
|
||
{
|
||
if ( array_key_exists( $id, $newValsById ) ) {
|
||
// Value was already regerated as expected, so use the value in $newValsById
|
||
$newValue = $newValsById[$id];
|
||
$ttl = $newTTLsById[$id];
|
||
$setOpts = $newSetOpts;
|
||
} else {
|
||
// Pre-emptive/popularity refresh and version mismatch cases are not detected
|
||
// above and thus $newValsById has no entry. Run $callback on this single entity.
|
||
$ttls = [ $id => $ttl ];
|
||
$newValue = $callback( [ $id ], $ttls, $setOpts )[$id];
|
||
$ttl = $ttls[$id];
|
||
}
|
||
|
||
return $newValue;
|
||
};
|
||
|
||
// Run the cache-aside logic using warmupCache instead of persistent cache queries
|
||
$values = [];
|
||
foreach ( $keyedIds as $key => $id ) { // preserve order
|
||
$values[$key] = $this->getWithSetCallback( $key, $ttl, $func, $opts );
|
||
}
|
||
|
||
$this->warmupCache = [];
|
||
|
||
return $values;
|
||
}
|
||
|
||
/**
|
||
* Set a key to soon expire in the local cluster if it pre-dates $purgeTimestamp
|
||
*
|
||
* This sets stale keys' time-to-live at HOLDOFF_TTL seconds, which both avoids
|
||
* broadcasting in mcrouter setups and also avoids races with new tombstones.
|
||
*
|
||
* @param string $key Cache key
|
||
* @param int $purgeTimestamp UNIX timestamp of purge
|
||
* @param bool &$isStale Whether the key is stale
|
||
* @return bool Success
|
||
* @since 1.28
|
||
*/
|
||
final public function reap( $key, $purgeTimestamp, &$isStale = false ) {
|
||
$minAsOf = $purgeTimestamp + self::HOLDOFF_TTL;
|
||
$wrapped = $this->cache->get( self::$VALUE_KEY_PREFIX . $key );
|
||
if ( is_array( $wrapped ) && $wrapped[self::$FLD_TIME] < $minAsOf ) {
|
||
$isStale = true;
|
||
$this->logger->warning( "Reaping stale value key '$key'." );
|
||
$ttlReap = self::HOLDOFF_TTL; // avoids races with tombstone creation
|
||
$ok = $this->cache->changeTTL( self::$VALUE_KEY_PREFIX . $key, $ttlReap );
|
||
if ( !$ok ) {
|
||
$this->logger->error( "Could not complete reap of key '$key'." );
|
||
}
|
||
|
||
return $ok;
|
||
}
|
||
|
||
$isStale = false;
|
||
|
||
return true;
|
||
}
|
||
|
||
/**
|
||
* Set a "check" key to soon expire in the local cluster if it pre-dates $purgeTimestamp
|
||
*
|
||
* @param string $key Cache key
|
||
* @param int $purgeTimestamp UNIX timestamp of purge
|
||
* @param bool &$isStale Whether the key is stale
|
||
* @return bool Success
|
||
* @since 1.28
|
||
*/
|
||
final public function reapCheckKey( $key, $purgeTimestamp, &$isStale = false ) {
|
||
$purge = $this->parsePurgeValue( $this->cache->get( self::$TIME_KEY_PREFIX . $key ) );
|
||
if ( $purge && $purge[self::$PURGE_TIME] < $purgeTimestamp ) {
|
||
$isStale = true;
|
||
$this->logger->warning( "Reaping stale check key '$key'." );
|
||
$ok = $this->cache->changeTTL( self::$TIME_KEY_PREFIX . $key, self::TTL_SECOND );
|
||
if ( !$ok ) {
|
||
$this->logger->error( "Could not complete reap of check key '$key'." );
|
||
}
|
||
|
||
return $ok;
|
||
}
|
||
|
||
$isStale = false;
|
||
|
||
return false;
|
||
}
|
||
|
||
/**
|
||
* @see BagOStuff::makeKey()
|
||
* @param string $class Key class
|
||
* @param string ...$components Key components (starting with a key collection name)
|
||
* @return string Colon-delimited list of $keyspace followed by escaped components
|
||
* @since 1.27
|
||
*/
|
||
public function makeKey( $class, ...$components ) {
|
||
return $this->cache->makeKey( ...func_get_args() );
|
||
}
|
||
|
||
/**
|
||
* @see BagOStuff::makeGlobalKey()
|
||
* @param string $class Key class
|
||
* @param string ...$components Key components (starting with a key collection name)
|
||
* @return string Colon-delimited list of $keyspace followed by escaped components
|
||
* @since 1.27
|
||
*/
|
||
public function makeGlobalKey( $class, ...$components ) {
|
||
return $this->cache->makeGlobalKey( ...func_get_args() );
|
||
}
|
||
|
||
/**
|
||
* Hash a possibly long string into a suitable component for makeKey()/makeGlobalKey()
|
||
*
|
||
* @param string $component A raw component used in building a cache key
|
||
* @return string 64 character HMAC using a stable secret for public collision resistance
|
||
* @since 1.34
|
||
*/
|
||
public function hash256( $component ) {
|
||
return hash_hmac( 'sha256', $component, $this->secret );
|
||
}
|
||
|
||
/**
|
||
* Get an iterator of (cache key => entity ID) for a list of entity IDs
|
||
*
|
||
* The callback takes an ID string and returns a key via makeKey()/makeGlobalKey().
|
||
* There should be no network nor filesystem I/O used in the callback. The entity
|
||
* ID/key mapping must be 1:1 or an exception will be thrown. If hashing is needed,
|
||
* then use the hash256() method.
|
||
*
|
||
* Example usage for the default keyspace:
|
||
* @code
|
||
* $keyedIds = $cache->makeMultiKeys(
|
||
* $modules,
|
||
* function ( $module ) use ( $cache ) {
|
||
* return $cache->makeKey( 'module-info', $module );
|
||
* }
|
||
* );
|
||
* @endcode
|
||
*
|
||
* Example usage for mixed default and global keyspace:
|
||
* @code
|
||
* $keyedIds = $cache->makeMultiKeys(
|
||
* $filters,
|
||
* function ( $filter ) use ( $cache ) {
|
||
* return ( strpos( $filter, 'central:' ) === 0 )
|
||
* ? $cache->makeGlobalKey( 'regex-filter', $filter )
|
||
* : $cache->makeKey( 'regex-filter', $filter )
|
||
* }
|
||
* );
|
||
* @endcode
|
||
*
|
||
* Example usage with hashing:
|
||
* @code
|
||
* $keyedIds = $cache->makeMultiKeys(
|
||
* $urls,
|
||
* function ( $url ) use ( $cache ) {
|
||
* return $cache->makeKey( 'url-info', $cache->hash256( $url ) );
|
||
* }
|
||
* );
|
||
* @endcode
|
||
*
|
||
* @see WANObjectCache::makeKey()
|
||
* @see WANObjectCache::makeGlobalKey()
|
||
* @see WANObjectCache::hash256()
|
||
*
|
||
* @param string[]|int[] $ids List of entity IDs
|
||
* @param callable $keyCallback Function returning makeKey()/makeGlobalKey() on the input ID
|
||
* @return ArrayIterator Iterator of (cache key => ID); order of $ids is preserved
|
||
* @throws UnexpectedValueException
|
||
* @since 1.28
|
||
*/
|
||
final public function makeMultiKeys( array $ids, $keyCallback ) {
|
||
$idByKey = [];
|
||
foreach ( $ids as $id ) {
|
||
// Discourage triggering of automatic makeKey() hashing in some backends
|
||
if ( strlen( $id ) > 64 ) {
|
||
$this->logger->warning( __METHOD__ . ": long ID '$id'; use hash256()" );
|
||
}
|
||
$key = $keyCallback( $id, $this );
|
||
// Edge case: ignore key collisions due to duplicate $ids like "42" and 42
|
||
if ( !isset( $idByKey[$key] ) ) {
|
||
$idByKey[$key] = $id;
|
||
} elseif ( (string)$id !== (string)$idByKey[$key] ) {
|
||
throw new UnexpectedValueException(
|
||
"Cache key collision; IDs ('$id','{$idByKey[$key]}') map to '$key'"
|
||
);
|
||
}
|
||
}
|
||
|
||
return new ArrayIterator( $idByKey );
|
||
}
|
||
|
||
/**
|
||
* Get an (ID => value) map from (i) a non-unique list of entity IDs, and (ii) the list
|
||
* of corresponding entity values by first appearance of each ID in the entity ID list
|
||
*
|
||
* For use with getMultiWithSetCallback() and getMultiWithUnionSetCallback().
|
||
*
|
||
* *Only* use this method if the entity ID/key mapping is trivially 1:1 without exception.
|
||
* Key generation method must utitilize the *full* entity ID in the key (not a hash of it).
|
||
*
|
||
* Example usage:
|
||
* @code
|
||
* $poems = $cache->getMultiWithSetCallback(
|
||
* $cache->makeMultiKeys(
|
||
* $uuids,
|
||
* function ( $uuid ) use ( $cache ) {
|
||
* return $cache->makeKey( 'poem', $uuid );
|
||
* }
|
||
* ),
|
||
* $cache::TTL_DAY,
|
||
* function ( $uuid ) use ( $url ) {
|
||
* return $this->http->run( [ 'method' => 'GET', 'url' => "$url/$uuid" ] );
|
||
* }
|
||
* );
|
||
* $poemsByUUID = $cache->multiRemap( $uuids, $poems );
|
||
* @endcode
|
||
*
|
||
* @see WANObjectCache::makeMultiKeys()
|
||
* @see WANObjectCache::getMultiWithSetCallback()
|
||
* @see WANObjectCache::getMultiWithUnionSetCallback()
|
||
*
|
||
* @param string[]|int[] $ids Entity ID list makeMultiKeys()
|
||
* @param mixed[] $res Result of getMultiWithSetCallback()/getMultiWithUnionSetCallback()
|
||
* @return mixed[] Map of (ID => value); order of $ids is preserved
|
||
* @since 1.34
|
||
*/
|
||
final public function multiRemap( array $ids, array $res ) {
|
||
if ( count( $ids ) !== count( $res ) ) {
|
||
// If makeMultiKeys() is called on a list of non-unique IDs, then the resulting
|
||
// ArrayIterator will have less entries due to "first appearance" de-duplication
|
||
$ids = array_keys( array_flip( $ids ) );
|
||
if ( count( $ids ) !== count( $res ) ) {
|
||
throw new UnexpectedValueException( "Multi-key result does not match ID list" );
|
||
}
|
||
}
|
||
|
||
return array_combine( $ids, $res );
|
||
}
|
||
|
||
/**
|
||
* Get the "last error" registered; clearLastError() should be called manually
|
||
* @return int ERR_* class constant for the "last error" registry
|
||
*/
|
||
final public function getLastError() {
|
||
$code = $this->cache->getLastError();
|
||
switch ( $code ) {
|
||
case BagOStuff::ERR_NONE:
|
||
return self::ERR_NONE;
|
||
case BagOStuff::ERR_NO_RESPONSE:
|
||
return self::ERR_NO_RESPONSE;
|
||
case BagOStuff::ERR_UNREACHABLE:
|
||
return self::ERR_UNREACHABLE;
|
||
default:
|
||
return self::ERR_UNEXPECTED;
|
||
}
|
||
}
|
||
|
||
/**
|
||
* Clear the "last error" registry
|
||
*/
|
||
final public function clearLastError() {
|
||
$this->cache->clearLastError();
|
||
}
|
||
|
||
/**
|
||
* Clear the in-process caches; useful for testing
|
||
*
|
||
* @since 1.27
|
||
*/
|
||
public function clearProcessCache() {
|
||
$this->processCaches = [];
|
||
}
|
||
|
||
/**
|
||
* Enable or disable the use of brief caching for tombstoned keys
|
||
*
|
||
* When a key is purged via delete(), there normally is a period where caching
|
||
* is hold-off limited to an extremely short time. This method will disable that
|
||
* caching, forcing the callback to run for any of:
|
||
* - WANObjectCache::getWithSetCallback()
|
||
* - WANObjectCache::getMultiWithSetCallback()
|
||
* - WANObjectCache::getMultiWithUnionSetCallback()
|
||
*
|
||
* This is useful when both:
|
||
* - a) the database used by the callback is known to be up-to-date enough
|
||
* for some particular purpose (e.g. replica DB has applied transaction X)
|
||
* - b) the caller needs to exploit that fact, and therefore needs to avoid the
|
||
* use of inherently volatile and possibly stale interim keys
|
||
*
|
||
* @see WANObjectCache::delete()
|
||
* @param bool $enabled Whether to enable interim caching
|
||
* @since 1.31
|
||
*/
|
||
final public function useInterimHoldOffCaching( $enabled ) {
|
||
$this->useInterimHoldOffCaching = $enabled;
|
||
}
|
||
|
||
/**
|
||
* @param int $flag ATTR_* class constant
|
||
* @return int QOS_* class constant
|
||
* @since 1.28
|
||
*/
|
||
public function getQoS( $flag ) {
|
||
return $this->cache->getQoS( $flag );
|
||
}
|
||
|
||
/**
|
||
* Get a TTL that is higher for objects that have not changed recently
|
||
*
|
||
* This is useful for keys that get explicit purges and DB or purge relay
|
||
* lag is a potential concern (especially how it interacts with CDN cache)
|
||
*
|
||
* Example usage:
|
||
* @code
|
||
* // Last-modified time of page
|
||
* $mtime = wfTimestamp( TS_UNIX, $page->getTimestamp() );
|
||
* // Get adjusted TTL. If $mtime is 3600 seconds ago and $minTTL/$factor left at
|
||
* // defaults, then $ttl is 3600 * .2 = 720. If $minTTL was greater than 720, then
|
||
* // $ttl would be $minTTL. If $maxTTL was smaller than 720, $ttl would be $maxTTL.
|
||
* $ttl = $cache->adaptiveTTL( $mtime, $cache::TTL_DAY );
|
||
* @endcode
|
||
*
|
||
* Another use case is when there are no applicable "last modified" fields in the DB,
|
||
* and there are too many dependencies for explicit purges to be viable, and the rate of
|
||
* change to relevant content is unstable, and it is highly valued to have the cached value
|
||
* be as up-to-date as possible.
|
||
*
|
||
* Example usage:
|
||
* @code
|
||
* $query = "<some complex query>";
|
||
* $idListFromComplexQuery = $cache->getWithSetCallback(
|
||
* $cache->makeKey( 'complex-graph-query', $hashOfQuery ),
|
||
* GraphQueryClass::STARTING_TTL,
|
||
* function ( $oldValue, &$ttl, array &$setOpts, $oldAsOf ) use ( $query, $cache ) {
|
||
* $gdb = $this->getReplicaGraphDbConnection();
|
||
* // Account for any snapshot/replica DB lag
|
||
* $setOpts += GraphDatabase::getCacheSetOptions( $gdb );
|
||
*
|
||
* $newList = iterator_to_array( $gdb->query( $query ) );
|
||
* sort( $newList, SORT_NUMERIC ); // normalize
|
||
*
|
||
* $minTTL = GraphQueryClass::MIN_TTL;
|
||
* $maxTTL = GraphQueryClass::MAX_TTL;
|
||
* if ( $oldValue !== false ) {
|
||
* // Note that $oldAsOf is the last time this callback ran
|
||
* $ttl = ( $newList === $oldValue )
|
||
* // No change: cache for 150% of the age of $oldValue
|
||
* ? $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, 1.5 )
|
||
* // Changed: cache for 50% of the age of $oldValue
|
||
* : $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, .5 );
|
||
* }
|
||
*
|
||
* return $newList;
|
||
* },
|
||
* [
|
||
* // Keep stale values around for doing comparisons for TTL calculations.
|
||
* // High values improve long-tail keys hit-rates, though might waste space.
|
||
* 'staleTTL' => GraphQueryClass::GRACE_TTL
|
||
* ]
|
||
* );
|
||
* @endcode
|
||
*
|
||
* @param int|float $mtime UNIX timestamp
|
||
* @param int $maxTTL Maximum TTL (seconds)
|
||
* @param int $minTTL Minimum TTL (seconds); Default: 30
|
||
* @param float $factor Value in the range (0,1); Default: .2
|
||
* @return int Adaptive TTL
|
||
* @since 1.28
|
||
*/
|
||
public function adaptiveTTL( $mtime, $maxTTL, $minTTL = 30, $factor = 0.2 ) {
|
||
if ( is_float( $mtime ) || ctype_digit( $mtime ) ) {
|
||
$mtime = (int)$mtime; // handle fractional seconds and string integers
|
||
}
|
||
|
||
if ( !is_int( $mtime ) || $mtime <= 0 ) {
|
||
return $minTTL; // no last-modified time provided
|
||
}
|
||
|
||
$age = $this->getCurrentTime() - $mtime;
|
||
|
||
return (int)min( $maxTTL, max( $minTTL, $factor * $age ) );
|
||
}
|
||
|
||
/**
|
||
* @return int Number of warmup key cache misses last round
|
||
* @since 1.30
|
||
*/
|
||
final public function getWarmupKeyMisses() {
|
||
return $this->warmupKeyMisses;
|
||
}
|
||
|
||
/**
|
||
* Do the actual async bus purge of a key
|
||
*
|
||
* This must set the key to "PURGED:<UNIX timestamp>:<holdoff>"
|
||
*
|
||
* @param string $key Cache key
|
||
* @param int $ttl Seconds to keep the tombstone around
|
||
* @param int $holdoff HOLDOFF_* constant controlling how long to ignore sets for this key
|
||
* @return bool Success
|
||
*/
|
||
protected function relayPurge( $key, $ttl, $holdoff ) {
|
||
if ( $this->mcrouterAware ) {
|
||
// See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup
|
||
// Wildcards select all matching routes, e.g. the WAN cluster on all DCs
|
||
$ok = $this->cache->set(
|
||
"/*/{$this->cluster}/{$key}",
|
||
$this->makePurgeValue( $this->getCurrentTime(), $holdoff ),
|
||
$ttl
|
||
);
|
||
} else {
|
||
// Some other proxy handles broadcasting or there is only one datacenter
|
||
$ok = $this->cache->set(
|
||
$key,
|
||
$this->makePurgeValue( $this->getCurrentTime(), $holdoff ),
|
||
$ttl
|
||
);
|
||
}
|
||
|
||
return $ok;
|
||
}
|
||
|
||
/**
|
||
* Do the actual async bus delete of a key
|
||
*
|
||
* @param string $key Cache key
|
||
* @return bool Success
|
||
*/
|
||
protected function relayDelete( $key ) {
|
||
if ( $this->mcrouterAware ) {
|
||
// See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup
|
||
// Wildcards select all matching routes, e.g. the WAN cluster on all DCs
|
||
$ok = $this->cache->delete( "/*/{$this->cluster}/{$key}" );
|
||
} else {
|
||
// Some other proxy handles broadcasting or there is only one datacenter
|
||
$ok = $this->cache->delete( $key );
|
||
}
|
||
|
||
return $ok;
|
||
}
|
||
|
||
/**
|
||
* @param string $key
|
||
* @param int $ttl Seconds to live
|
||
* @param callable $callback
|
||
* @param array $opts
|
||
* @return bool Success
|
||
* @note Callable type hints are not used to avoid class-autoloading
|
||
*/
|
||
private function scheduleAsyncRefresh( $key, $ttl, $callback, $opts ) {
|
||
if ( !$this->asyncHandler ) {
|
||
return false;
|
||
}
|
||
// Update the cache value later, such during post-send of an HTTP request
|
||
$func = $this->asyncHandler;
|
||
$func( function () use ( $key, $ttl, $callback, $opts ) {
|
||
$opts['minAsOf'] = INF; // force a refresh
|
||
$this->fetchOrRegenerate( $key, $ttl, $callback, $opts );
|
||
} );
|
||
|
||
return true;
|
||
}
|
||
|
||
/**
|
||
* Check if a key is fresh or in the grace window and thus due for randomized reuse
|
||
*
|
||
* If $curTTL > 0 (e.g. not expired) this returns true. Otherwise, the chance of returning
|
||
* true decrease steadily from 100% to 0% as the |$curTTL| moves from 0 to $graceTTL seconds.
|
||
* This handles widely varying levels of cache access traffic.
|
||
*
|
||
* If $curTTL <= -$graceTTL (e.g. already expired), then this returns false.
|
||
*
|
||
* @param float $curTTL Approximate TTL left on the key if present
|
||
* @param int $graceTTL Consider using stale values if $curTTL is greater than this
|
||
* @return bool
|
||
*/
|
||
private function isAliveOrInGracePeriod( $curTTL, $graceTTL ) {
|
||
if ( $curTTL > 0 ) {
|
||
return true;
|
||
} elseif ( $graceTTL <= 0 ) {
|
||
return false;
|
||
}
|
||
|
||
$ageStale = abs( $curTTL ); // seconds of staleness
|
||
$curGTTL = ( $graceTTL - $ageStale ); // current grace-time-to-live
|
||
if ( $curGTTL <= 0 ) {
|
||
return false; // already out of grace period
|
||
}
|
||
|
||
// Chance of using a stale value is the complement of the chance of refreshing it
|
||
return !$this->worthRefreshExpiring( $curGTTL, $graceTTL );
|
||
}
|
||
|
||
/**
|
||
* Check if a key is nearing expiration and thus due for randomized regeneration
|
||
*
|
||
* This returns false if $curTTL >= $lowTTL. Otherwise, the chance of returning true
|
||
* increases steadily from 0% to 100% as the $curTTL moves from $lowTTL to 0 seconds.
|
||
* This handles widely varying levels of cache access traffic.
|
||
*
|
||
* If $curTTL <= 0 (e.g. already expired), then this returns false.
|
||
*
|
||
* @param float $curTTL Approximate TTL left on the key if present
|
||
* @param float $lowTTL Consider a refresh when $curTTL is less than this
|
||
* @return bool
|
||
*/
|
||
protected function worthRefreshExpiring( $curTTL, $lowTTL ) {
|
||
if ( $lowTTL <= 0 ) {
|
||
return false;
|
||
} elseif ( $curTTL >= $lowTTL ) {
|
||
return false;
|
||
} elseif ( $curTTL <= 0 ) {
|
||
return false;
|
||
}
|
||
|
||
$chance = ( 1 - $curTTL / $lowTTL );
|
||
|
||
// @phan-suppress-next-line PhanTypeMismatchArgumentInternal
|
||
return mt_rand( 1, 1e9 ) <= 1e9 * $chance;
|
||
}
|
||
|
||
/**
|
||
* Check if a key is due for randomized regeneration due to its popularity
|
||
*
|
||
* This is used so that popular keys can preemptively refresh themselves for higher
|
||
* consistency (especially in the case of purge loss/delay). Unpopular keys can remain
|
||
* in cache with their high nominal TTL. This means popular keys keep good consistency,
|
||
* whether the data changes frequently or not, and long-tail keys get to stay in cache
|
||
* and get hits too. Similar to worthRefreshExpiring(), randomization is used.
|
||
*
|
||
* @param float $asOf UNIX timestamp of the value
|
||
* @param int $ageNew Age of key when this might recommend refreshing (seconds)
|
||
* @param int $timeTillRefresh Age of key when it should be refreshed if popular (seconds)
|
||
* @param float $now The current UNIX timestamp
|
||
* @return bool
|
||
*/
|
||
protected function worthRefreshPopular( $asOf, $ageNew, $timeTillRefresh, $now ) {
|
||
if ( $ageNew < 0 || $timeTillRefresh <= 0 ) {
|
||
return false;
|
||
}
|
||
|
||
$age = $now - $asOf;
|
||
$timeOld = $age - $ageNew;
|
||
if ( $timeOld <= 0 ) {
|
||
return false;
|
||
}
|
||
|
||
$popularHitsPerSec = 1;
|
||
// Lifecycle is: new, ramp-up refresh chance, full refresh chance.
|
||
// Note that the "expected # of refreshes" for the ramp-up time range is half
|
||
// of what it would be if P(refresh) was at its full value during that time range.
|
||
$refreshWindowSec = max( $timeTillRefresh - $ageNew - self::$RAMPUP_TTL / 2, 1 );
|
||
// P(refresh) * (# hits in $refreshWindowSec) = (expected # of refreshes)
|
||
// P(refresh) * ($refreshWindowSec * $popularHitsPerSec) = 1 (by definition)
|
||
// P(refresh) = 1/($refreshWindowSec * $popularHitsPerSec)
|
||
$chance = 1 / ( $popularHitsPerSec * $refreshWindowSec );
|
||
|
||
// Ramp up $chance from 0 to its nominal value over RAMPUP_TTL seconds to avoid stampedes
|
||
$chance *= ( $timeOld <= self::$RAMPUP_TTL ) ? $timeOld / self::$RAMPUP_TTL : 1;
|
||
|
||
// @phan-suppress-next-line PhanTypeMismatchArgumentInternal
|
||
return mt_rand( 1, 1e9 ) <= 1e9 * $chance;
|
||
}
|
||
|
||
/**
|
||
* Check if $value is not false, versioned (if needed), and not older than $minTime (if set)
|
||
*
|
||
* @param array|bool $value
|
||
* @param float $asOf The time $value was generated
|
||
* @param float $minAsOf Minimum acceptable "as of" timestamp
|
||
* @param float|null $purgeTime The last time the value was invalidated
|
||
* @return bool
|
||
*/
|
||
protected function isValid( $value, $asOf, $minAsOf, $purgeTime = null ) {
|
||
// Avoid reading any key not generated after the latest delete() or touch
|
||
$safeMinAsOf = max( $minAsOf, $purgeTime + self::$TINY_POSTIVE );
|
||
|
||
if ( $value === false ) {
|
||
return false;
|
||
} elseif ( $safeMinAsOf > 0 && $asOf < $minAsOf ) {
|
||
return false;
|
||
}
|
||
|
||
return true;
|
||
}
|
||
|
||
/**
|
||
* @param mixed $value
|
||
* @param int $ttl Seconds to live or zero for "indefinite"
|
||
* @param int|null $version Value version number or null if not versioned
|
||
* @param float $now Unix Current timestamp just before calling set()
|
||
* @param float $walltime How long it took to generate the value in seconds
|
||
* @return array
|
||
*/
|
||
private function wrap( $value, $ttl, $version, $now, $walltime ) {
|
||
// Returns keys in ascending integer order for PHP7 array packing:
|
||
// https://nikic.github.io/2014/12/22/PHPs-new-hashtable-implementation.html
|
||
$wrapped = [
|
||
self::$FLD_FORMAT_VERSION => self::$VERSION,
|
||
self::$FLD_VALUE => $value,
|
||
self::$FLD_TTL => $ttl,
|
||
self::$FLD_TIME => $now
|
||
];
|
||
if ( $version !== null ) {
|
||
$wrapped[self::$FLD_VALUE_VERSION] = $version;
|
||
}
|
||
if ( $walltime >= self::$GENERATION_SLOW_SEC ) {
|
||
$wrapped[self::$FLD_GENERATION_TIME] = $walltime;
|
||
}
|
||
|
||
return $wrapped;
|
||
}
|
||
|
||
/**
|
||
* @param array|string|bool $wrapped The entry at a cache key
|
||
* @param float $now Unix Current timestamp (preferrably pre-query)
|
||
* @return array (value or false if absent/tombstoned/malformed, value metadata map).
|
||
* The cache key metadata includes the following metadata:
|
||
* - asOf: UNIX timestamp of the value or null if there is no value
|
||
* - curTTL: remaining time-to-live (negative if tombstoned) or null if there is no value
|
||
* - version: value version number or null if the if there is no value
|
||
* - tombAsOf: UNIX timestamp of the tombstone or null if there is no tombstone
|
||
* @phan-return array{0:mixed,1:array{asOf:?mixed,curTTL:?int|float,version:?mixed,tombAsOf:?mixed}}
|
||
*/
|
||
private function unwrap( $wrapped, $now ) {
|
||
$value = false;
|
||
$info = [ 'asOf' => null, 'curTTL' => null, 'version' => null, 'tombAsOf' => null ];
|
||
|
||
if ( is_array( $wrapped ) ) {
|
||
// Entry expected to be a cached value; validate it
|
||
if (
|
||
( $wrapped[self::$FLD_FORMAT_VERSION] ?? null ) === self::$VERSION &&
|
||
$wrapped[self::$FLD_TIME] >= $this->epoch
|
||
) {
|
||
if ( $wrapped[self::$FLD_TTL] > 0 ) {
|
||
// Get the approximate time left on the key
|
||
$age = $now - $wrapped[self::$FLD_TIME];
|
||
$curTTL = max( $wrapped[self::$FLD_TTL] - $age, 0.0 );
|
||
} else {
|
||
// Key had no TTL, so the time left is unbounded
|
||
$curTTL = INF;
|
||
}
|
||
$value = $wrapped[self::$FLD_VALUE];
|
||
$info['version'] = $wrapped[self::$FLD_VALUE_VERSION] ?? null;
|
||
$info['asOf'] = $wrapped[self::$FLD_TIME];
|
||
$info['curTTL'] = $curTTL;
|
||
}
|
||
} else {
|
||
// Entry expected to be a tombstone; parse it
|
||
$purge = $this->parsePurgeValue( $wrapped );
|
||
if ( $purge !== false ) {
|
||
// Tombstoned keys should always have a negative current $ttl
|
||
$info['curTTL'] = min( $purge[self::$PURGE_TIME] - $now, self::$TINY_NEGATIVE );
|
||
$info['tombAsOf'] = $purge[self::$PURGE_TIME];
|
||
}
|
||
}
|
||
|
||
return [ $value, $info ];
|
||
}
|
||
|
||
/**
|
||
* @param string[] $keys
|
||
* @param string $prefix
|
||
* @return string[] Prefix keys; the order of $keys is preserved
|
||
*/
|
||
protected static function prefixCacheKeys( array $keys, $prefix ) {
|
||
$res = [];
|
||
foreach ( $keys as $key ) {
|
||
$res[] = $prefix . $key;
|
||
}
|
||
|
||
return $res;
|
||
}
|
||
|
||
/**
|
||
* @param string $key String of the format <scope>:<class>[:<class or variable>]...
|
||
* @return string A collection name to describe this class of key
|
||
*/
|
||
private function determineKeyClassForStats( $key ) {
|
||
$parts = explode( ':', $key, 3 );
|
||
// Sanity fallback in case the key was not made by makeKey.
|
||
// Replace dots because they are special in StatsD (T232907)
|
||
return strtr( $parts[1] ?? $parts[0], '.', '_' );
|
||
}
|
||
|
||
/**
|
||
* @param string|array|bool $value Possible string of the form "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
|
||
*/
|
||
private function parsePurgeValue( $value ) {
|
||
if ( !is_string( $value ) ) {
|
||
return false;
|
||
}
|
||
|
||
$segments = explode( ':', $value, 3 );
|
||
if (
|
||
!isset( $segments[0] ) ||
|
||
!isset( $segments[1] ) ||
|
||
"{$segments[0]}:" !== self::$PURGE_VAL_PREFIX
|
||
) {
|
||
return false;
|
||
}
|
||
|
||
if ( !isset( $segments[2] ) ) {
|
||
// Back-compat with old purge values without holdoff
|
||
$segments[2] = self::HOLDOFF_TTL;
|
||
}
|
||
|
||
if ( $segments[1] < $this->epoch ) {
|
||
// Values this old are ignored
|
||
return false;
|
||
}
|
||
|
||
return [
|
||
self::$PURGE_TIME => (float)$segments[1],
|
||
self::$PURGE_HOLDOFF => (int)$segments[2],
|
||
];
|
||
}
|
||
|
||
/**
|
||
* @param float $timestamp
|
||
* @param int $holdoff In seconds
|
||
* @return string Wrapped purge value
|
||
*/
|
||
private function makePurgeValue( $timestamp, $holdoff ) {
|
||
return self::$PURGE_VAL_PREFIX . (float)$timestamp . ':' . (int)$holdoff;
|
||
}
|
||
|
||
/**
|
||
* @param string $group
|
||
* @return MapCacheLRU
|
||
*/
|
||
private function getProcessCache( $group ) {
|
||
if ( !isset( $this->processCaches[$group] ) ) {
|
||
list( , $size ) = explode( ':', $group );
|
||
$this->processCaches[$group] = new MapCacheLRU( (int)$size );
|
||
if ( $this->wallClockOverride !== null ) {
|
||
$this->processCaches[$group]->setMockTime( $this->wallClockOverride );
|
||
}
|
||
}
|
||
|
||
return $this->processCaches[$group];
|
||
}
|
||
|
||
/**
|
||
* @param string $key
|
||
* @param int $version
|
||
* @return string
|
||
*/
|
||
private function getProcessCacheKey( $key, $version ) {
|
||
return $key . ' ' . (int)$version;
|
||
}
|
||
|
||
/**
|
||
* @param ArrayIterator $keys
|
||
* @param array $opts
|
||
* @return string[] Map of (ID => cache key)
|
||
*/
|
||
private function getNonProcessCachedMultiKeys( ArrayIterator $keys, array $opts ) {
|
||
$pcTTL = $opts['pcTTL'] ?? self::TTL_UNCACHEABLE;
|
||
|
||
$keysMissing = [];
|
||
if ( $pcTTL > 0 && $this->callbackDepth == 0 ) {
|
||
$version = $opts['version'] ?? null;
|
||
$pCache = $this->getProcessCache( $opts['pcGroup'] ?? self::PC_PRIMARY );
|
||
foreach ( $keys as $key => $id ) {
|
||
if ( !$pCache->has( $this->getProcessCacheKey( $key, $version ), $pcTTL ) ) {
|
||
$keysMissing[$id] = $key;
|
||
}
|
||
}
|
||
}
|
||
|
||
return $keysMissing;
|
||
}
|
||
|
||
/**
|
||
* @param string[] $keys
|
||
* @param string[]|string[][] $checkKeys
|
||
* @return string[] List of cache keys
|
||
*/
|
||
private function getRawKeysForWarmup( array $keys, array $checkKeys ) {
|
||
if ( !$keys ) {
|
||
return [];
|
||
}
|
||
|
||
$keysWarmUp = [];
|
||
// Get all the value keys to fetch...
|
||
foreach ( $keys as $key ) {
|
||
$keysWarmUp[] = self::$VALUE_KEY_PREFIX . $key;
|
||
}
|
||
// Get all the check keys to fetch...
|
||
foreach ( $checkKeys as $i => $checkKeyOrKeys ) {
|
||
if ( is_int( $i ) ) {
|
||
// Single check key that applies to all value keys
|
||
$keysWarmUp[] = self::$TIME_KEY_PREFIX . $checkKeyOrKeys;
|
||
} else {
|
||
// List of check keys that apply to value key $i
|
||
$keysWarmUp = array_merge(
|
||
$keysWarmUp,
|
||
self::prefixCacheKeys( $checkKeyOrKeys, self::$TIME_KEY_PREFIX )
|
||
);
|
||
}
|
||
}
|
||
|
||
$warmupCache = $this->cache->getMulti( $keysWarmUp );
|
||
$warmupCache += array_fill_keys( $keysWarmUp, false );
|
||
|
||
return $warmupCache;
|
||
}
|
||
|
||
/**
|
||
* @return float UNIX timestamp
|
||
* @codeCoverageIgnore
|
||
*/
|
||
protected function getCurrentTime() {
|
||
if ( $this->wallClockOverride ) {
|
||
return $this->wallClockOverride;
|
||
}
|
||
|
||
$clockTime = (float)time(); // call this first
|
||
// microtime() uses an initial gettimeofday() call added to usage clocks.
|
||
// This can severely drift from time() and the microtime() value of other threads
|
||
// due to undercounting of the amount of time elapsed. Instead of seeing the current
|
||
// time as being in the past, use the value of time(). This avoids setting cache values
|
||
// that will immediately be seen as expired and possibly cause stampedes.
|
||
return max( microtime( true ), $clockTime );
|
||
}
|
||
|
||
/**
|
||
* @param float|null &$time Mock UNIX timestamp for testing
|
||
* @codeCoverageIgnore
|
||
*/
|
||
public function setMockTime( &$time ) {
|
||
$this->wallClockOverride =& $time;
|
||
$this->cache->setMockTime( $time );
|
||
foreach ( $this->processCaches as $pCache ) {
|
||
$pCache->setMockTime( $time );
|
||
}
|
||
}
|
||
}
|