1<?php 2/** 3 * This program is free software; you can redistribute it and/or modify 4 * it under the terms of the GNU General Public License as published by 5 * the Free Software Foundation; either version 2 of the License, or 6 * (at your option) any later version. 7 * 8 * This program is distributed in the hope that it will be useful, 9 * but WITHOUT ANY WARRANTY; without even the implied warranty of 10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 11 * GNU General Public License for more details. 12 * 13 * You should have received a copy of the GNU General Public License along 14 * with this program; if not, write to the Free Software Foundation, Inc., 15 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. 16 * http://www.gnu.org/copyleft/gpl.html 17 * 18 * @file 19 * @ingroup Cache 20 */ 21 22use Liuggio\StatsdClient\Factory\StatsdDataFactoryInterface; 23use Psr\Log\LoggerAwareInterface; 24use Psr\Log\LoggerInterface; 25use Psr\Log\NullLogger; 26use Wikimedia\LightweightObjectStore\ExpirationAwareness; 27use Wikimedia\LightweightObjectStore\StorageAwareness; 28 29/** 30 * Multi-datacenter aware caching interface 31 * 32 * ### Using WANObjectCache 33 * 34 * All operations go to the local datacenter cache, except for delete(), 35 * touchCheckKey(), and resetCheckKey(), which broadcast to all datacenters. 36 * 37 * This class is intended for caching data from primary stores. 38 * If the get() method does not return a value, then the caller 39 * should query the new value and backfill the cache using set(). 40 * The preferred way to do this logic is through getWithSetCallback(). 41 * When querying the store on cache miss, the closest DB replica 42 * should be used. Try to avoid heavyweight DB master or quorum reads. 43 * 44 * To ensure consumers of the cache see new values in a timely manner, 45 * you either need to follow either the validation strategy, or the 46 * purge strategy. 47 * 48 * The validation strategy refers to the natural avoidance of stale data 49 * by one of the following means: 50 * 51 * - A) The cached value is immutable. 52 * If the consumer has access to an identifier that uniquely describes a value, 53 * cached value need not change. Instead, the key can change. This also allows 54 * all servers to access their perceived current version. This is important 55 * in context of multiple deployed versions of your application and/or cross-dc 56 * database replication, to ensure deterministic values without oscillation. 57 * - B) Validity is checked against the source after get(). 58 * This is the inverse of A. The unique identifier is embedded inside the value 59 * and validated after on retreival. If outdated, the value is recomputed. 60 * - C) The value is cached with a modest TTL (without validation). 61 * If value recomputation is reasonably performant, and the value is allowed to 62 * be stale, one should consider using TTL only – using the value's age as 63 * method of validation. 64 * 65 * The purge strategy refers to the approach whereby your application knows that 66 * source data has changed and can react by purging the relevant cache keys. 67 * As purges are expensive, this strategy should be avoided if possible. 68 * The simplest purge method is delete(). 69 * 70 * No matter which strategy you choose, callers must not rely on updates or purges 71 * being immediately visible to other servers. It should be treated similarly as 72 * one would a database replica. 73 * 74 * The need for immediate updates should be avoided. If needed, solutions must be 75 * sought outside WANObjectCache. 76 * 77 * @anchor wanobjectcache-deployment 78 * ### Deploying %WANObjectCache 79 * 80 * There are two supported ways to set up broadcasted operations: 81 * 82 * - A) Set up mcrouter as the underlying cache backend, using a memcached BagOStuff class 83 * for the 'cache' parameter. The 'broadcastRoutingPrefix' parameter must be provided. 84 * Configure mcrouter as follows: 85 * - 1) Use Route Prefixing based on region (datacenter) and cache cluster. 86 * See https://github.com/facebook/mcrouter/wiki/Routing-Prefix and 87 * https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup. 88 * - 2) To increase the consistency of delete() and touchCheckKey() during cache 89 * server membership changes, you can use the OperationSelectorRoute to 90 * configure 'set' and 'delete' operations to go to all servers in the cache 91 * cluster, instead of just one server determined by hashing. 92 * See https://github.com/facebook/mcrouter/wiki/List-of-Route-Handles. 93 * - B) Set up dynomite as a cache middleware between the web servers and either memcached 94 * or redis and use it as the underlying cache backend, using a memcached BagOStuff 95 * class for the 'cache' parameter. This will broadcast all key setting operations, 96 * not just purges, which can be useful for cache warming. Writes are eventually 97 * consistent via the Dynamo replication model. See https://github.com/Netflix/dynomite. 98 * 99 * Broadcasted operations like delete() and touchCheckKey() are intended to run 100 * immediately in the local datacenter and asynchronously in remote datacenters. 101 * 102 * This means that callers in all datacenters may see older values for however many 103 * milliseconds that the purge took to reach that datacenter. As with any cache, this 104 * should not be relied on for cases where reads are used to determine writes to source 105 * (e.g. non-cache) data stores, except when reading immutable data. 106 * 107 * All values are wrapped in metadata arrays. Keys use a "WANCache:" prefix to avoid 108 * collisions with keys that are not wrapped as metadata arrays. For any given key that 109 * a caller uses, there are several "sister" keys that might be involved under the hood. 110 * Each "sister" key differs only by a single-character: 111 * - v: used for regular value keys 112 * - i: used for temporarily storing values of tombstoned keys 113 * - t: used for storing timestamp "check" keys 114 * - m: used for temporary mutex keys to avoid cache stampedes 115 * 116 * @ingroup Cache 117 * @since 1.26 118 */ 119class WANObjectCache implements 120 ExpirationAwareness, 121 StorageAwareness, 122 IStoreKeyEncoder, 123 LoggerAwareInterface 124{ 125 /** @var BagOStuff The local datacenter cache */ 126 protected $cache; 127 /** @var MapCacheLRU[] Map of group PHP instance caches */ 128 protected $processCaches = []; 129 /** @var LoggerInterface */ 130 protected $logger; 131 /** @var StatsdDataFactoryInterface */ 132 protected $stats; 133 /** @var callable|null Function that takes a WAN cache callback and runs it later */ 134 protected $asyncHandler; 135 136 /** 137 * Routing prefix for values that should be broadcasted to all data centers. 138 * 139 * If null, then a proxy other than mcrouter handles broadcasting or there is only one datacenter. 140 * 141 * @var string|null 142 */ 143 protected $broadcastRoute; 144 /** @var string|null Routing prefix for value keys that support use of an on-host tier */ 145 protected $onHostRoute; 146 /** @var bool Whether to use "interim" caching while keys are tombstoned */ 147 protected $useInterimHoldOffCaching = true; 148 /** @var float Unix timestamp of the oldest possible valid values */ 149 protected $epoch; 150 /** @var string Stable secret used for hasing long strings into key components */ 151 protected $secret; 152 /** @var int Scheme to use for key coalescing (Hash Tags or Hash Stops) */ 153 protected $coalesceScheme; 154 155 /** @var int Reads/second assumed during a hypothetical cache write stampede for a key */ 156 private $keyHighQps; 157 /** @var float Max tolerable bytes/second to spend on a cache write stampede for a key */ 158 private $keyHighUplinkBps; 159 160 /** @var int Callback stack depth for getWithSetCallback() */ 161 private $callbackDepth = 0; 162 /** @var mixed[] Temporary warm-up cache */ 163 private $warmupCache = []; 164 /** @var int Key fetched */ 165 private $warmupKeyMisses = 0; 166 167 /** @var float|null */ 168 private $wallClockOverride; 169 170 /** Max expected seconds to pass between delete() and DB commit finishing */ 171 private const MAX_COMMIT_DELAY = 3; 172 /** Max expected seconds of combined lag from replication and view snapshots */ 173 private const MAX_READ_LAG = 7; 174 /** Seconds to tombstone keys on delete() and treat as volatile after invalidation */ 175 public const HOLDOFF_TTL = self::MAX_COMMIT_DELAY + self::MAX_READ_LAG + 1; 176 177 /** Consider regeneration if the key will expire within this many seconds */ 178 private const LOW_TTL = 30; 179 /** Max TTL, in seconds, to store keys when a data sourced is lagged */ 180 public const TTL_LAGGED = 30; 181 182 /** Expected time-till-refresh, in seconds, if the key is accessed once per second */ 183 private const HOT_TTR = 900; 184 /** Minimum key age, in seconds, for expected time-till-refresh to be considered */ 185 private const AGE_NEW = 60; 186 187 /** Idiom for getWithSetCallback() meaning "no cache stampede mutex" */ 188 private const TSE_NONE = -1; 189 190 /** Idiom for set()/getWithSetCallback() meaning "no post-expiration persistence" */ 191 public const STALE_TTL_NONE = 0; 192 /** Idiom for set()/getWithSetCallback() meaning "no post-expiration grace period" */ 193 public const GRACE_TTL_NONE = 0; 194 /** Idiom for delete()/touchCheckKey() meaning "no hold-off period" */ 195 public const HOLDOFF_TTL_NONE = 0; 196 /** Alias for HOLDOFF_TTL_NONE (b/c) (deprecated since 1.34) */ 197 public const HOLDOFF_NONE = self::HOLDOFF_TTL_NONE; 198 199 /** @var float Idiom for getWithSetCallback() meaning "no minimum required as-of timestamp" */ 200 public const MIN_TIMESTAMP_NONE = 0.0; 201 202 /** Default process cache name and max key count */ 203 private const PC_PRIMARY = 'primary:1000'; 204 205 /** Idiom for get()/getMulti() to return extra information by reference */ 206 public const PASS_BY_REF = []; 207 208 /** Use twemproxy-style Hash Tag key scheme (e.g. "{...}") */ 209 private const SCHEME_HASH_TAG = 1; 210 /** Use mcrouter-style Hash Stop key scheme (e.g. "...|#|") */ 211 private const SCHEME_HASH_STOP = 2; 212 213 /** Seconds to keep dependency purge keys around */ 214 private const CHECK_KEY_TTL = self::TTL_YEAR; 215 /** Seconds to keep interim value keys for tombstoned keys around */ 216 private const INTERIM_KEY_TTL = 1; 217 218 /** Seconds to keep lock keys around */ 219 private const LOCK_TTL = 10; 220 /** Seconds to no-op key set() calls to avoid large blob I/O stampedes */ 221 private const COOLOFF_TTL = 1; 222 /** Seconds to ramp up the chance of regeneration due to expected time-till-refresh */ 223 private const RAMPUP_TTL = 30; 224 225 /** @var float Tiny negative float to use when CTL comes up >= 0 due to clock skew */ 226 private const TINY_NEGATIVE = -0.000001; 227 /** @var float Tiny positive float to use when using "minTime" to assert an inequality */ 228 private const TINY_POSTIVE = 0.000001; 229 230 /** Min millisecond set() backoff during hold-off (far less than INTERIM_KEY_TTL) */ 231 private const RECENT_SET_LOW_MS = 50; 232 /** Max millisecond set() backoff during hold-off (far less than INTERIM_KEY_TTL) */ 233 private const RECENT_SET_HIGH_MS = 100; 234 235 /** Consider value generation slow if it takes more than this many seconds */ 236 private const GENERATION_SLOW_SEC = 3; 237 238 /** Key to the tombstone entry timestamp */ 239 private const PURGE_TIME = 0; 240 /** Key to the tombstone entry hold-off TTL */ 241 private const PURGE_HOLDOFF = 1; 242 243 /** Cache format version number */ 244 private const VERSION = 1; 245 246 /** The key value component of a fetchMulti() result */ 247 private const RES_VALUE = 0; 248 /** The key metadata component of a fetchMulti() result */ 249 private const RES_METADATA = 1; 250 251 /** Version number attribute for a key; keep value for b/c (< 1.36) */ 252 public const KEY_VERSION = 'version'; 253 /** Generation timestamp attribute for a key; keep value for b/c (< 1.36) */ 254 public const KEY_AS_OF = 'asOf'; 255 /** Logical TTL attribute for a key */ 256 public const KEY_TTL = 'ttl'; 257 /** Remaining TTL attribute for a key; keep value for b/c (< 1.36) */ 258 public const KEY_CUR_TTL = 'curTTL'; 259 /** Tomstone timestamp attribute for a key; keep value for b/c (< 1.36) */ 260 public const KEY_TOMB_AS_OF = 'tombAsOf'; 261 /** Highest "check" key timestamp for a key; keep value for b/c (< 1.36) */ 262 public const KEY_CHECK_AS_OF = 'lastCKPurge'; 263 264 /** Key to WAN cache version number */ 265 private const FLD_FORMAT_VERSION = 0; 266 /** Key to the cached value */ 267 private const FLD_VALUE = 1; 268 /** Key to the original TTL */ 269 private const FLD_TTL = 2; 270 /** Key to the cache timestamp */ 271 private const FLD_TIME = 3; 272 /** Key to the flags bit field (reserved number) */ 273 private const /** @noinspection PhpUnusedPrivateFieldInspection */ FLD_FLAGS = 4; 274 /** Key to collection cache version number */ 275 private const FLD_VALUE_VERSION = 5; 276 /** Key to how long it took to generate the value */ 277 private const FLD_GENERATION_TIME = 6; 278 279 /** Single character value mutex key component */ 280 private const TYPE_VALUE = 'v'; 281 /** Single character timestamp key component */ 282 private const TYPE_TIMESTAMP = 't'; 283 /** Single character flux key component */ 284 private const TYPE_FLUX = 'f'; 285 /** Single character mutex key component */ 286 private const TYPE_MUTEX = 'm'; 287 /** Single character interium key component */ 288 private const TYPE_INTERIM = 'i'; 289 /** Single character cool-off key component */ 290 private const TYPE_COOLOFF = 'c'; 291 292 /** Prefix for tombstone key values */ 293 private const PURGE_VAL_PREFIX = 'PURGED:'; 294 295 /** 296 * @param array $params 297 * - cache : BagOStuff object for a persistent cache 298 * - logger : LoggerInterface object 299 * - stats : StatsdDataFactoryInterface object 300 * - asyncHandler : A function that takes a callback and runs it later. If supplied, 301 * whenever a preemptive refresh would be triggered in getWithSetCallback(), the 302 * current cache value is still used instead. However, the async-handler function 303 * receives a WAN cache callback that, when run, will execute the value generation 304 * callback supplied by the getWithSetCallback() caller. The result will be saved 305 * as normal. The handler is expected to call the WAN cache callback at an opportune 306 * time (e.g. HTTP post-send), though generally within a few 100ms. [optional] 307 * - broadcastRoutingPrefix: a routing prefix used to broadcast "set" and "delete" operations to all 308 * datacenters; See also https://github.com/facebook/mcrouter/wiki/Config-Files for background 309 * on this. 310 * This prefix takes the form `/<datacenter>/<name of wan route>/` where `datacenter` should 311 * generally be a wildcard, to select all matching routes (e.g. the WAN cluster in all DCs) 312 * See also <https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup>. 313 * This is required when using mcrouter as the backing store proxy. [optional] 314 * - onHostRoutingPrefix: a routing prefix that considers a server-local cache ("on-host tier") 315 * for "value" keys before reading from the main cache cluster in the current data center. 316 * The "helper" keys will still be read from the main cache cluster. An on-host tier can help 317 * reduce network saturation due to large value transfers yet without needing to explicitly 318 * know, opt-in, or measure which values are large. 319 * The on-host tier may blindy store and serve values from the main cluster for up to 10 320 * seconds (must be less than WANObjectCache::HOLDOFF_TTL, as otherwise WANObjectCache will 321 * be unable to apply purges from the main cluster, which don't live longer than that). 322 * This prefix takes the form `/<datacenter>/<name of onhost route>/` where `datacenter` 323 * may be a wildcard. This can be used with mcrouter. [optional] 324 * - epoch: lowest UNIX timestamp a value/tombstone must have to be valid. [optional] 325 * - secret: stable secret used for hashing long strings into key components. [optional] 326 * - coalesceScheme: which key scheme to use in order to encourage the backend to place any 327 * "helper" keys for a "value" key within the same cache server. This reduces network 328 * overhead and reduces the chance the a single downed cache server causes disruption. 329 * Use "hash_stop" with mcrouter and "hash_tag" with dynomite. [default: "hash_stop"] 330 * - keyHighQps: reads/second assumed during a hypothetical cache write stampede for 331 * a single key. This is used to decide when the overhead of checking short-lived 332 * write throttling keys is worth it. 333 * [default: 100] 334 * - keyHighUplinkBps: maximum tolerable bytes/second to spend on a cache write stampede 335 * for a single key. This is used to decide when the overhead of checking short-lived 336 * write throttling keys is worth it. [default: (1/100 of a 1Gbps link)] 337 */ 338 public function __construct( array $params ) { 339 $this->cache = $params['cache']; 340 $this->broadcastRoute = $params['broadcastRoutingPrefix'] ?? null; 341 $this->onHostRoute = $params['onHostRoutingPrefix'] ?? null; 342 $this->epoch = $params['epoch'] ?? 0; 343 $this->secret = $params['secret'] ?? (string)$this->epoch; 344 if ( ( $params['coalesceScheme'] ?? '' ) === 'hash_tag' ) { 345 // https://redis.io/topics/cluster-spec 346 // https://github.com/twitter/twemproxy/blob/v0.4.1/notes/recommendation.md#hash-tags 347 // https://github.com/Netflix/dynomite/blob/v0.7.0/notes/recommendation.md#hash-tags 348 $this->coalesceScheme = self::SCHEME_HASH_TAG; 349 } else { 350 // https://github.com/facebook/mcrouter/wiki/Key-syntax 351 $this->coalesceScheme = self::SCHEME_HASH_STOP; 352 } 353 354 $this->keyHighQps = $params['keyHighQps'] ?? 100; 355 $this->keyHighUplinkBps = $params['keyHighUplinkBps'] ?? ( 1e9 / 8 / 100 ); 356 357 $this->setLogger( $params['logger'] ?? new NullLogger() ); 358 $this->stats = $params['stats'] ?? new NullStatsdDataFactory(); 359 $this->asyncHandler = $params['asyncHandler'] ?? null; 360 361 $this->cache->registerWrapperInfoForStats( 362 'WANCache', 363 'wanobjectcache', 364 [ __CLASS__, 'getCollectionFromSisterKey' ] 365 ); 366 } 367 368 /** 369 * @param LoggerInterface $logger 370 */ 371 public function setLogger( LoggerInterface $logger ) { 372 $this->logger = $logger; 373 } 374 375 /** 376 * Get an instance that wraps EmptyBagOStuff 377 * 378 * @return WANObjectCache 379 */ 380 public static function newEmpty() { 381 return new static( [ 'cache' => new EmptyBagOStuff() ] ); 382 } 383 384 /** 385 * Fetch the value of a key from cache 386 * 387 * If supplied, $curTTL is set to the remaining TTL (current time left): 388 * - a) INF; if $key exists, has no TTL, and is not invalidated by $checkKeys 389 * - b) float (>=0); if $key exists, has a TTL, and is not invalidated by $checkKeys 390 * - c) float (<0); if $key is tombstoned, stale, or existing but invalidated by $checkKeys 391 * - d) null; if $key does not exist and is not tombstoned 392 * 393 * If a key is tombstoned, $curTTL will reflect the time since delete(). 394 * 395 * The timestamp of $key will be checked against the last-purge timestamp 396 * of each of $checkKeys. Those $checkKeys not in cache will have the last-purge 397 * initialized to the current timestamp. If any of $checkKeys have a timestamp 398 * greater than that of $key, then $curTTL will reflect how long ago $key 399 * became invalid. Callers can use $curTTL to know when the value is stale. 400 * The $checkKeys parameter allow mass invalidations by updating a single key: 401 * - a) Each "check" key represents "last purged" of some source data 402 * - b) Callers pass in relevant "check" keys as $checkKeys in get() 403 * - c) When the source data that "check" keys represent changes, 404 * the touchCheckKey() method is called on them 405 * 406 * Source data entities might exists in a DB that uses snapshot isolation 407 * (e.g. the default REPEATABLE-READ in innoDB). Even for mutable data, that 408 * isolation can largely be maintained by doing the following: 409 * - a) Calling delete() on entity change *and* creation, before DB commit 410 * - b) Keeping transaction duration shorter than the delete() hold-off TTL 411 * - c) Disabling interim key caching via useInterimHoldOffCaching() before get() calls 412 * 413 * However, pre-snapshot values might still be seen if an update was made 414 * in a remote datacenter but the purge from delete() didn't relay yet. 415 * 416 * Consider using getWithSetCallback(), which has cache slam avoidance and key 417 * versioning features, instead of bare get()/set() calls. 418 * 419 * Do not use this method on versioned keys accessed via getWithSetCallback(). 420 * 421 * When using the $info parameter, it should be passed in as WANObjectCache::PASS_BY_REF. 422 * In that case, it becomes a key metadata map. Otherwise, for backwards compatibility, 423 * $info becomes the value generation timestamp (null if the key is nonexistant/tombstoned). 424 * Key metadata map fields include: 425 * - WANObjectCache::KEY_VERSION: value version number; null if key is nonexistant 426 * - WANObjectCache::KEY_AS_OF: value generation timestamp (UNIX); null if key is nonexistant 427 * - WANObjectCache::KEY_TTL: assigned TTL (seconds); null if key is nonexistant/tombstoned 428 * - WANObjectCache::KEY_CUR_TTL: remaining TTL (seconds); null if key is nonexistant 429 * - WANObjectCache::KEY_TOMB_AS_OF: tombstone timestamp (UNIX); null if key is not tombstoned 430 * - WANObjectCache::KEY_CHECK_AS_OF: highest "check" key timestamp (UNIX); null if none 431 * 432 * @param string $key Cache key made with makeKey()/makeGlobalKey() 433 * @param float|null &$curTTL Seconds of TTL left [returned] 434 * @param string[] $checkKeys Map of (integer or cache key => "check" key(s)); 435 * "check" keys must also be made with makeKey()/makeGlobalKey() 436 * @param array &$info Metadata map [returned] 437 * @return mixed Value of cache key; false on failure 438 */ 439 final public function get( $key, &$curTTL = null, array $checkKeys = [], &$info = [] ) { 440 // Note that an undeclared variable passed as $info starts as null (not the default). 441 // Also, if no $info parameter is provided, then it doesn't matter how it changes here. 442 $legacyInfo = ( $info !== self::PASS_BY_REF ); 443 444 $res = $this->fetchKeys( [ $key ], $checkKeys )[$key]; 445 $value = $res[self::RES_VALUE]; 446 $metadata = $res[self::RES_METADATA]; 447 448 $curTTL = $metadata[self::KEY_CUR_TTL]; 449 $info = $legacyInfo ? $metadata[self::KEY_AS_OF] : $metadata; 450 451 return $value; 452 } 453 454 /** 455 * Fetch the value of several keys from cache 456 * 457 * $curTTLs becomes a map of only present/tombstoned $keys to their current time-to-live. 458 * 459 * $checkKeys holds the "check" keys used to validate values of applicable keys. The 460 * integer indexes hold "check" keys that apply to all of $keys while the string indexes 461 * hold "check" keys that only apply to the cache key with that name. The logic of "check" 462 * keys otherwise works the same as in WANObjectCache::get(). 463 * 464 * When using the $info parameter, it should be passed in as WANObjectCache::PASS_BY_REF. 465 * In that case, it becomes a mapping of all the $keys to their metadata maps, each in the 466 * style of WANObjectCache::get(). Otherwise, for backwards compatibility, $info becomes a 467 * map of only present/tombstoned $keys to their value generation timestamps. 468 * 469 * @see WANObjectCache::get() 470 * 471 * @param string[] $keys List/map with makeKey()/makeGlobalKey() cache keys as values 472 * @param array<string,float> &$curTTLs Map of (key => seconds of TTL left) [returned] 473 * @param string[]|string[][] $checkKeys Map of (integer or cache key => "check" key(s)); 474 * "check" keys must also be made with makeKey()/makeGlobalKey() 475 * @param array<string,array> &$info Map of (key => metadata map) [returned] 476 * @return array<string,mixed> Map of (key => value) for existing values in order of $keys 477 */ 478 final public function getMulti( 479 array $keys, 480 &$curTTLs = [], 481 array $checkKeys = [], 482 &$info = [] 483 ) { 484 // Note that an undeclared variable passed as $info starts as null (not the default). 485 // Also, if no $info parameter is provided, then it doesn't matter how it changes here. 486 $legacyInfo = ( $info !== self::PASS_BY_REF ); 487 488 $curTTLs = []; 489 $info = []; 490 $valuesByKey = []; 491 492 $resByKey = $this->fetchKeys( $keys, $checkKeys ); 493 foreach ( $resByKey as $key => $res ) { 494 $value = $res[self::RES_VALUE]; 495 $metadata = $res[self::RES_METADATA]; 496 497 if ( $value !== false ) { 498 $valuesByKey[$key] = $value; 499 } 500 501 if ( $metadata[self::KEY_CUR_TTL] !== null ) { 502 $curTTLs[$key] = $metadata[self::KEY_CUR_TTL]; 503 } 504 505 $info[$key] = $legacyInfo ? $metadata[self::KEY_AS_OF] : $metadata; 506 } 507 508 return $valuesByKey; 509 } 510 511 /** 512 * Fetch the value and key metadata of several keys from cache 513 * 514 * $checkKeys holds the "check" keys used to validate values of applicable keys. 515 * The integer indexes hold "check" keys that apply to all of $keys while the string 516 * indexes hold "check" keys that only apply to the cache key with that name. 517 * 518 * This returns a map of (key => result map), with entries for each key in $key. 519 * Result maps include the following fields: 520 * - WANObjectCache::RESULT_VALUE: the value; false if tombstoned/nonexistent 521 * - WANObjectCache::RESULT_ATTRIBUTES: the WANObjectCache::KEY_* metadata map 522 * 523 * @param string[] $keys List/map with makeKey()/makeGlobalKey() cache keys as values 524 * @param string[]|string[][] $checkKeys Map of (integer or cache key => "check" key(s)); 525 * "check" keys must also be made with makeKey()/makeGlobalKey() 526 * @return array<string,array{0:mixed,1:array}> Map of (key => result map) in order of $keys 527 */ 528 protected function fetchKeys( array $keys, array $checkKeys ) { 529 $resByKey = []; 530 531 // List of all sister keys that need to be fetched from cache 532 $allSisterKeys = []; 533 // Order-corresponding value sister key list for the base key list ($keys) 534 $valueSisterKeys = []; 535 // Order-corresponding "flux" sister key list for the base key list ($keys) or [] 536 $fluxSisterKeys = []; 537 // List of "check" sister keys to compare all value sister keys against 538 $checkSisterKeysForAll = []; 539 // Map of (base key => additional "check" sister key(s) to compare against) 540 $checkSisterKeysByKey = []; 541 542 foreach ( $keys as $key ) { 543 $sisterKey = $this->makeSisterKey( $key, self::TYPE_VALUE, $this->onHostRoute ); 544 $allSisterKeys[] = $sisterKey; 545 $valueSisterKeys[] = $sisterKey; 546 if ( $this->onHostRoute !== null ) { 547 $sisterKey = $this->makeSisterKey( $key, self::TYPE_FLUX ); 548 $allSisterKeys[] = $sisterKey; 549 $fluxSisterKeys[] = $sisterKey; 550 } 551 } 552 553 foreach ( $checkKeys as $i => $checkKeyOrKeyGroup ) { 554 // Note: avoid array_merge() inside loop in case there are many keys 555 if ( is_int( $i ) ) { 556 // Single "check" key that applies to all base keys 557 $sisterKey = $this->makeSisterKey( $checkKeyOrKeyGroup, self::TYPE_TIMESTAMP ); 558 $allSisterKeys[] = $sisterKey; 559 $checkSisterKeysForAll[] = $sisterKey; 560 } else { 561 // List of "check" keys that apply to a specific base key 562 foreach ( (array)$checkKeyOrKeyGroup as $checkKey ) { 563 $sisterKey = $this->makeSisterKey( $checkKey, self::TYPE_TIMESTAMP ); 564 $allSisterKeys[] = $sisterKey; 565 $checkSisterKeysByKey[$i][] = $sisterKey; 566 } 567 } 568 } 569 570 if ( $this->warmupCache ) { 571 // Get the wrapped values of the sister keys from the warmup cache 572 $wrappedBySisterKey = $this->warmupCache; 573 $sisterKeysMissing = array_diff( $allSisterKeys, array_keys( $wrappedBySisterKey ) ); 574 if ( $sisterKeysMissing ) { // sanity 575 $this->warmupKeyMisses += count( $sisterKeysMissing ); 576 $wrappedBySisterKey += $this->cache->getMulti( $sisterKeysMissing ); 577 } 578 } else { 579 // Fetch the wrapped values of the sister keys from the backend 580 $wrappedBySisterKey = $this->cache->getMulti( $allSisterKeys ); 581 } 582 583 // Pessimistically treat the "current time" as the time when any network I/O finished 584 $now = $this->getCurrentTime(); 585 586 // List of "check" sister key purge timestamps to compare all value sister keys against 587 $ckPurgesForAll = $this->processCheckKeys( 588 $checkSisterKeysForAll, 589 $wrappedBySisterKey, 590 $now 591 ); 592 // Map of (base key => extra "check" sister key purge timestamp(s) to compare against) 593 $ckPurgesByKey = []; 594 foreach ( $checkSisterKeysByKey as $keyWithCheckKeys => $checkKeysForKey ) { 595 $ckPurgesByKey[$keyWithCheckKeys] = $this->processCheckKeys( 596 $checkKeysForKey, 597 $wrappedBySisterKey, 598 $now 599 ); 600 } 601 602 // Map of (base key => "flux" key purge timestamp to compare against) 603 $fkPurgesByKey = $this->processFluxKeys( $keys, $fluxSisterKeys, $wrappedBySisterKey ); 604 605 // Unwrap and validate any value found for each base key (under the value sister key) 606 reset( $keys ); 607 foreach ( $valueSisterKeys as $valueSisterKey ) { 608 // Get the corresponding base key for this value sister key 609 $key = current( $keys ); 610 next( $keys ); 611 612 if ( isset( $fkPurgesByKey[$key] ) ) { 613 // An on-host tier is in use and a "flux" sister key exists for this 614 // Treat the value sister key as if it was a tombstone with this value. 615 $wrapped = $fkPurgesByKey[$key]; 616 } elseif ( array_key_exists( $valueSisterKey, $wrappedBySisterKey ) ) { 617 // Key exists as either a live value or tombstone value 618 $wrapped = $wrappedBySisterKey[$valueSisterKey]; 619 } else { 620 // Key does not exist 621 $wrapped = false; 622 } 623 624 list( $value, $metadata ) = $this->unwrap( $wrapped, $now ); 625 // Include the timestamp of the newest "check" key purge/initialization 626 $metadata[self::KEY_CHECK_AS_OF] = null; 627 628 foreach ( array_merge( $ckPurgesForAll, $ckPurgesByKey[$key] ?? [] ) as $ckPurge ) { 629 $metadata[self::KEY_CHECK_AS_OF] = max( 630 $ckPurge[self::PURGE_TIME], 631 $metadata[self::KEY_CHECK_AS_OF] 632 ); 633 // Timestamp marking the end of the hold-off period for this purge 634 $holdoffDeadline = $ckPurge[self::PURGE_TIME] + $ckPurge[self::PURGE_HOLDOFF]; 635 // Check if the value was generated during the hold-off period 636 if ( $value !== false && $holdoffDeadline >= $metadata[self::KEY_AS_OF] ) { 637 // How long ago this value was invalidated by *this* "check" key 638 $ago = min( $ckPurge[self::PURGE_TIME] - $now, self::TINY_NEGATIVE ); 639 // How long ago this value was invalidated by *any* known "check" key 640 $metadata[self::KEY_CUR_TTL] = min( $metadata[self::KEY_CUR_TTL], $ago ); 641 } 642 } 643 644 $resByKey[$key] = [ self::RES_VALUE => $value, self::RES_METADATA => $metadata ]; 645 } 646 647 return $resByKey; 648 } 649 650 /** 651 * @param string[] $keys Base key list 652 * @param string[] $fluxSisterKeys Order-corresponding "flux" key list for base keys or [] 653 * @param mixed[] $wrappedBySisterKey Preloaded map of (sister key => wrapped value) 654 * @return array[] List of purge value arrays 655 */ 656 private function processFluxKeys( 657 array $keys, 658 array $fluxSisterKeys, 659 array $wrappedBySisterKey 660 ) { 661 $purges = []; 662 663 reset( $keys ); 664 foreach ( $fluxSisterKeys as $fluxKey ) { 665 // Get the corresponding base key for this "flux" key 666 $key = current( $keys ); 667 next( $keys ); 668 669 $purge = isset( $wrappedBySisterKey[$fluxKey] ) 670 ? $this->parsePurgeValue( $wrappedBySisterKey[$fluxKey] ) 671 : false; 672 673 if ( $purge !== false ) { 674 $purges[$key] = $purge; 675 } 676 } 677 678 return $purges; 679 } 680 681 /** 682 * @param string[] $checkSisterKeys List of "check" sister keys 683 * @param mixed[] $wrappedBySisterKey Preloaded map of (sister key => wrapped value) 684 * @param float $now UNIX timestamp 685 * @return array[] List of purge value arrays 686 */ 687 private function processCheckKeys( 688 array $checkSisterKeys, 689 array $wrappedBySisterKey, 690 float $now 691 ) { 692 $purges = []; 693 694 foreach ( $checkSisterKeys as $timeKey ) { 695 $purge = isset( $wrappedBySisterKey[$timeKey] ) 696 ? $this->parsePurgeValue( $wrappedBySisterKey[$timeKey] ) 697 : false; 698 699 if ( $purge === false ) { 700 // Key is not set or malformed; regenerate 701 $newVal = $this->makeCheckPurgeValue( $now, self::HOLDOFF_TTL ); 702 $this->cache->add( $timeKey, $newVal, self::CHECK_KEY_TTL ); 703 $purge = $this->parsePurgeValue( $newVal ); 704 } 705 706 $purges[] = $purge; 707 } 708 709 return $purges; 710 } 711 712 /** 713 * Set the value of a key in cache 714 * 715 * Simply calling this method when source data changes is not valid because 716 * the changes do not replicate to the other WAN sites. In that case, delete() 717 * should be used instead. This method is intended for use on cache misses. 718 * 719 * If the data was read from a snapshot-isolated transactions (e.g. the default 720 * REPEATABLE-READ in innoDB), use 'since' to avoid the following race condition: 721 * - a) T1 starts 722 * - b) T2 updates a row, calls delete(), and commits 723 * - c) The HOLDOFF_TTL passes, expiring the delete() tombstone 724 * - d) T1 reads the row and calls set() due to a cache miss 725 * - e) Stale value is stuck in cache 726 * 727 * Setting 'lag' and 'since' help avoids keys getting stuck in stale states. 728 * 729 * Be aware that this does not update the process cache for getWithSetCallback() 730 * callers. Keys accessed via that method are not generally meant to also be set 731 * using this primitive method. 732 * 733 * Consider using getWithSetCallback(), which has cache slam avoidance and key 734 * versioning features, instead of bare get()/set() calls. 735 * 736 * Do not use this method on versioned keys accessed via getWithSetCallback(). 737 * 738 * Example usage: 739 * @code 740 * $dbr = wfGetDB( DB_REPLICA ); 741 * $setOpts = Database::getCacheSetOptions( $dbr ); 742 * // Fetch the row from the DB 743 * $row = $dbr->selectRow( ... ); 744 * $key = $cache->makeKey( 'building', $buildingId ); 745 * $cache->set( $key, $row, $cache::TTL_DAY, $setOpts ); 746 * @endcode 747 * 748 * @param string $key Cache key made with makeKey()/makeGlobalKey() 749 * @param mixed $value 750 * @param int $ttl Seconds to live. Special values are: 751 * - WANObjectCache::TTL_INDEFINITE: Cache forever (default) 752 * - WANObjectCache::TTL_UNCACHEABLE: Do not cache (if the key exists, it is not deleted) 753 * @param array $opts Options map: 754 * - lag: Seconds of replica DB lag. Typically, this is either the replica DB lag 755 * before the data was read or, if applicable, the replica DB lag before 756 * the snapshot-isolated transaction the data was read from started. 757 * Use false to indicate that replication is not running. 758 * Default: 0 seconds 759 * - since: UNIX timestamp of the data in $value. Typically, this is either 760 * the current time the data was read or (if applicable) the time when 761 * the snapshot-isolated transaction the data was read from started. 762 * Default: 0 seconds 763 * - pending: Whether this data is possibly from an uncommitted write transaction. 764 * Generally, other threads should not see values from the future and 765 * they certainly should not see ones that ended up getting rolled back. 766 * Default: false 767 * - lockTSE: If excessive replication/snapshot lag is detected, then store the value 768 * with this TTL and flag it as stale. This is only useful if the reads for this key 769 * use getWithSetCallback() with "lockTSE" set. Note that if "staleTTL" is set 770 * then it will still add on to this TTL in the excessive lag scenario. 771 * Default: WANObjectCache::TSE_NONE 772 * - staleTTL: Seconds to keep the key around if it is stale. The get()/getMulti() 773 * methods return such stale values with a $curTTL of 0, and getWithSetCallback() 774 * will call the regeneration callback in such cases, passing in the old value 775 * and its as-of time to the callback. This is useful if adaptiveTTL() is used 776 * on the old value's as-of time when it is verified as still being correct. 777 * Default: WANObjectCache::STALE_TTL_NONE 778 * - creating: Optimize for the case where the key does not already exist. 779 * Default: false 780 * - version: Integer version number signifiying the format of the value. 781 * Default: null 782 * - walltime: How long the value took to generate in seconds. Default: null 783 * @phpcs:ignore Generic.Files.LineLength 784 * @phan-param array{lag?:int,since?:int,pending?:bool,lockTSE?:int,staleTTL?:int,creating?:bool,version?:int,walltime?:int|float} $opts 785 * @note Options added in 1.28: staleTTL 786 * @note Options added in 1.33: creating 787 * @note Options added in 1.34: version, walltime 788 * @return bool Success 789 */ 790 final public function set( $key, $value, $ttl = self::TTL_INDEFINITE, array $opts = [] ) { 791 $now = $this->getCurrentTime(); 792 $lag = $opts['lag'] ?? 0; 793 $age = isset( $opts['since'] ) ? max( 0, $now - $opts['since'] ) : 0; 794 $pending = $opts['pending'] ?? false; 795 $lockTSE = $opts['lockTSE'] ?? self::TSE_NONE; 796 $staleTTL = $opts['staleTTL'] ?? self::STALE_TTL_NONE; 797 $creating = $opts['creating'] ?? false; 798 $version = $opts['version'] ?? null; 799 $walltime = $opts['walltime'] ?? null; 800 801 if ( $ttl < 0 ) { 802 return true; // not cacheable 803 } 804 805 // Do not cache potentially uncommitted data as it might get rolled back 806 if ( $pending ) { 807 $this->logger->info( 808 'Rejected set() for {cachekey} due to pending writes.', 809 [ 'cachekey' => $key ] 810 ); 811 812 return true; // no-op the write for being unsafe 813 } 814 815 // Check if there is a risk of caching (stale) data that predates the last delete() 816 // tombstone due to the tombstone having expired. If so, then the behavior should depend 817 // on whether the problem is specific to this regeneration attempt or systemically affects 818 // attempts to regenerate this key. For systemic cases, the cache writes should set a low 819 // TTL so that the value at least remains cacheable. For non-systemic cases, the cache 820 // write can simply be rejected. 821 if ( $age > self::MAX_READ_LAG ) { 822 // Case A: high snapshot lag 823 if ( $walltime === null ) { 824 // Case A0: high snapshot lag without regeneration wall time info. 825 // Probably systemic; use a low TTL to avoid stampedes/uncacheability. 826 $mitigated = 'snapshot lag'; 827 $mitigationTTL = self::TTL_SECOND; 828 } elseif ( ( $age - $walltime ) > self::MAX_READ_LAG ) { 829 // Case A1: value regeneration during an already long-running transaction. 830 // Probably non-systemic; rely on a less problematic regeneration attempt. 831 $mitigated = 'snapshot lag (late regeneration)'; 832 $mitigationTTL = self::TTL_UNCACHEABLE; 833 } else { 834 // Case A2: value regeneration takes a long time. 835 // Probably systemic; use a low TTL to avoid stampedes/uncacheability. 836 $mitigated = 'snapshot lag (high regeneration time)'; 837 $mitigationTTL = self::TTL_SECOND; 838 } 839 } elseif ( $lag === false || $lag > self::MAX_READ_LAG ) { 840 // Case B: high replication lag without high snapshot lag 841 // Probably systemic; use a low TTL to avoid stampedes/uncacheability 842 $mitigated = 'replication lag'; 843 $mitigationTTL = self::TTL_LAGGED; 844 } elseif ( ( $lag + $age ) > self::MAX_READ_LAG ) { 845 // Case C: medium length request with medium replication lag 846 // Probably non-systemic; rely on a less problematic regeneration attempt 847 $mitigated = 'read lag'; 848 $mitigationTTL = self::TTL_UNCACHEABLE; 849 } else { 850 // New value generated with recent enough data 851 $mitigated = null; 852 $mitigationTTL = null; 853 } 854 855 if ( $mitigationTTL === self::TTL_UNCACHEABLE ) { 856 $this->logger->warning( 857 "Rejected set() for {cachekey} due to $mitigated.", 858 [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age, 'walltime' => $walltime ] 859 ); 860 861 return true; // no-op the write for being unsafe 862 } 863 864 // TTL to use in staleness checks (does not effect persistence layer TTL) 865 $logicalTTL = null; 866 867 if ( $mitigationTTL !== null ) { 868 // New value generated from data that is old enough to be risky 869 if ( $lockTSE >= 0 ) { 870 // Value will have the normal expiry but will be seen as stale sooner 871 $logicalTTL = min( $ttl ?: INF, $mitigationTTL ); 872 } else { 873 // Value expires sooner (leaving enough TTL for preemptive refresh) 874 $ttl = min( $ttl ?: INF, max( $mitigationTTL, self::LOW_TTL ) ); 875 } 876 877 $this->logger->warning( 878 "Lowered set() TTL for {cachekey} due to $mitigated.", 879 [ 'cachekey' => $key, 'lag' => $lag, 'age' => $age, 'walltime' => $walltime ] 880 ); 881 } 882 883 // Wrap that value with time/TTL/version metadata 884 $wrapped = $this->wrap( $value, $logicalTTL ?: $ttl, $version, $now, $walltime ); 885 $storeTTL = $ttl + $staleTTL; 886 887 if ( $creating ) { 888 $ok = $this->cache->add( 889 $this->makeSisterKey( $key, self::TYPE_VALUE ), 890 $wrapped, 891 $storeTTL 892 ); 893 } else { 894 $ok = $this->cache->merge( 895 $this->makeSisterKey( $key, self::TYPE_VALUE ), 896 static function ( $cache, $key, $cWrapped ) use ( $wrapped ) { 897 // A string value means that it is a tombstone; do nothing in that case 898 return ( is_string( $cWrapped ) ) ? false : $wrapped; 899 }, 900 $storeTTL, 901 1 // 1 attempt 902 ); 903 } 904 905 return $ok; 906 } 907 908 /** 909 * Purge a key from all datacenters 910 * 911 * This should only be called when the underlying data (being cached) 912 * changes in a significant way. This deletes the key and starts a hold-off 913 * period where the key cannot be written to for a few seconds (HOLDOFF_TTL). 914 * This is done to avoid the following race condition: 915 * - a) Some DB data changes and delete() is called on a corresponding key 916 * - b) A request refills the key with a stale value from a lagged DB 917 * - c) The stale value is stuck there until the key is expired/evicted 918 * 919 * This is implemented by storing a special "tombstone" value at the cache 920 * key that this class recognizes; get() calls will return false for the key 921 * and any set() calls will refuse to replace tombstone values at the key. 922 * For this to always avoid stale value writes, the following must hold: 923 * - a) Replication lag is bounded to being less than HOLDOFF_TTL; or 924 * - b) If lag is higher, the DB will have gone into read-only mode already 925 * 926 * Note that set() can also be lag-aware and lower the TTL if it's high. 927 * 928 * Be aware that this does not clear the process cache. Even if it did, callbacks 929 * used by getWithSetCallback() might still return stale data in the case of either 930 * uncommitted or not-yet-replicated changes (callback generally use replica DBs). 931 * 932 * When using potentially long-running ACID transactions, a good pattern is 933 * to use a pre-commit hook to issue the delete. This means that immediately 934 * after commit, callers will see the tombstone in cache upon purge relay. 935 * It also avoids the following race condition: 936 * - a) T1 begins, changes a row, and calls delete() 937 * - b) The HOLDOFF_TTL passes, expiring the delete() tombstone 938 * - c) T2 starts, reads the row and calls set() due to a cache miss 939 * - d) T1 finally commits 940 * - e) Stale value is stuck in cache 941 * 942 * Example usage: 943 * @code 944 * $dbw->startAtomic( __METHOD__ ); // start of request 945 * ... <execute some stuff> ... 946 * // Update the row in the DB 947 * $dbw->update( ... ); 948 * $key = $cache->makeKey( 'homes', $homeId ); 949 * // Purge the corresponding cache entry just before committing 950 * $dbw->onTransactionPreCommitOrIdle( function() use ( $cache, $key ) { 951 * $cache->delete( $key ); 952 * } ); 953 * ... <execute some stuff> ... 954 * $dbw->endAtomic( __METHOD__ ); // end of request 955 * @endcode 956 * 957 * The $ttl parameter can be used when purging values that have not actually changed 958 * recently. For example, user-requested purges or cache cleanup scripts might not need 959 * to invoke a hold-off period on cache backfills, so they can use HOLDOFF_TTL_NONE. 960 * 961 * Note that $ttl limits the effective range of 'lockTSE' for getWithSetCallback(). 962 * 963 * If called twice on the same key, then the last hold-off TTL takes precedence. For 964 * idempotence, the $ttl should not vary for different delete() calls on the same key. 965 * 966 * @param string $key Cache key made with makeKey()/makeGlobalKey() 967 * @param int $ttl Tombstone TTL; Default: WANObjectCache::HOLDOFF_TTL 968 * @return bool True if the item was purged or not found, false on failure 969 */ 970 final public function delete( $key, $ttl = self::HOLDOFF_TTL ) { 971 // Purge values must be stored under the value key so that WANObjectCache::set() 972 // can atomically merge values without accidentally undoing a recent purge and thus 973 // violating the holdoff TTL restriction. 974 $valueSisterKey = $this->makeSisterKey( $key, self::TYPE_VALUE ); 975 976 // When an on-host tier is configured, fetchKeys() relies on "flux" keys to determine 977 // whether a value from the on-host tier is still valid. A "flux" key is a short-lived 978 // key that contains the last recent purge due to delete(). This approach avoids having 979 // to purge the on-host cache service on potentially hundreds of application servers. 980 981 if ( $ttl <= 0 ) { 982 // A client or cache cleanup script is requesting a cache purge, so there is no 983 // volatility period due to replica DB lag. Any recent change to an entity cached 984 // in this key should have triggered an appropriate purge event. 985 986 // Remove the key from all datacenters, ignoring any on-host tier. Since on-host 987 // tier caches only use low key TTLs, setting "flux" keys here has little practical 988 // benefit; missed purges should be rare and the on-host tier will quickly correct 989 // itself in those rare cases. 990 $ok = $this->relayNonVolatilePurge( $valueSisterKey ); 991 } else { 992 // A cacheable entity recently changed, so there might be a volatility period due 993 // to replica DB lag. Clients usually expect their actions to be reflected in any 994 // of their subsequent web request. This is attainable if (a) purge relay lag is 995 // lower than the time it takes for subsequent request by the client to arrive, 996 // and, (b) DB replica queries have "read-your-writes" consistency due to DB lag 997 // mitigation systems. 998 999 $now = $this->getCurrentTime(); 1000 // Set the key to the purge value in all datacenters 1001 $purgeBySisterKey = [ $valueSisterKey => $this->makeTombstonePurgeValue( $now ) ]; 1002 // When an on-host tier is configured, invalidate it by setting "flux" keys 1003 if ( $this->onHostRoute !== null ) { 1004 $fluxSisterKey = $this->makeSisterKey( $key, self::TYPE_FLUX ); 1005 $purgeBySisterKey[$fluxSisterKey] = $this->makeTombstonePurgeValue( $now ); 1006 } 1007 1008 $ok = $this->relayVolatilePurges( $purgeBySisterKey, $ttl ); 1009 } 1010 1011 $kClass = $this->determineKeyClassForStats( $key ); 1012 $this->stats->increment( "wanobjectcache.$kClass.delete." . ( $ok ? 'ok' : 'error' ) ); 1013 1014 return $ok; 1015 } 1016 1017 /** 1018 * Fetch the value of a timestamp "check" key 1019 * 1020 * The key will be *initialized* to the current time if not set, 1021 * so only call this method if this behavior is actually desired 1022 * 1023 * The timestamp can be used to check whether a cached value is valid. 1024 * Callers should not assume that this returns the same timestamp in 1025 * all datacenters due to relay delays. 1026 * 1027 * The level of staleness can roughly be estimated from this key, but 1028 * if the key was evicted from cache, such calculations may show the 1029 * time since expiry as ~0 seconds. 1030 * 1031 * Note that "check" keys won't collide with other regular keys. 1032 * 1033 * @param string $key Cache key made with makeKey()/makeGlobalKey() 1034 * @return float UNIX timestamp 1035 */ 1036 final public function getCheckKeyTime( $key ) { 1037 return $this->getMultiCheckKeyTime( [ $key ] )[$key]; 1038 } 1039 1040 /** 1041 * Fetch the values of each timestamp "check" key 1042 * 1043 * This works like getCheckKeyTime() except it takes a list of keys 1044 * and returns a map of timestamps instead of just that of one key 1045 * 1046 * This might be useful if both: 1047 * - a) a class of entities each depend on hundreds of other entities 1048 * - b) these other entities are depended upon by millions of entities 1049 * 1050 * The later entities can each use a "check" key to invalidate their dependee entities. 1051 * However, it is expensive for the former entities to verify against all of the relevant 1052 * "check" keys during each getWithSetCallback() call. A less expensive approach is to do 1053 * these verifications only after a "time-till-verify" (TTV) has passed. This is a middle 1054 * ground between using blind TTLs and using constant verification. The adaptiveTTL() method 1055 * can be used to dynamically adjust the TTV. Also, the initial TTV can make use of the 1056 * last-modified times of the dependent entities (either from the DB or the "check" keys). 1057 * 1058 * Example usage: 1059 * @code 1060 * $value = $cache->getWithSetCallback( 1061 * $cache->makeGlobalKey( 'wikibase-item', $id ), 1062 * self::INITIAL_TTV, // initial time-till-verify 1063 * function ( $oldValue, &$ttv, &$setOpts, $oldAsOf ) use ( $checkKeys, $cache ) { 1064 * $now = microtime( true ); 1065 * // Use $oldValue if it passes max ultimate age and "check" key comparisons 1066 * if ( $oldValue && 1067 * $oldAsOf > max( $cache->getMultiCheckKeyTime( $checkKeys ) ) && 1068 * ( $now - $oldValue['ctime'] ) <= self::MAX_CACHE_AGE 1069 * ) { 1070 * // Increase time-till-verify by 50% of last time to reduce overhead 1071 * $ttv = $cache->adaptiveTTL( $oldAsOf, self::MAX_TTV, self::MIN_TTV, 1.5 ); 1072 * // Unlike $oldAsOf, "ctime" is the ultimate age of the cached data 1073 * return $oldValue; 1074 * } 1075 * 1076 * $mtimes = []; // dependency last-modified times; passed by reference 1077 * $value = [ 'data' => $this->fetchEntityData( $mtimes ), 'ctime' => $now ]; 1078 * // Guess time-till-change among the dependencies, e.g. 1/(total change rate) 1079 * $ttc = 1 / array_sum( array_map( 1080 * function ( $mtime ) use ( $now ) { 1081 * return 1 / ( $mtime ? ( $now - $mtime ) : 900 ); 1082 * }, 1083 * $mtimes 1084 * ) ); 1085 * // The time-to-verify should not be overly pessimistic nor optimistic 1086 * $ttv = min( max( $ttc, self::MIN_TTV ), self::MAX_TTV ); 1087 * 1088 * return $value; 1089 * }, 1090 * [ 'staleTTL' => $cache::TTL_DAY ] // keep around to verify and re-save 1091 * ); 1092 * @endcode 1093 * 1094 * @see WANObjectCache::getCheckKeyTime() 1095 * @see WANObjectCache::getWithSetCallback() 1096 * 1097 * @param string[] $keys Cache keys made with makeKey()/makeGlobalKey() 1098 * @return float[] Map of (key => UNIX timestamp) 1099 * @since 1.31 1100 */ 1101 final public function getMultiCheckKeyTime( array $keys ) { 1102 $checkSisterKeysByKey = []; 1103 foreach ( $keys as $key ) { 1104 $checkSisterKeysByKey[$key] = $this->makeSisterKey( $key, self::TYPE_TIMESTAMP ); 1105 } 1106 1107 $wrappedBySisterKey = $this->cache->getMulti( $checkSisterKeysByKey ); 1108 $wrappedBySisterKey += array_fill_keys( $checkSisterKeysByKey, false ); 1109 1110 $times = []; 1111 foreach ( $checkSisterKeysByKey as $key => $checkSisterKey ) { 1112 $purge = $this->parsePurgeValue( $wrappedBySisterKey[$checkSisterKey] ); 1113 if ( $purge !== false ) { 1114 $time = $purge[self::PURGE_TIME]; 1115 } else { 1116 // Casting assures identical floats for the next getCheckKeyTime() calls 1117 $now = (string)$this->getCurrentTime(); 1118 $this->cache->add( 1119 $checkSisterKey, 1120 $this->makeCheckPurgeValue( $now, self::HOLDOFF_TTL ), 1121 self::CHECK_KEY_TTL 1122 ); 1123 $time = (float)$now; 1124 } 1125 1126 $times[$key] = $time; 1127 } 1128 1129 return $times; 1130 } 1131 1132 /** 1133 * Purge a "check" key from all datacenters, invalidating keys that use it 1134 * 1135 * This should only be called when the underlying data (being cached) 1136 * changes in a significant way, and it is impractical to call delete() 1137 * on all keys that should be changed. When get() is called on those 1138 * keys, the relevant "check" keys must be supplied for this to work. 1139 * 1140 * The "check" key essentially represents a last-modified time of an entity. 1141 * When the key is touched, the timestamp will be updated to the current time. 1142 * Keys using the "check" key via get(), getMulti(), or getWithSetCallback() will 1143 * be invalidated. This approach is useful if many keys depend on a single entity. 1144 * 1145 * The timestamp of the "check" key is treated as being HOLDOFF_TTL seconds in the 1146 * future by get*() methods in order to avoid race conditions where keys are updated 1147 * with stale values (e.g. from a lagged replica DB). A high TTL is set on the "check" 1148 * key, making it possible to know the timestamp of the last change to the corresponding 1149 * entities in most cases. This might use more cache space than resetCheckKey(). 1150 * 1151 * When a few important keys get a large number of hits, a high cache time is usually 1152 * desired as well as "lockTSE" logic. The resetCheckKey() method is less appropriate 1153 * in such cases since the "time since expiry" cannot be inferred, causing any get() 1154 * after the reset to treat the key as being "hot", resulting in more stale value usage. 1155 * 1156 * Note that "check" keys won't collide with other regular keys. 1157 * 1158 * @see WANObjectCache::get() 1159 * @see WANObjectCache::getWithSetCallback() 1160 * @see WANObjectCache::resetCheckKey() 1161 * 1162 * @param string $key Cache key made with makeKey()/makeGlobalKey() 1163 * @param int $holdoff HOLDOFF_TTL or HOLDOFF_TTL_NONE constant 1164 * @return bool True if the item was purged or not found, false on failure 1165 */ 1166 final public function touchCheckKey( $key, $holdoff = self::HOLDOFF_TTL ) { 1167 $checkSisterKey = $this->makeSisterKey( $key, self::TYPE_TIMESTAMP ); 1168 $ok = $this->relayVolatilePurges( 1169 [ $checkSisterKey => $this->makeCheckPurgeValue( $this->getCurrentTime(), $holdoff ) ], 1170 self::CHECK_KEY_TTL 1171 ); 1172 1173 $kClass = $this->determineKeyClassForStats( $key ); 1174 $this->stats->increment( "wanobjectcache.$kClass.ck_touch." . ( $ok ? 'ok' : 'error' ) ); 1175 1176 return $ok; 1177 } 1178 1179 /** 1180 * Delete a "check" key from all datacenters, invalidating keys that use it 1181 * 1182 * This is similar to touchCheckKey() in that keys using it via get(), getMulti(), 1183 * or getWithSetCallback() will be invalidated. The differences are: 1184 * - a) The "check" key will be deleted from all caches and lazily 1185 * re-initialized when accessed (rather than set everywhere) 1186 * - b) Thus, dependent keys will be known to be stale, but not 1187 * for how long (they are treated as "just" purged), which 1188 * effects any lockTSE logic in getWithSetCallback() 1189 * - c) Since "check" keys are initialized only on the server the key hashes 1190 * to, any temporary ejection of that server will cause the value to be 1191 * seen as purged as a new server will initialize the "check" key. 1192 * 1193 * The advantage here is that the "check" keys, which have high TTLs, will only 1194 * be created when a get*() method actually uses that key. This is better when 1195 * a large number of "check" keys are invalided in a short period of time. 1196 * 1197 * Note that "check" keys won't collide with other regular keys. 1198 * 1199 * @see WANObjectCache::get() 1200 * @see WANObjectCache::getWithSetCallback() 1201 * @see WANObjectCache::touchCheckKey() 1202 * 1203 * @param string $key Cache key made with makeKey()/makeGlobalKey() 1204 * @return bool True if the item was purged or not found, false on failure 1205 */ 1206 final public function resetCheckKey( $key ) { 1207 $checkSisterKey = $this->makeSisterKey( $key, self::TYPE_TIMESTAMP ); 1208 $ok = $this->relayNonVolatilePurge( $checkSisterKey ); 1209 1210 $kClass = $this->determineKeyClassForStats( $key ); 1211 $this->stats->increment( "wanobjectcache.$kClass.ck_reset." . ( $ok ? 'ok' : 'error' ) ); 1212 1213 return $ok; 1214 } 1215 1216 /** 1217 * Method to fetch/regenerate a cache key 1218 * 1219 * On cache miss, the key will be set to the callback result via set() 1220 * (unless the callback returns false) and that result will be returned. 1221 * The arguments supplied to the callback are: 1222 * - $oldValue: prior cache value or false if none was present 1223 * - &$ttl: alterable reference to the TTL to be assigned to the new value 1224 * - &$setOpts: alterable reference to the set() options to be used with the new value 1225 * - $oldAsOf: generation UNIX timestamp of $oldValue or null if not present (since 1.28) 1226 * - $params: custom field/value map as defined by $cbParams (since 1.35) 1227 * 1228 * It is strongly recommended to set the 'lag' and 'since' fields to avoid race conditions 1229 * that can cause stale values to get stuck at keys. Usually, callbacks ignore the current 1230 * value, but it can be used to maintain "most recent X" values that come from time or 1231 * sequence based source data, provided that the "as of" id/time is tracked. Note that 1232 * preemptive regeneration and $checkKeys can result in a non-false current value. 1233 * 1234 * Usage of $checkKeys is similar to get() and getMulti(). However, rather than the caller 1235 * having to inspect a "current time left" variable (e.g. $curTTL, $curTTLs), a cache 1236 * regeneration will automatically be triggered using the callback. 1237 * 1238 * The $ttl argument and "hotTTR" option (in $opts) use time-dependent randomization 1239 * to avoid stampedes. Keys that are slow to regenerate and either heavily used 1240 * or subject to explicit (unpredictable) purges, may need additional mechanisms. 1241 * The simplest way to avoid stampedes for such keys is to use 'lockTSE' (in $opts). 1242 * If explicit purges are needed, also: 1243 * - a) Pass $key into $checkKeys 1244 * - b) Use touchCheckKey( $key ) instead of delete( $key ) 1245 * 1246 * This applies cache server I/O stampede protection against duplicate cache sets. 1247 * This is important when the callback is slow and/or yields large values for a key. 1248 * 1249 * Example usage (typical key): 1250 * @code 1251 * $catInfo = $cache->getWithSetCallback( 1252 * // Key to store the cached value under 1253 * $cache->makeKey( 'cat-attributes', $catId ), 1254 * // Time-to-live (in seconds) 1255 * $cache::TTL_MINUTE, 1256 * // Function that derives the new key value 1257 * function ( $oldValue, &$ttl, array &$setOpts ) { 1258 * $dbr = wfGetDB( DB_REPLICA ); 1259 * // Account for any snapshot/replica DB lag 1260 * $setOpts += Database::getCacheSetOptions( $dbr ); 1261 * 1262 * return $dbr->selectRow( ... ); 1263 * } 1264 * ); 1265 * @endcode 1266 * 1267 * Example usage (key that is expensive and hot): 1268 * @code 1269 * $catConfig = $cache->getWithSetCallback( 1270 * // Key to store the cached value under 1271 * $cache->makeKey( 'site-cat-config' ), 1272 * // Time-to-live (in seconds) 1273 * $cache::TTL_DAY, 1274 * // Function that derives the new key value 1275 * function ( $oldValue, &$ttl, array &$setOpts ) { 1276 * $dbr = wfGetDB( DB_REPLICA ); 1277 * // Account for any snapshot/replica DB lag 1278 * $setOpts += Database::getCacheSetOptions( $dbr ); 1279 * 1280 * return CatConfig::newFromRow( $dbr->selectRow( ... ) ); 1281 * }, 1282 * [ 1283 * // Calling touchCheckKey() on this key invalidates the cache 1284 * 'checkKeys' => [ $cache->makeKey( 'site-cat-config' ) ], 1285 * // Try to only let one datacenter thread manage cache updates at a time 1286 * 'lockTSE' => 30, 1287 * // Avoid querying cache servers multiple times in a web request 1288 * 'pcTTL' => $cache::TTL_PROC_LONG 1289 * ] 1290 * ); 1291 * @endcode 1292 * 1293 * Example usage (key with dynamic dependencies): 1294 * @code 1295 * $catState = $cache->getWithSetCallback( 1296 * // Key to store the cached value under 1297 * $cache->makeKey( 'cat-state', $cat->getId() ), 1298 * // Time-to-live (seconds) 1299 * $cache::TTL_HOUR, 1300 * // Function that derives the new key value 1301 * function ( $oldValue, &$ttl, array &$setOpts ) { 1302 * // Determine new value from the DB 1303 * $dbr = wfGetDB( DB_REPLICA ); 1304 * // Account for any snapshot/replica DB lag 1305 * $setOpts += Database::getCacheSetOptions( $dbr ); 1306 * 1307 * return CatState::newFromResults( $dbr->select( ... ) ); 1308 * }, 1309 * [ 1310 * // The "check" keys that represent things the value depends on; 1311 * // Calling touchCheckKey() on any of them invalidates the cache 1312 * 'checkKeys' => [ 1313 * $cache->makeKey( 'sustenance-bowls', $cat->getRoomId() ), 1314 * $cache->makeKey( 'people-present', $cat->getHouseId() ), 1315 * $cache->makeKey( 'cat-laws', $cat->getCityId() ), 1316 * ] 1317 * ] 1318 * ); 1319 * @endcode 1320 * 1321 * Example usage (key that is expensive with too many DB dependencies for "check" keys): 1322 * @code 1323 * $catToys = $cache->getWithSetCallback( 1324 * // Key to store the cached value under 1325 * $cache->makeKey( 'cat-toys', $catId ), 1326 * // Time-to-live (seconds) 1327 * $cache::TTL_HOUR, 1328 * // Function that derives the new key value 1329 * function ( $oldValue, &$ttl, array &$setOpts ) { 1330 * // Determine new value from the DB 1331 * $dbr = wfGetDB( DB_REPLICA ); 1332 * // Account for any snapshot/replica DB lag 1333 * $setOpts += Database::getCacheSetOptions( $dbr ); 1334 * 1335 * return CatToys::newFromResults( $dbr->select( ... ) ); 1336 * }, 1337 * [ 1338 * // Get the highest timestamp of any of the cat's toys 1339 * 'touchedCallback' => function ( $value ) use ( $catId ) { 1340 * $dbr = wfGetDB( DB_REPLICA ); 1341 * $ts = $dbr->selectField( 'cat_toys', 'MAX(ct_touched)', ... ); 1342 * 1343 * return wfTimestampOrNull( TS_UNIX, $ts ); 1344 * }, 1345 * // Avoid DB queries for repeated access 1346 * 'pcTTL' => $cache::TTL_PROC_SHORT 1347 * ] 1348 * ); 1349 * @endcode 1350 * 1351 * Example usage (hot key holding most recent 100 events): 1352 * @code 1353 * $lastCatActions = $cache->getWithSetCallback( 1354 * // Key to store the cached value under 1355 * $cache->makeKey( 'cat-last-actions', 100 ), 1356 * // Time-to-live (in seconds) 1357 * 10, 1358 * // Function that derives the new key value 1359 * function ( $oldValue, &$ttl, array &$setOpts ) { 1360 * $dbr = wfGetDB( DB_REPLICA ); 1361 * // Account for any snapshot/replica DB lag 1362 * $setOpts += Database::getCacheSetOptions( $dbr ); 1363 * 1364 * // Start off with the last cached list 1365 * $list = $oldValue ?: []; 1366 * // Fetch the last 100 relevant rows in descending order; 1367 * // only fetch rows newer than $list[0] to reduce scanning 1368 * $rows = iterator_to_array( $dbr->select( ... ) ); 1369 * // Merge them and get the new "last 100" rows 1370 * return array_slice( array_merge( $new, $list ), 0, 100 ); 1371 * }, 1372 * [ 1373 * // Try to only let one datacenter thread manage cache updates at a time 1374 * 'lockTSE' => 30, 1375 * // Use a magic value when no cache value is ready rather than stampeding 1376 * 'busyValue' => 'computing' 1377 * ] 1378 * ); 1379 * @endcode 1380 * 1381 * Example usage (key holding an LRU subkey:value map; this can avoid flooding cache with 1382 * keys for an unlimited set of (constraint,situation) pairs, thereby avoiding elevated 1383 * cache evictions and wasted memory): 1384 * @code 1385 * $catSituationTolerabilityCache = $this->cache->getWithSetCallback( 1386 * // Group by constraint ID/hash, cat family ID/hash, or something else useful 1387 * $this->cache->makeKey( 'cat-situation-tolerability-checks', $groupKey ), 1388 * WANObjectCache::TTL_DAY, // rarely used groups should fade away 1389 * // The $scenarioKey format is $constraintId:<ID/hash of $situation> 1390 * function ( $cacheMap ) use ( $scenarioKey, $constraintId, $situation ) { 1391 * $lruCache = MapCacheLRU::newFromArray( $cacheMap ?: [], self::CACHE_SIZE ); 1392 * $result = $lruCache->get( $scenarioKey ); // triggers LRU bump if present 1393 * if ( $result === null || $this->isScenarioResultExpired( $result ) ) { 1394 * $result = $this->checkScenarioTolerability( $constraintId, $situation ); 1395 * $lruCache->set( $scenarioKey, $result, 3 / 8 ); 1396 * } 1397 * // Save the new LRU cache map and reset the map's TTL 1398 * return $lruCache->toArray(); 1399 * }, 1400 * [ 1401 * // Once map is > 1 sec old, consider refreshing 1402 * 'ageNew' => 1, 1403 * // Update within 5 seconds after "ageNew" given a 1hz cache check rate 1404 * 'hotTTR' => 5, 1405 * // Avoid querying cache servers multiple times in a request; this also means 1406 * // that a request can only alter the value of any given constraint key once 1407 * 'pcTTL' => WANObjectCache::TTL_PROC_LONG 1408 * ] 1409 * ); 1410 * $tolerability = isset( $catSituationTolerabilityCache[$scenarioKey] ) 1411 * ? $catSituationTolerabilityCache[$scenarioKey] 1412 * : $this->checkScenarioTolerability( $constraintId, $situation ); 1413 * @endcode 1414 * 1415 * @see WANObjectCache::get() 1416 * @see WANObjectCache::set() 1417 * 1418 * @param string $key Cache key made with makeKey()/makeGlobalKey() 1419 * @param int $ttl Nominal seconds-to-live for newly computed values. Special values are: 1420 * - WANObjectCache::TTL_INDEFINITE: Cache forever (subject to LRU-style evictions) 1421 * - WANObjectCache::TTL_UNCACHEABLE: Do not cache (if the key exists, it is not deleted) 1422 * @param callable $callback Value generation function 1423 * @param array $opts Options map: 1424 * - checkKeys: List of "check" keys. The key at $key will be seen as stale when either 1425 * touchCheckKey() or resetCheckKey() is called on any of the keys in this list. This 1426 * is useful if thousands or millions of keys depend on the same entity. The entity can 1427 * simply have its "check" key updated whenever the entity is modified. 1428 * Default: []. 1429 * - graceTTL: If the key is invalidated (by "checkKeys" or "touchedCallback") less than 1430 * this many seconds ago, consider reusing the stale value. The odds of a refresh become 1431 * more likely over time, becoming certain once the grace period is reached. This can 1432 * reduce traffic spikes when millions of keys are compared to the same "check" key and 1433 * touchCheckKey() or resetCheckKey() is called on that "check" key. This option is not 1434 * useful for avoiding traffic spikes in the case of the key simply expiring on account 1435 * of its TTL (use "lowTTL" instead). 1436 * Default: WANObjectCache::GRACE_TTL_NONE. 1437 * - lockTSE: Prefer the use of a mutex during value regeneration of the key if its TSE 1438 * ("time since expiry") is less than the given number of seconds ago. The TSE is 1439 * influenced by deletion, invalidation (e.g. by "checkKeys" or "touchedCallback"), 1440 * and various other options (e.g. "staleTTL"). A low enough TSE is assumed to indicate 1441 * a high enough key access rate to justify stampede avoidance. A thread that tries and 1442 * fails to acquire the mutex will use a stale value for the key, if there is one, and, 1443 * if not, it will execute the callback. Note that no cache value exists after deletion 1444 * or storage-layer expiration/eviction; to prevent stampedes during these cases, avoid 1445 * using delete(), keep "lowTTL" enabled, and consider using "busyValue". 1446 * Default: WANObjectCache::TSE_NONE. 1447 * - busyValue: Specify a placeholder value to use when no value exists and another thread 1448 * is currently regenerating it. This assures that cache stampedes cannot happen if the 1449 * value falls out of cache. This also mitigates stampedes when value regeneration 1450 * becomes very slow (greater than $ttl/"lowTTL"). If this is a closure, then it will 1451 * be invoked to get the placeholder when needed. 1452 * Default: null. 1453 * - pcTTL: Process cache the value in this PHP instance for this many seconds. This avoids 1454 * network I/O when a key is read several times. This will not cache when the callback 1455 * returns false, however. Note that any purges will not be seen while process cached; 1456 * since the callback should use replica DBs and they may be lagged or have snapshot 1457 * isolation anyway, this should not typically matter. 1458 * Default: WANObjectCache::TTL_UNCACHEABLE. 1459 * - pcGroup: Process cache group to use instead of the primary one. If set, this must be 1460 * of the format ALPHANUMERIC_NAME:MAX_KEY_SIZE, e.g. "mydata:10". Use this for storing 1461 * large values, small yet numerous values, or some values with a high cost of eviction. 1462 * It is generally preferable to use a class constant when setting this value. 1463 * This has no effect unless pcTTL is used. 1464 * Default: WANObjectCache::PC_PRIMARY. 1465 * - version: Integer version number. This lets callers make breaking changes to the format 1466 * of cached values without causing problems for sites that use non-instantaneous code 1467 * deployments. Old and new code will recognize incompatible versions and purges from 1468 * both old and new code will been seen by each other. When this method encounters an 1469 * incompatibly versioned value at the provided key, a "variant key" will be used for 1470 * reading from and saving to cache. The variant key is specific to the key and version 1471 * number provided to this method. If the variant key value is older than that of the 1472 * provided key, or the provided key is non-existant, then the variant key will be seen 1473 * as non-existant. Therefore, delete() calls invalidate the provided key's variant keys. 1474 * The "checkKeys" and "touchedCallback" options still apply to variant keys as usual. 1475 * Avoid storing class objects, as this reduces compatibility (due to serialization). 1476 * Default: null. 1477 * - minAsOf: Reject values if they were generated before this UNIX timestamp. 1478 * This is useful if the source of a key is suspected of having possibly changed 1479 * recently, and the caller wants any such changes to be reflected. 1480 * Default: WANObjectCache::MIN_TIMESTAMP_NONE. 1481 * - hotTTR: Expected time-till-refresh (TTR) in seconds for keys that average ~1 hit per 1482 * second (e.g. 1Hz). Keys with a hit rate higher than 1Hz will refresh sooner than this 1483 * TTR and vise versa. Such refreshes won't happen until keys are "ageNew" seconds old. 1484 * This uses randomization to avoid triggering cache stampedes. The TTR is useful at 1485 * reducing the impact of missed cache purges, since the effect of a heavily referenced 1486 * key being stale is worse than that of a rarely referenced key. Unlike simply lowering 1487 * $ttl, seldomly used keys are largely unaffected by this option, which makes it 1488 * possible to have a high hit rate for the "long-tail" of less-used keys. 1489 * Default: WANObjectCache::HOT_TTR. 1490 * - lowTTL: Consider pre-emptive updates when the current TTL (seconds) of the key is less 1491 * than this. It becomes more likely over time, becoming certain once the key is expired. 1492 * This helps avoid cache stampedes that might be triggered due to the key expiring. 1493 * Default: WANObjectCache::LOW_TTL. 1494 * - ageNew: Consider popularity refreshes only once a key reaches this age in seconds. 1495 * Default: WANObjectCache::AGE_NEW. 1496 * - staleTTL: Seconds to keep the key around if it is stale. This means that on cache 1497 * miss the callback may get $oldValue/$oldAsOf values for keys that have already been 1498 * expired for this specified time. This is useful if adaptiveTTL() is used on the old 1499 * value's as-of time when it is verified as still being correct. 1500 * Default: WANObjectCache::STALE_TTL_NONE 1501 * - touchedCallback: A callback that takes the current value and returns a UNIX timestamp 1502 * indicating the last time a dynamic dependency changed. Null can be returned if there 1503 * are no relevant dependency changes to check. This can be used to check against things 1504 * like last-modified times of files or DB timestamp fields. This should generally not be 1505 * used for small and easily queried values in a DB if the callback itself ends up doing 1506 * a similarly expensive DB query to check a timestamp. Usages of this option makes the 1507 * most sense for values that are moderately to highly expensive to regenerate and easy 1508 * to query for dependency timestamps. The use of "pcTTL" reduces timestamp queries. 1509 * Default: null. 1510 * @param array $cbParams Custom field/value map to pass to the callback (since 1.35) 1511 * @phpcs:ignore Generic.Files.LineLength 1512 * @phan-param array{checkKeys?:string[],graceTTL?:int,lockTSE?:int,busyValue?:mixed,pcTTL?:int,pcGroup?:string,version?:int,minAsOf?:float|int,hotTTR?:int,lowTTL?:int,ageNew?:int,staleTTL?:int,touchedCallback?:callable} $opts 1513 * @return mixed Value found or written to the key 1514 * @note Options added in 1.28: version, busyValue, hotTTR, ageNew, pcGroup, minAsOf 1515 * @note Options added in 1.31: staleTTL, graceTTL 1516 * @note Options added in 1.33: touchedCallback 1517 * @note Callable type hints are not used to avoid class-autoloading 1518 */ 1519 final public function getWithSetCallback( 1520 $key, $ttl, $callback, array $opts = [], array $cbParams = [] 1521 ) { 1522 $version = $opts['version'] ?? null; 1523 $pcTTL = $opts['pcTTL'] ?? self::TTL_UNCACHEABLE; 1524 $pCache = ( $pcTTL >= 0 ) 1525 ? $this->getProcessCache( $opts['pcGroup'] ?? self::PC_PRIMARY ) 1526 : null; 1527 1528 // Use the process cache if requested as long as no outer cache callback is running. 1529 // Nested callback process cache use is not lag-safe with regard to HOLDOFF_TTL since 1530 // process cached values are more lagged than persistent ones as they are not purged. 1531 if ( $pCache && $this->callbackDepth == 0 ) { 1532 $cached = $pCache->get( $this->getProcessCacheKey( $key, $version ), $pcTTL, false ); 1533 if ( $cached !== false ) { 1534 $this->logger->debug( "getWithSetCallback($key): process cache hit" ); 1535 return $cached; 1536 } 1537 } 1538 1539 $res = $this->fetchOrRegenerate( $key, $ttl, $callback, $opts, $cbParams ); 1540 list( $value, $valueVersion, $curAsOf ) = $res; 1541 if ( $valueVersion !== $version ) { 1542 // Current value has a different version; use the variant key for this version. 1543 // Regenerate the variant value if it is not newer than the main value at $key 1544 // so that purges to the main key propagate to the variant value. 1545 $this->logger->debug( "getWithSetCallback($key): using variant key" ); 1546 list( $value ) = $this->fetchOrRegenerate( 1547 $this->makeGlobalKey( 'WANCache-key-variant', md5( $key ), $version ), 1548 $ttl, 1549 $callback, 1550 [ 'version' => null, 'minAsOf' => $curAsOf ] + $opts, 1551 $cbParams 1552 ); 1553 } 1554 1555 // Update the process cache if enabled 1556 if ( $pCache && $value !== false ) { 1557 $pCache->set( $this->getProcessCacheKey( $key, $version ), $value ); 1558 } 1559 1560 return $value; 1561 } 1562 1563 /** 1564 * Do the actual I/O for getWithSetCallback() when needed 1565 * 1566 * @see WANObjectCache::getWithSetCallback() 1567 * 1568 * @param string $key Cache key made with makeKey()/makeGlobalKey() 1569 * @param int $ttl 1570 * @param callable $callback 1571 * @param array $opts 1572 * @param array $cbParams 1573 * @return array Ordered list of the following: 1574 * - Cached or regenerated value 1575 * - Cached or regenerated value version number or null if not versioned 1576 * - Timestamp of the current cached value at the key or null if there is no value 1577 * @note Callable type hints are not used to avoid class-autoloading 1578 */ 1579 private function fetchOrRegenerate( $key, $ttl, $callback, array $opts, array $cbParams ) { 1580 $checkKeys = $opts['checkKeys'] ?? []; 1581 $graceTTL = $opts['graceTTL'] ?? self::GRACE_TTL_NONE; 1582 $minAsOf = $opts['minAsOf'] ?? self::MIN_TIMESTAMP_NONE; 1583 $hotTTR = $opts['hotTTR'] ?? self::HOT_TTR; 1584 $lowTTL = $opts['lowTTL'] ?? min( self::LOW_TTL, $ttl ); 1585 $ageNew = $opts['ageNew'] ?? self::AGE_NEW; 1586 $touchedCb = $opts['touchedCallback'] ?? null; 1587 $initialTime = $this->getCurrentTime(); 1588 1589 $kClass = $this->determineKeyClassForStats( $key ); 1590 1591 // Get the current key value and its metadata 1592 $res = $this->fetchKeys( [ $key ], $checkKeys )[$key]; 1593 $curValue = $res[self::RES_VALUE]; 1594 $curInfo = $res[self::RES_METADATA]; 1595 $curTTL = $curInfo[self::KEY_CUR_TTL]; 1596 // Apply any $touchedCb invalidation timestamp to get the "last purge timestamp" 1597 list( $curTTL, $LPT ) = $this->resolveCTL( $curValue, $curTTL, $curInfo, $touchedCb ); 1598 // Use the cached value if it exists and is not due for synchronous regeneration 1599 if ( 1600 $this->isValid( $curValue, $curInfo[self::KEY_AS_OF], $minAsOf ) && 1601 $this->isAliveOrInGracePeriod( $curTTL, $graceTTL ) 1602 ) { 1603 $preemptiveRefresh = ( 1604 $this->worthRefreshExpiring( $curTTL, $curInfo[self::KEY_TTL], $lowTTL ) || 1605 $this->worthRefreshPopular( $curInfo['asOf'], $ageNew, $hotTTR, $initialTime ) 1606 ); 1607 if ( !$preemptiveRefresh ) { 1608 $this->stats->timing( 1609 "wanobjectcache.$kClass.hit.good", 1610 1e3 * ( $this->getCurrentTime() - $initialTime ) 1611 ); 1612 1613 return [ $curValue, $curInfo[self::KEY_VERSION], $curInfo[self::KEY_AS_OF] ]; 1614 } elseif ( $this->scheduleAsyncRefresh( $key, $ttl, $callback, $opts, $cbParams ) ) { 1615 $this->logger->debug( "fetchOrRegenerate($key): hit with async refresh" ); 1616 $this->stats->timing( 1617 "wanobjectcache.$kClass.hit.refresh", 1618 1e3 * ( $this->getCurrentTime() - $initialTime ) 1619 ); 1620 1621 return [ $curValue, $curInfo[self::KEY_VERSION], $curInfo[self::KEY_AS_OF] ]; 1622 } else { 1623 $this->logger->debug( "fetchOrRegenerate($key): hit with sync refresh" ); 1624 } 1625 } 1626 1627 // Determine if there is stale or volatile cached value that is still usable 1628 $isKeyTombstoned = ( $curInfo[self::KEY_TOMB_AS_OF] !== null ); 1629 if ( $isKeyTombstoned ) { 1630 // Key is write-holed; use the (volatile) interim key as an alternative 1631 list( $possValue, $possInfo ) = $this->getInterimValue( $key, $minAsOf ); 1632 // Update the "last purge time" since the $touchedCb timestamp depends on $value 1633 $LPT = $this->resolveTouched( $possValue, $LPT, $touchedCb ); 1634 } else { 1635 $possValue = $curValue; 1636 $possInfo = $curInfo; 1637 } 1638 1639 // Avoid overhead from callback runs, regeneration locks, and cache sets during 1640 // hold-off periods for the key by reusing very recently generated cached values 1641 if ( 1642 $this->isValid( $possValue, $possInfo[self::KEY_AS_OF], $minAsOf, $LPT ) && 1643 $this->isVolatileValueAgeNegligible( $initialTime - $possInfo[self::KEY_AS_OF] ) 1644 ) { 1645 $this->logger->debug( "fetchOrRegenerate($key): volatile hit" ); 1646 $this->stats->timing( 1647 "wanobjectcache.$kClass.hit.volatile", 1648 1e3 * ( $this->getCurrentTime() - $initialTime ) 1649 ); 1650 1651 return [ $possValue, $possInfo[self::KEY_VERSION], $curInfo[self::KEY_AS_OF] ]; 1652 } 1653 1654 $lockTSE = $opts['lockTSE'] ?? self::TSE_NONE; 1655 $busyValue = $opts['busyValue'] ?? null; 1656 $staleTTL = $opts['staleTTL'] ?? self::STALE_TTL_NONE; 1657 $version = $opts['version'] ?? null; 1658 1659 // Determine whether one thread per datacenter should handle regeneration at a time 1660 $useRegenerationLock = 1661 // Note that since tombstones no-op set(), $lockTSE and $curTTL cannot be used to 1662 // deduce the key hotness because |$curTTL| will always keep increasing until the 1663 // tombstone expires or is overwritten by a new tombstone. Also, even if $lockTSE 1664 // is not set, constant regeneration of a key for the tombstone lifetime might be 1665 // very expensive. Assume tombstoned keys are possibly hot in order to reduce 1666 // the risk of high regeneration load after the delete() method is called. 1667 $isKeyTombstoned || 1668 // Assume a key is hot if requested soon ($lockTSE seconds) after invalidation. 1669 // This avoids stampedes when timestamps from $checkKeys/$touchedCb bump. 1670 ( $curTTL !== null && $curTTL <= 0 && abs( $curTTL ) <= $lockTSE ) || 1671 // Assume a key is hot if there is no value and a busy fallback is given. 1672 // This avoids stampedes on eviction or preemptive regeneration taking too long. 1673 ( $busyValue !== null && $possValue === false ); 1674 1675 // If a regeneration lock is required, threads that do not get the lock will try to use 1676 // the stale value, the interim value, or the $busyValue placeholder, in that order. If 1677 // none of those are set then all threads will bypass the lock and regenerate the value. 1678 $hasLock = $useRegenerationLock && $this->claimStampedeLock( $key ); 1679 if ( $useRegenerationLock && !$hasLock ) { 1680 if ( $this->isValid( $possValue, $possInfo[self::KEY_AS_OF], $minAsOf ) ) { 1681 $this->logger->debug( "fetchOrRegenerate($key): returning stale value" ); 1682 $this->stats->timing( 1683 "wanobjectcache.$kClass.hit.stale", 1684 1e3 * ( $this->getCurrentTime() - $initialTime ) 1685 ); 1686 1687 return [ $possValue, $possInfo[self::KEY_VERSION], $curInfo[self::KEY_AS_OF] ]; 1688 } elseif ( $busyValue !== null ) { 1689 $miss = is_infinite( $minAsOf ) ? 'renew' : 'miss'; 1690 $this->logger->debug( "fetchOrRegenerate($key): busy $miss" ); 1691 $this->stats->timing( 1692 "wanobjectcache.$kClass.$miss.busy", 1693 1e3 * ( $this->getCurrentTime() - $initialTime ) 1694 ); 1695 $placeholderValue = $this->resolveBusyValue( $busyValue ); 1696 1697 return [ $placeholderValue, $version, $curInfo[self::KEY_AS_OF] ]; 1698 } 1699 } 1700 1701 // Generate the new value given any prior value with a matching version 1702 $setOpts = []; 1703 $preCallbackTime = $this->getCurrentTime(); 1704 ++$this->callbackDepth; 1705 try { 1706 $value = $callback( 1707 ( $curInfo[self::KEY_VERSION] === $version ) ? $curValue : false, 1708 $ttl, 1709 $setOpts, 1710 ( $curInfo[self::KEY_VERSION] === $version ) ? $curInfo[self::KEY_AS_OF] : null, 1711 $cbParams 1712 ); 1713 } finally { 1714 --$this->callbackDepth; 1715 } 1716 $postCallbackTime = $this->getCurrentTime(); 1717 1718 // How long it took to fetch, validate, and generate the value 1719 $elapsed = max( $postCallbackTime - $initialTime, 0.0 ); 1720 1721 // Attempt to save the newly generated value if applicable 1722 if ( 1723 // Callback yielded a cacheable value 1724 ( $value !== false && $ttl >= 0 ) && 1725 // Current thread was not raced out of a regeneration lock or key is tombstoned 1726 ( !$useRegenerationLock || $hasLock || $isKeyTombstoned ) && 1727 // Key does not appear to be undergoing a set() stampede 1728 $this->checkAndSetCooloff( $key, $kClass, $value, $elapsed, $hasLock ) 1729 ) { 1730 // How long it took to generate the value 1731 $walltime = max( $postCallbackTime - $preCallbackTime, 0.0 ); 1732 $this->stats->timing( "wanobjectcache.$kClass.regen_walltime", 1e3 * $walltime ); 1733 // If the key is write-holed then use the (volatile) interim key as an alternative 1734 if ( $isKeyTombstoned ) { 1735 $this->setInterimValue( $key, $value, $lockTSE, $version, $walltime ); 1736 } else { 1737 $finalSetOpts = [ 1738 // @phan-suppress-next-line PhanUselessBinaryAddRight 1739 'since' => $setOpts['since'] ?? $preCallbackTime, 1740 'version' => $version, 1741 'staleTTL' => $staleTTL, 1742 'lockTSE' => $lockTSE, // informs lag vs performance trade-offs 1743 'creating' => ( $curValue === false ), // optimization 1744 'walltime' => $walltime 1745 ] + $setOpts; 1746 $this->set( $key, $value, $ttl, $finalSetOpts ); 1747 } 1748 } 1749 1750 $this->yieldStampedeLock( $key, $hasLock ); 1751 1752 $miss = is_infinite( $minAsOf ) ? 'renew' : 'miss'; 1753 $this->logger->debug( "fetchOrRegenerate($key): $miss, new value computed" ); 1754 $this->stats->timing( 1755 "wanobjectcache.$kClass.$miss.compute", 1756 1e3 * ( $this->getCurrentTime() - $initialTime ) 1757 ); 1758 1759 return [ $value, $version, $curInfo[self::KEY_AS_OF] ]; 1760 } 1761 1762 /** 1763 * @param string $key Cache key made with makeKey()/makeGlobalKey() 1764 * @return bool Success 1765 */ 1766 private function claimStampedeLock( $key ) { 1767 $checkSisterKey = $this->makeSisterKey( $key, self::TYPE_MUTEX ); 1768 // Note that locking is not bypassed due to I/O errors; this avoids stampedes 1769 return $this->cache->add( $checkSisterKey, 1, self::LOCK_TTL ); 1770 } 1771 1772 /** 1773 * @param string $key Cache key made with makeKey()/makeGlobalKey() 1774 * @param bool $hasLock 1775 */ 1776 private function yieldStampedeLock( $key, $hasLock ) { 1777 if ( $hasLock ) { 1778 $checkSisterKey = $this->makeSisterKey( $key, self::TYPE_MUTEX ); 1779 // The backend might be a mcrouter proxy set to broadcast DELETE to *all* the local 1780 // datacenter cache servers via OperationSelectorRoute (for increased consistency). 1781 // Since that would be excessive for these locks, use TOUCH to expire the key. 1782 $this->cache->changeTTL( $checkSisterKey, $this->getCurrentTime() - 60 ); 1783 } 1784 } 1785 1786 /** 1787 * Get sister keys that should be collocated with their corresponding base cache keys 1788 * 1789 * The key will bear the WANCache prefix and use the configured coalescing scheme 1790 * 1791 * @param string[] $baseKeys Cache keys made with makeKey()/makeGlobalKey() 1792 * @param string $type Consistent hashing agnostic suffix character matching [a-zA-Z] 1793 * @param string|null $route Routing prefix (optional) 1794 * @return string[] Order-corresponding list of sister keys 1795 */ 1796 private function makeSisterKeys( array $baseKeys, string $type, string $route = null ) { 1797 $sisterKeys = []; 1798 foreach ( $baseKeys as $baseKey ) { 1799 $sisterKeys[] = $this->makeSisterKey( $baseKey, $type, $route ); 1800 } 1801 1802 return $sisterKeys; 1803 } 1804 1805 /** 1806 * Get a sister key that should be collocated with a base cache key 1807 * 1808 * The keys will bear the WANCache prefix and use the configured coalescing scheme 1809 * 1810 * @param string $baseKey Cache key made with makeKey()/makeGlobalKey() 1811 * @param string $typeChar Consistent hashing agnostic suffix character matching [a-zA-Z] 1812 * @param string|null $route Routing prefix (optional) 1813 * @return string Sister key 1814 */ 1815 private function makeSisterKey( string $baseKey, string $typeChar, string $route = null ) { 1816 if ( $this->coalesceScheme === self::SCHEME_HASH_STOP ) { 1817 // Key style: "WANCache:<base key>|#|<character>" 1818 $sisterKey = 'WANCache:' . $baseKey . '|#|' . $typeChar; 1819 } else { 1820 // Key style: "WANCache:{<base key>}:<character>" 1821 $sisterKey = 'WANCache:{' . $baseKey . '}:' . $typeChar; 1822 } 1823 1824 if ( $route !== null ) { 1825 $sisterKey = $this->prependRoute( $sisterKey, $route ); 1826 } 1827 1828 return $sisterKey; 1829 } 1830 1831 /** 1832 * @param string $sisterKey Sister key from makeSisterKey() 1833 * @return string Key collection name 1834 * @internal For use by WANObjectCache/BagOStuff only 1835 * @since 1.36 1836 */ 1837 public static function getCollectionFromSisterKey( string $sisterKey ) { 1838 if ( substr( $sisterKey, -4 ) === '|#|v' ) { 1839 // Key style: "WANCache:<base key>|#|<character>" 1840 $collection = substr( $sisterKey, 9, strcspn( $sisterKey, ':|', 9 ) ); 1841 } elseif ( substr( $sisterKey, -3 ) === '}:v' ) { 1842 // Key style: "WANCache:{<base key>}:<character>" 1843 $collection = substr( $sisterKey, 10, strcspn( $sisterKey, ':}', 10 ) ); 1844 } else { 1845 $collection = 'internal'; 1846 } 1847 1848 return $collection; 1849 } 1850 1851 /** 1852 * @param float $age Age of volatile/interim key in seconds 1853 * @return bool Whether the age of a volatile value is negligible 1854 */ 1855 private function isVolatileValueAgeNegligible( $age ) { 1856 return ( $age < mt_rand( self::RECENT_SET_LOW_MS, self::RECENT_SET_HIGH_MS ) / 1e3 ); 1857 } 1858 1859 /** 1860 * Check whether set() is rate-limited to avoid concurrent I/O spikes 1861 * 1862 * This mitigates problems caused by popular keys suddenly becoming unavailable due to 1863 * unexpected evictions or cache server outages. These cases are not handled by the usual 1864 * preemptive refresh logic. 1865 * 1866 * With a typical scale-out infrastructure, CPU and query load from getWithSetCallback() 1867 * invocations is distributed among appservers and replica DBs, but cache operations for 1868 * a given key route to a single cache server (e.g. striped consistent hashing). A set() 1869 * stampede to a key can saturate the network link to its cache server. The intensity of 1870 * the problem is proportionate to the value size and access rate. The duration of the 1871 * problem is proportionate to value regeneration time. 1872 * 1873 * @param string $key Cache key made with makeKey()/makeGlobalKey() 1874 * @param string $kClass 1875 * @param mixed $value The regenerated value 1876 * @param float $elapsed Seconds spent fetching, validating, and regenerating the value 1877 * @param bool $hasLock Whether this thread has an exclusive regeneration lock 1878 * @return bool Whether it is OK to proceed with a key set operation 1879 */ 1880 private function checkAndSetCooloff( $key, $kClass, $value, $elapsed, $hasLock ) { 1881 $valueSisterKey = $this->makeSisterKey( $key, self::TYPE_VALUE, $this->onHostRoute ); 1882 list( $estimatedSize ) = $this->cache->setNewPreparedValues( [ 1883 $valueSisterKey => $value 1884 ] ); 1885 1886 if ( !$hasLock ) { 1887 // Suppose that this cache key is very popular (KEY_HIGH_QPS reads/second). 1888 // After eviction, there will be cache misses until it gets regenerated and saved. 1889 // If the time window when the key is missing lasts less than one second, then the 1890 // number of misses will not reach KEY_HIGH_QPS. This window largely corresponds to 1891 // the key regeneration time. Estimate the count/rate of cache misses, e.g.: 1892 // - 100 QPS, 20ms regeneration => ~2 misses (< 1s) 1893 // - 100 QPS, 100ms regeneration => ~10 misses (< 1s) 1894 // - 100 QPS, 3000ms regeneration => ~300 misses (100/s for 3s) 1895 $missesPerSecForHighQPS = ( min( $elapsed, 1 ) * $this->keyHighQps ); 1896 1897 // Determine whether there is enough I/O stampede risk to justify throttling set(). 1898 // Estimate unthrottled set() overhead, as bps, from miss count/rate and value size, 1899 // comparing it to the per-key uplink bps limit (KEY_HIGH_UPLINK_BPS), e.g.: 1900 // - 2 misses (< 1s), 10KB value, 1250000 bps limit => 160000 bits (low risk) 1901 // - 2 misses (< 1s), 100KB value, 1250000 bps limit => 1600000 bits (high risk) 1902 // - 10 misses (< 1s), 10KB value, 1250000 bps limit => 800000 bits (low risk) 1903 // - 10 misses (< 1s), 100KB value, 1250000 bps limit => 8000000 bits (high risk) 1904 // - 300 misses (100/s), 1KB value, 1250000 bps limit => 800000 bps (low risk) 1905 // - 300 misses (100/s), 10KB value, 1250000 bps limit => 8000000 bps (high risk) 1906 // - 300 misses (100/s), 100KB value, 1250000 bps limit => 80000000 bps (high risk) 1907 if ( ( $missesPerSecForHighQPS * $estimatedSize ) >= $this->keyHighUplinkBps ) { 1908 $cooloffSisterKey = $this->makeSisterKey( $key, self::TYPE_COOLOFF ); 1909 $this->cache->clearLastError(); 1910 if ( 1911 !$this->cache->add( $cooloffSisterKey, 1, self::COOLOFF_TTL ) && 1912 // Don't treat failures due to I/O errors as the key being in cooloff 1913 $this->cache->getLastError() === BagOStuff::ERR_NONE 1914 ) { 1915 $this->stats->increment( "wanobjectcache.$kClass.cooloff_bounce" ); 1916 1917 return false; 1918 } 1919 } 1920 } 1921 1922 // Corresponding metrics for cache writes that actually get sent over the write 1923 $this->stats->timing( "wanobjectcache.$kClass.regen_set_delay", 1e3 * $elapsed ); 1924 $this->stats->updateCount( "wanobjectcache.$kClass.regen_set_bytes", $estimatedSize ); 1925 1926 return true; 1927 } 1928 1929 /** 1930 * @param mixed $value 1931 * @param float|null $curTTL 1932 * @param array $curInfo 1933 * @param callable|null $touchedCallback 1934 * @return array (current time left or null, UNIX timestamp of last purge or null) 1935 * @note Callable type hints are not used to avoid class-autoloading 1936 */ 1937 private function resolveCTL( $value, $curTTL, $curInfo, $touchedCallback ) { 1938 if ( $touchedCallback === null || $value === false ) { 1939 return [ 1940 $curTTL, 1941 max( $curInfo[self::KEY_TOMB_AS_OF], $curInfo[self::KEY_CHECK_AS_OF] ) 1942 ]; 1943 } 1944 1945 $touched = $touchedCallback( $value ); 1946 if ( $touched !== null && $touched >= $curInfo[self::KEY_AS_OF] ) { 1947 $curTTL = min( $curTTL, self::TINY_NEGATIVE, $curInfo[self::KEY_AS_OF] - $touched ); 1948 } 1949 1950 return [ 1951 $curTTL, 1952 max( 1953 $curInfo[self::KEY_TOMB_AS_OF], 1954 $curInfo[self::KEY_CHECK_AS_OF], 1955 $touched 1956 ) 1957 ]; 1958 } 1959 1960 /** 1961 * @param mixed $value 1962 * @param float|null $lastPurge 1963 * @param callable|null $touchedCallback 1964 * @return float|null UNIX timestamp of last purge or null 1965 * @note Callable type hints are not used to avoid class-autoloading 1966 */ 1967 private function resolveTouched( $value, $lastPurge, $touchedCallback ) { 1968 return ( $touchedCallback === null || $value === false ) 1969 ? $lastPurge // nothing to derive the "touched timestamp" from 1970 : max( $touchedCallback( $value ), $lastPurge ); 1971 } 1972 1973 /** 1974 * @param string $key Cache key made with makeKey()/makeGlobalKey() 1975 * @param float $minAsOf Minimum acceptable "as of" timestamp 1976 * @return array (cached value or false, cache key metadata map) 1977 */ 1978 private function getInterimValue( $key, $minAsOf ) { 1979 $now = $this->getCurrentTime(); 1980 1981 if ( $this->useInterimHoldOffCaching ) { 1982 $wrapped = $this->cache->get( 1983 $this->makeSisterKey( $key, self::TYPE_INTERIM ) 1984 ); 1985 1986 list( $value, $keyInfo ) = $this->unwrap( $wrapped, $now ); 1987 if ( $this->isValid( $value, $keyInfo[self::KEY_AS_OF], $minAsOf ) ) { 1988 return [ $value, $keyInfo ]; 1989 } 1990 } 1991 1992 return $this->unwrap( false, $now ); 1993 } 1994 1995 /** 1996 * @param string $key Cache key made with makeKey()/makeGlobalKey() 1997 * @param mixed $value 1998 * @param int $ttl 1999 * @param int|null $version Value version number 2000 * @param float $walltime How long it took to generate the value in seconds 2001 */ 2002 private function setInterimValue( $key, $value, $ttl, $version, $walltime ) { 2003 $ttl = max( self::INTERIM_KEY_TTL, (int)$ttl ); 2004 2005 $wrapped = $this->wrap( $value, $ttl, $version, $this->getCurrentTime(), $walltime ); 2006 $this->cache->merge( 2007 $this->makeSisterKey( $key, self::TYPE_INTERIM ), 2008 static function () use ( $wrapped ) { 2009 return $wrapped; 2010 }, 2011 $ttl, 2012 1 2013 ); 2014 } 2015 2016 /** 2017 * @param mixed $busyValue 2018 * @return mixed 2019 */ 2020 private function resolveBusyValue( $busyValue ) { 2021 return ( $busyValue instanceof Closure ) ? $busyValue() : $busyValue; 2022 } 2023 2024 /** 2025 * Method to fetch multiple cache keys at once with regeneration 2026 * 2027 * This works the same as getWithSetCallback() except: 2028 * - a) The $keys argument must be the result of WANObjectCache::makeMultiKeys() 2029 * - b) The $callback argument must be a callback that takes the following arguments: 2030 * - $id: ID of the entity to query 2031 * - $oldValue: prior cache value or false if none was present 2032 * - &$ttl: reference to the TTL to be assigned to the new value (alterable) 2033 * - &$setOpts: reference to the new value set() options (alterable) 2034 * - $oldAsOf: generation UNIX timestamp of $oldValue or null if not present 2035 * - c) The return value is a map of (cache key => value) in the order of $keyedIds 2036 * 2037 * @see WANObjectCache::getWithSetCallback() 2038 * @see WANObjectCache::getMultiWithUnionSetCallback() 2039 * 2040 * Example usage: 2041 * @code 2042 * $rows = $cache->getMultiWithSetCallback( 2043 * // Map of cache keys to entity IDs 2044 * $cache->makeMultiKeys( 2045 * $this->fileVersionIds(), 2046 * function ( $id ) use ( $cache ) { 2047 * return $cache->makeKey( 'file-version', $id ); 2048 * } 2049 * ), 2050 * // Time-to-live (in seconds) 2051 * $cache::TTL_DAY, 2052 * // Function that derives the new key value 2053 * function ( $id, $oldValue, &$ttl, array &$setOpts ) { 2054 * $dbr = wfGetDB( DB_REPLICA ); 2055 * // Account for any snapshot/replica DB lag 2056 * $setOpts += Database::getCacheSetOptions( $dbr ); 2057 * 2058 * // Load the row for this file 2059 * $queryInfo = File::getQueryInfo(); 2060 * $row = $dbr->selectRow( 2061 * $queryInfo['tables'], 2062 * $queryInfo['fields'], 2063 * [ 'id' => $id ], 2064 * __METHOD__, 2065 * [], 2066 * $queryInfo['joins'] 2067 * ); 2068 * 2069 * return $row ? (array)$row : false; 2070 * }, 2071 * [ 2072 * // Process cache for 30 seconds 2073 * 'pcTTL' => 30, 2074 * // Use a dedicated 500 item cache (initialized on-the-fly) 2075 * 'pcGroup' => 'file-versions:500' 2076 * ] 2077 * ); 2078 * $files = array_map( [ __CLASS__, 'newFromRow' ], $rows ); 2079 * @endcode 2080 * 2081 * @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys() 2082 * @param int $ttl Seconds to live for key updates 2083 * @param callable $callback Callback the yields entity regeneration callbacks 2084 * @param array $opts Options map 2085 * @return mixed[] Map of (cache key => value) in the same order as $keyedIds 2086 * @since 1.28 2087 */ 2088 final public function getMultiWithSetCallback( 2089 ArrayIterator $keyedIds, $ttl, callable $callback, array $opts = [] 2090 ) { 2091 // Batch load required keys into the in-process warmup cache 2092 $this->warmupCache = $this->fetchWrappedValuesForWarmupCache( 2093 $this->getNonProcessCachedMultiKeys( $keyedIds, $opts ), 2094 $opts['checkKeys'] ?? [] 2095 ); 2096 $this->warmupKeyMisses = 0; 2097 2098 // The required callback signature includes $id as the first argument for convenience 2099 // to distinguish different items. To reuse the code in getWithSetCallback(), wrap the 2100 // callback with a proxy callback that has the standard getWithSetCallback() signature. 2101 // This is defined only once per batch to avoid closure creation overhead. 2102 $proxyCb = static function ( $oldValue, &$ttl, &$setOpts, $oldAsOf, $params ) 2103 use ( $callback ) 2104 { 2105 return $callback( $params['id'], $oldValue, $ttl, $setOpts, $oldAsOf ); 2106 }; 2107 2108 $values = []; 2109 foreach ( $keyedIds as $key => $id ) { // preserve order 2110 $values[$key] = $this->getWithSetCallback( 2111 $key, 2112 $ttl, 2113 $proxyCb, 2114 $opts, 2115 [ 'id' => $id ] 2116 ); 2117 } 2118 2119 $this->warmupCache = []; 2120 2121 return $values; 2122 } 2123 2124 /** 2125 * Method to fetch/regenerate multiple cache keys at once 2126 * 2127 * This works the same as getWithSetCallback() except: 2128 * - a) The $keys argument expects the result of WANObjectCache::makeMultiKeys() 2129 * - b) The $callback argument expects a callback returning a map of (ID => new value) 2130 * for all entity IDs in $ids and it takes the following arguments: 2131 * - $ids: list of entity IDs that require cache regeneration 2132 * - &$ttls: reference to the (entity ID => new TTL) map (alterable) 2133 * - &$setOpts: reference to the new value set() options (alterable) 2134 * - c) The return value is a map of (cache key => value) in the order of $keyedIds 2135 * - d) The "lockTSE" and "busyValue" options are ignored 2136 * 2137 * @see WANObjectCache::getWithSetCallback() 2138 * @see WANObjectCache::getMultiWithSetCallback() 2139 * 2140 * Example usage: 2141 * @code 2142 * $rows = $cache->getMultiWithUnionSetCallback( 2143 * // Map of cache keys to entity IDs 2144 * $cache->makeMultiKeys( 2145 * $this->fileVersionIds(), 2146 * function ( $id ) use ( $cache ) { 2147 * return $cache->makeKey( 'file-version', $id ); 2148 * } 2149 * ), 2150 * // Time-to-live (in seconds) 2151 * $cache::TTL_DAY, 2152 * // Function that derives the new key value 2153 * function ( array $ids, array &$ttls, array &$setOpts ) { 2154 * $dbr = wfGetDB( DB_REPLICA ); 2155 * // Account for any snapshot/replica DB lag 2156 * $setOpts += Database::getCacheSetOptions( $dbr ); 2157 * 2158 * // Load the rows for these files 2159 * $rows = []; 2160 * $queryInfo = File::getQueryInfo(); 2161 * $res = $dbr->select( 2162 * $queryInfo['tables'], 2163 * $queryInfo['fields'], 2164 * [ 'id' => $ids ], 2165 * __METHOD__, 2166 * [], 2167 * $queryInfo['joins'] 2168 * ); 2169 * foreach ( $res as $row ) { 2170 * $rows[$row->id] = $row; 2171 * $mtime = wfTimestamp( TS_UNIX, $row->timestamp ); 2172 * $ttls[$row->id] = $this->adaptiveTTL( $mtime, $ttls[$row->id] ); 2173 * } 2174 * 2175 * return $rows; 2176 * }, 2177 * ] 2178 * ); 2179 * $files = array_map( [ __CLASS__, 'newFromRow' ], $rows ); 2180 * @endcode 2181 * 2182 * @param ArrayIterator $keyedIds Result of WANObjectCache::makeMultiKeys() 2183 * @param int $ttl Seconds to live for key updates 2184 * @param callable $callback Callback the yields entity regeneration callbacks 2185 * @param array $opts Options map 2186 * @return mixed[] Map of (cache key => value) in the same order as $keyedIds 2187 * @since 1.30 2188 */ 2189 final public function getMultiWithUnionSetCallback( 2190 ArrayIterator $keyedIds, $ttl, callable $callback, array $opts = [] 2191 ) { 2192 $checkKeys = $opts['checkKeys'] ?? []; 2193 unset( $opts['lockTSE'] ); // incompatible 2194 unset( $opts['busyValue'] ); // incompatible 2195 2196 // Batch load required keys into the in-process warmup cache 2197 $keysByIdGet = $this->getNonProcessCachedMultiKeys( $keyedIds, $opts ); 2198 $this->warmupCache = $this->fetchWrappedValuesForWarmupCache( $keysByIdGet, $checkKeys ); 2199 $this->warmupKeyMisses = 0; 2200 2201 // IDs of entities known to be in need of regeneration 2202 $idsRegen = []; 2203 2204 // Find out which keys are missing/deleted/stale 2205 $resByKey = $this->fetchKeys( $keysByIdGet, $checkKeys ); 2206 foreach ( $keysByIdGet as $id => $key ) { 2207 $res = $resByKey[$key]; 2208 $value = $res[self::RES_VALUE]; 2209 $metadata = $res[self::RES_METADATA]; 2210 if ( $value === false || $metadata[self::KEY_CUR_TTL] < 0 ) { 2211 $idsRegen[] = $id; 2212 } 2213 } 2214 2215 // Run the callback to populate the regeneration value map for all required IDs 2216 $newSetOpts = []; 2217 $newTTLsById = array_fill_keys( $idsRegen, $ttl ); 2218 $newValsById = $idsRegen ? $callback( $idsRegen, $newTTLsById, $newSetOpts ) : []; 2219 2220 // The required callback signature includes $id as the first argument for convenience 2221 // to distinguish different items. To reuse the code in getWithSetCallback(), wrap the 2222 // callback with a proxy callback that has the standard getWithSetCallback() signature. 2223 // This is defined only once per batch to avoid closure creation overhead. 2224 $proxyCb = static function ( $oldValue, &$ttl, &$setOpts, $oldAsOf, $params ) 2225 use ( $callback, $newValsById, $newTTLsById, $newSetOpts ) 2226 { 2227 $id = $params['id']; 2228 2229 if ( array_key_exists( $id, $newValsById ) ) { 2230 // Value was already regerated as expected, so use the value in $newValsById 2231 $newValue = $newValsById[$id]; 2232 $ttl = $newTTLsById[$id]; 2233 $setOpts = $newSetOpts; 2234 } else { 2235 // Pre-emptive/popularity refresh and version mismatch cases are not detected 2236 // above and thus $newValsById has no entry. Run $callback on this single entity. 2237 $ttls = [ $id => $ttl ]; 2238 $newValue = $callback( [ $id ], $ttls, $setOpts )[$id]; 2239 $ttl = $ttls[$id]; 2240 } 2241 2242 return $newValue; 2243 }; 2244 2245 // Run the cache-aside logic using warmupCache instead of persistent cache queries 2246 $values = []; 2247 foreach ( $keyedIds as $key => $id ) { // preserve order 2248 $values[$key] = $this->getWithSetCallback( 2249 $key, 2250 $ttl, 2251 $proxyCb, 2252 $opts, 2253 [ 'id' => $id ] 2254 ); 2255 } 2256 2257 $this->warmupCache = []; 2258 2259 return $values; 2260 } 2261 2262 /** 2263 * Set a key to soon expire in the local cluster if it pre-dates $purgeTimestamp 2264 * 2265 * This sets stale keys' time-to-live at HOLDOFF_TTL seconds, which both avoids 2266 * broadcasting in mcrouter setups and also avoids races with new tombstones. 2267 * 2268 * @param string $key Cache key made with makeKey()/makeGlobalKey() 2269 * @param int $purgeTimestamp UNIX timestamp of purge 2270 * @param bool &$isStale Whether the key is stale 2271 * @return bool Success 2272 * @since 1.28 2273 */ 2274 final public function reap( $key, $purgeTimestamp, &$isStale = false ) { 2275 $valueSisterKey = $this->makeSisterKey( $key, self::TYPE_VALUE ); 2276 2277 $minAsOf = $purgeTimestamp + self::HOLDOFF_TTL; 2278 $wrapped = $this->cache->get( $valueSisterKey ); 2279 if ( is_array( $wrapped ) && $wrapped[self::FLD_TIME] < $minAsOf ) { 2280 $isStale = true; 2281 $this->logger->warning( "Reaping stale value key '$key'." ); 2282 $ttlReap = self::HOLDOFF_TTL; // avoids races with tombstone creation 2283 $ok = $this->cache->changeTTL( $valueSisterKey, $ttlReap ); 2284 if ( !$ok ) { 2285 $this->logger->error( "Could not complete reap of key '$key'." ); 2286 } 2287 2288 return $ok; 2289 } 2290 2291 $isStale = false; 2292 2293 return true; 2294 } 2295 2296 /** 2297 * Set a "check" key to soon expire in the local cluster if it pre-dates $purgeTimestamp 2298 * 2299 * @param string $key Cache key made with makeKey()/makeGlobalKey() 2300 * @param int $purgeTimestamp UNIX timestamp of purge 2301 * @param bool &$isStale Whether the key is stale 2302 * @return bool Success 2303 * @since 1.28 2304 */ 2305 final public function reapCheckKey( $key, $purgeTimestamp, &$isStale = false ) { 2306 $checkSisterKey = $this->makeSisterKey( $key, self::TYPE_TIMESTAMP ); 2307 2308 $wrapped = $this->cache->get( $checkSisterKey ); 2309 $purge = $this->parsePurgeValue( $wrapped ); 2310 if ( $purge && $purge[self::PURGE_TIME] < $purgeTimestamp ) { 2311 $isStale = true; 2312 $this->logger->warning( "Reaping stale check key '$key'." ); 2313 $ok = $this->cache->changeTTL( $checkSisterKey, self::TTL_SECOND ); 2314 if ( !$ok ) { 2315 $this->logger->error( "Could not complete reap of check key '$key'." ); 2316 } 2317 2318 return $ok; 2319 } 2320 2321 $isStale = false; 2322 2323 return false; 2324 } 2325 2326 /** 2327 * Make a cache key for the global keyspace and given components 2328 * 2329 * @see IStoreKeyEncoder::makeGlobalKey() 2330 * 2331 * @param string $collection Key collection name component 2332 * @param string|int ...$components Additional, ordered, key components for entity IDs 2333 * @return string Colon-separated, keyspace-prepended, ordered list of encoded components 2334 * @since 1.27 2335 */ 2336 public function makeGlobalKey( $collection, ...$components ) { 2337 return $this->cache->makeGlobalKey( ...func_get_args() ); 2338 } 2339 2340 /** 2341 * Make a cache key using the "global" keyspace for the given components 2342 * 2343 * @see IStoreKeyEncoder::makeKey() 2344 * 2345 * @param string $collection Key collection name component 2346 * @param string|int ...$components Additional, ordered, key components for entity IDs 2347 * @return string Colon-separated, keyspace-prepended, ordered list of encoded components 2348 * @since 1.27 2349 */ 2350 public function makeKey( $collection, ...$components ) { 2351 return $this->cache->makeKey( ...func_get_args() ); 2352 } 2353 2354 /** 2355 * Hash a possibly long string into a suitable component for makeKey()/makeGlobalKey() 2356 * 2357 * @param string $component A raw component used in building a cache key 2358 * @return string 64 character HMAC using a stable secret for public collision resistance 2359 * @since 1.34 2360 */ 2361 public function hash256( $component ) { 2362 return hash_hmac( 'sha256', $component, $this->secret ); 2363 } 2364 2365 /** 2366 * Get an iterator of (cache key => entity ID) for a list of entity IDs 2367 * 2368 * The callback takes an ID string and returns a key via makeKey()/makeGlobalKey(). 2369 * There should be no network nor filesystem I/O used in the callback. The entity 2370 * ID/key mapping must be 1:1 or an exception will be thrown. If hashing is needed, 2371 * then use the hash256() method. 2372 * 2373 * Example usage for the default keyspace: 2374 * @code 2375 * $keyedIds = $cache->makeMultiKeys( 2376 * $modules, 2377 * function ( $module ) use ( $cache ) { 2378 * return $cache->makeKey( 'module-info', $module ); 2379 * } 2380 * ); 2381 * @endcode 2382 * 2383 * Example usage for mixed default and global keyspace: 2384 * @code 2385 * $keyedIds = $cache->makeMultiKeys( 2386 * $filters, 2387 * function ( $filter ) use ( $cache ) { 2388 * return ( strpos( $filter, 'central:' ) === 0 ) 2389 * ? $cache->makeGlobalKey( 'regex-filter', $filter ) 2390 * : $cache->makeKey( 'regex-filter', $filter ) 2391 * } 2392 * ); 2393 * @endcode 2394 * 2395 * Example usage with hashing: 2396 * @code 2397 * $keyedIds = $cache->makeMultiKeys( 2398 * $urls, 2399 * function ( $url ) use ( $cache ) { 2400 * return $cache->makeKey( 'url-info', $cache->hash256( $url ) ); 2401 * } 2402 * ); 2403 * @endcode 2404 * 2405 * @see WANObjectCache::makeKey() 2406 * @see WANObjectCache::makeGlobalKey() 2407 * @see WANObjectCache::hash256() 2408 * 2409 * @param string[]|int[] $ids List of entity IDs 2410 * @param callable $keyCallback Function returning makeKey()/makeGlobalKey() on the input ID 2411 * @return ArrayIterator Iterator of (cache key => ID); order of $ids is preserved 2412 * @throws UnexpectedValueException 2413 * @since 1.28 2414 */ 2415 final public function makeMultiKeys( array $ids, $keyCallback ) { 2416 $idByKey = []; 2417 foreach ( $ids as $id ) { 2418 // Discourage triggering of automatic makeKey() hashing in some backends 2419 if ( strlen( $id ) > 64 ) { 2420 $this->logger->warning( __METHOD__ . ": long ID '$id'; use hash256()" ); 2421 } 2422 $key = $keyCallback( $id, $this ); 2423 // Edge case: ignore key collisions due to duplicate $ids like "42" and 42 2424 if ( !isset( $idByKey[$key] ) ) { 2425 $idByKey[$key] = $id; 2426 } elseif ( (string)$id !== (string)$idByKey[$key] ) { 2427 throw new UnexpectedValueException( 2428 "Cache key collision; IDs ('$id','{$idByKey[$key]}') map to '$key'" 2429 ); 2430 } 2431 } 2432 2433 return new ArrayIterator( $idByKey ); 2434 } 2435 2436 /** 2437 * Get an (ID => value) map from (i) a non-unique list of entity IDs, and (ii) the list 2438 * of corresponding entity values by first appearance of each ID in the entity ID list 2439 * 2440 * For use with getMultiWithSetCallback() and getMultiWithUnionSetCallback(). 2441 * 2442 * *Only* use this method if the entity ID/key mapping is trivially 1:1 without exception. 2443 * Key generation method must utitilize the *full* entity ID in the key (not a hash of it). 2444 * 2445 * Example usage: 2446 * @code 2447 * $poems = $cache->getMultiWithSetCallback( 2448 * $cache->makeMultiKeys( 2449 * $uuids, 2450 * function ( $uuid ) use ( $cache ) { 2451 * return $cache->makeKey( 'poem', $uuid ); 2452 * } 2453 * ), 2454 * $cache::TTL_DAY, 2455 * function ( $uuid ) use ( $url ) { 2456 * return $this->http->run( [ 'method' => 'GET', 'url' => "$url/$uuid" ] ); 2457 * } 2458 * ); 2459 * $poemsByUUID = $cache->multiRemap( $uuids, $poems ); 2460 * @endcode 2461 * 2462 * @see WANObjectCache::makeMultiKeys() 2463 * @see WANObjectCache::getMultiWithSetCallback() 2464 * @see WANObjectCache::getMultiWithUnionSetCallback() 2465 * 2466 * @param string[]|int[] $ids Entity ID list makeMultiKeys() 2467 * @param mixed[] $res Result of getMultiWithSetCallback()/getMultiWithUnionSetCallback() 2468 * @return mixed[] Map of (ID => value); order of $ids is preserved 2469 * @since 1.34 2470 */ 2471 final public function multiRemap( array $ids, array $res ) { 2472 if ( count( $ids ) !== count( $res ) ) { 2473 // If makeMultiKeys() is called on a list of non-unique IDs, then the resulting 2474 // ArrayIterator will have less entries due to "first appearance" de-duplication 2475 $ids = array_keys( array_flip( $ids ) ); 2476 if ( count( $ids ) !== count( $res ) ) { 2477 throw new UnexpectedValueException( "Multi-key result does not match ID list" ); 2478 } 2479 } 2480 2481 return array_combine( $ids, $res ); 2482 } 2483 2484 /** 2485 * Get the "last error" registered; clearLastError() should be called manually 2486 * @return int ERR_* class constant for the "last error" registry 2487 */ 2488 final public function getLastError() { 2489 $code = $this->cache->getLastError(); 2490 switch ( $code ) { 2491 case BagOStuff::ERR_NONE: 2492 return self::ERR_NONE; 2493 case BagOStuff::ERR_NO_RESPONSE: 2494 return self::ERR_NO_RESPONSE; 2495 case BagOStuff::ERR_UNREACHABLE: 2496 return self::ERR_UNREACHABLE; 2497 default: 2498 return self::ERR_UNEXPECTED; 2499 } 2500 } 2501 2502 /** 2503 * Clear the "last error" registry 2504 */ 2505 final public function clearLastError() { 2506 $this->cache->clearLastError(); 2507 } 2508 2509 /** 2510 * Clear the in-process caches; useful for testing 2511 * 2512 * @since 1.27 2513 */ 2514 public function clearProcessCache() { 2515 $this->processCaches = []; 2516 } 2517 2518 /** 2519 * Enable or disable the use of brief caching for tombstoned keys 2520 * 2521 * When a key is purged via delete(), there normally is a period where caching 2522 * is hold-off limited to an extremely short time. This method will disable that 2523 * caching, forcing the callback to run for any of: 2524 * - WANObjectCache::getWithSetCallback() 2525 * - WANObjectCache::getMultiWithSetCallback() 2526 * - WANObjectCache::getMultiWithUnionSetCallback() 2527 * 2528 * This is useful when both: 2529 * - a) the database used by the callback is known to be up-to-date enough 2530 * for some particular purpose (e.g. replica DB has applied transaction X) 2531 * - b) the caller needs to exploit that fact, and therefore needs to avoid the 2532 * use of inherently volatile and possibly stale interim keys 2533 * 2534 * @see WANObjectCache::delete() 2535 * @param bool $enabled Whether to enable interim caching 2536 * @since 1.31 2537 */ 2538 final public function useInterimHoldOffCaching( $enabled ) { 2539 $this->useInterimHoldOffCaching = $enabled; 2540 } 2541 2542 /** 2543 * @param int $flag ATTR_* class constant 2544 * @return int QOS_* class constant 2545 * @since 1.28 2546 */ 2547 public function getQoS( $flag ) { 2548 return $this->cache->getQoS( $flag ); 2549 } 2550 2551 /** 2552 * Get a TTL that is higher for objects that have not changed recently 2553 * 2554 * This is useful for keys that get explicit purges and DB or purge relay 2555 * lag is a potential concern (especially how it interacts with CDN cache) 2556 * 2557 * Example usage: 2558 * @code 2559 * // Last-modified time of page 2560 * $mtime = wfTimestamp( TS_UNIX, $page->getTimestamp() ); 2561 * // Get adjusted TTL. If $mtime is 3600 seconds ago and $minTTL/$factor left at 2562 * // defaults, then $ttl is 3600 * .2 = 720. If $minTTL was greater than 720, then 2563 * // $ttl would be $minTTL. If $maxTTL was smaller than 720, $ttl would be $maxTTL. 2564 * $ttl = $cache->adaptiveTTL( $mtime, $cache::TTL_DAY ); 2565 * @endcode 2566 * 2567 * Another use case is when there are no applicable "last modified" fields in the DB, 2568 * and there are too many dependencies for explicit purges to be viable, and the rate of 2569 * change to relevant content is unstable, and it is highly valued to have the cached value 2570 * be as up-to-date as possible. 2571 * 2572 * Example usage: 2573 * @code 2574 * $query = "<some complex query>"; 2575 * $idListFromComplexQuery = $cache->getWithSetCallback( 2576 * $cache->makeKey( 'complex-graph-query', $hashOfQuery ), 2577 * GraphQueryClass::STARTING_TTL, 2578 * function ( $oldValue, &$ttl, array &$setOpts, $oldAsOf ) use ( $query, $cache ) { 2579 * $gdb = $this->getReplicaGraphDbConnection(); 2580 * // Account for any snapshot/replica DB lag 2581 * $setOpts += GraphDatabase::getCacheSetOptions( $gdb ); 2582 * 2583 * $newList = iterator_to_array( $gdb->query( $query ) ); 2584 * sort( $newList, SORT_NUMERIC ); // normalize 2585 * 2586 * $minTTL = GraphQueryClass::MIN_TTL; 2587 * $maxTTL = GraphQueryClass::MAX_TTL; 2588 * if ( $oldValue !== false ) { 2589 * // Note that $oldAsOf is the last time this callback ran 2590 * $ttl = ( $newList === $oldValue ) 2591 * // No change: cache for 150% of the age of $oldValue 2592 * ? $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, 1.5 ) 2593 * // Changed: cache for 50% of the age of $oldValue 2594 * : $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, .5 ); 2595 * } 2596 * 2597 * return $newList; 2598 * }, 2599 * [ 2600 * // Keep stale values around for doing comparisons for TTL calculations. 2601 * // High values improve long-tail keys hit-rates, though might waste space. 2602 * 'staleTTL' => GraphQueryClass::GRACE_TTL 2603 * ] 2604 * ); 2605 * @endcode 2606 * 2607 * @param int|float $mtime UNIX timestamp 2608 * @param int $maxTTL Maximum TTL (seconds) 2609 * @param int $minTTL Minimum TTL (seconds); Default: 30 2610 * @param float $factor Value in the range (0,1); Default: .2 2611 * @return int Adaptive TTL 2612 * @since 1.28 2613 */ 2614 public function adaptiveTTL( $mtime, $maxTTL, $minTTL = 30, $factor = 0.2 ) { 2615 if ( is_float( $mtime ) || ctype_digit( $mtime ) ) { 2616 $mtime = (int)$mtime; // handle fractional seconds and string integers 2617 } 2618 2619 if ( !is_int( $mtime ) || $mtime <= 0 ) { 2620 return $minTTL; // no last-modified time provided 2621 } 2622 2623 $age = $this->getCurrentTime() - $mtime; 2624 2625 return (int)min( $maxTTL, max( $minTTL, $factor * $age ) ); 2626 } 2627 2628 /** 2629 * @return int Number of warmup key cache misses last round 2630 * @since 1.30 2631 */ 2632 final public function getWarmupKeyMisses() { 2633 return $this->warmupKeyMisses; 2634 } 2635 2636 /** 2637 * Set a sister key to a purge value in all datacenters 2638 * 2639 * This method should not wait for the operation to complete on remote datacenters 2640 * 2641 * Since older purge values can sometimes arrive after newer ones, use a relative expiry 2642 * so that even if the older value replaces the newer value, the TTL will greater than the 2643 * remaining TTL on the older value (assuming that all purges for a key use the same TTL). 2644 * 2645 * @param array<string,string> $purgeBySisterKey Map of 2646 * (sister key => result of makeTombstonePurgeValue()/makeCheckKeyPurgeValue()) 2647 * @param int $ttl Seconds to keep the purge value around 2648 * @return bool Success 2649 */ 2650 protected function relayVolatilePurges( array $purgeBySisterKey, int $ttl ) { 2651 $purgeByRouteKey = []; 2652 foreach ( $purgeBySisterKey as $sisterKey => $purge ) { 2653 if ( $this->broadcastRoute !== null ) { 2654 $routeKey = $this->prependRoute( $sisterKey, $this->broadcastRoute ); 2655 } else { 2656 $routeKey = $sisterKey; 2657 } 2658 $purgeByRouteKey[$routeKey] = $purge; 2659 } 2660 2661 if ( count( $purgeByRouteKey ) == 1 ) { 2662 $purge = reset( $purgeByRouteKey ); 2663 $ok = $this->cache->set( key( $purgeByRouteKey ), $purge, $ttl ); 2664 } else { 2665 $ok = $this->cache->setMulti( $purgeByRouteKey, $ttl ); 2666 } 2667 2668 return $ok; 2669 } 2670 2671 /** 2672 * Remove a sister key from all datacenters 2673 * 2674 * This method should not wait for the operation to complete on remote datacenters 2675 * 2676 * @param string $sisterKey A value, "check", or flux sister key 2677 * @return bool Success 2678 */ 2679 protected function relayNonVolatilePurge( string $sisterKey ) { 2680 if ( $this->broadcastRoute !== null ) { 2681 $routeKey = $this->prependRoute( $sisterKey, $this->broadcastRoute ); 2682 } else { 2683 $routeKey = $sisterKey; 2684 } 2685 2686 return $this->cache->delete( $routeKey ); 2687 } 2688 2689 /** 2690 * @param string $sisterKey Sister key 2691 * @param string $route Key routing prefix 2692 * @return string 2693 */ 2694 protected function prependRoute( string $sisterKey, string $route ) { 2695 if ( $sisterKey[0] === '/' ) { 2696 throw new RuntimeException( "Sister key '$sisterKey' already contains a route." ); 2697 } 2698 2699 return $route . $sisterKey; 2700 } 2701 2702 /** 2703 * Schedule a deferred cache regeneration if possible 2704 * 2705 * @param string $key Cache key made with makeKey()/makeGlobalKey() 2706 * @param int $ttl Seconds to live 2707 * @param callable $callback 2708 * @param array $opts 2709 * @param array $cbParams 2710 * @return bool Success 2711 * @note Callable type hints are not used to avoid class-autoloading 2712 */ 2713 private function scheduleAsyncRefresh( $key, $ttl, $callback, array $opts, array $cbParams ) { 2714 if ( !$this->asyncHandler ) { 2715 return false; 2716 } 2717 // Update the cache value later, such during post-send of an HTTP request. This forces 2718 // cache regeneration by setting "minAsOf" to infinity, meaning that no existing value 2719 // is considered valid. Furthermore, note that preemptive regeneration is not applicable 2720 // to invalid values, so there is no risk of infinite preemptive regeneration loops. 2721 $func = $this->asyncHandler; 2722 $func( function () use ( $key, $ttl, $callback, $opts, $cbParams ) { 2723 $opts['minAsOf'] = INF; 2724 try { 2725 $this->fetchOrRegenerate( $key, $ttl, $callback, $opts, $cbParams ); 2726 } catch ( Exception $e ) { 2727 // Log some context for easier debugging 2728 $this->logger->error( 'Async refresh failed for {key}', [ 2729 'key' => $key, 2730 'ttl' => $ttl, 2731 'exception' => $e 2732 ] ); 2733 throw $e; 2734 } 2735 } ); 2736 2737 return true; 2738 } 2739 2740 /** 2741 * Check if a key is fresh or in the grace window and thus due for randomized reuse 2742 * 2743 * If $curTTL > 0 (e.g. value not expired) then this returns true. If $curTTL <= -$graceTTL 2744 * (e.g. value out of grace) then this returns false. Otherwise, the chance of this 2745 * returning true decreases steadily from 100% to 0% as the |$curTTL| moves from 0 to 2746 * $graceTTL seconds. 2747 * 2748 * This approach handles widely varying levels of cache access traffic. 2749 * 2750 * @param float $curTTL Approximate TTL left on the key 2751 * @param int $graceTTL Consider using stale values if $curTTL is greater than this 2752 * @return bool 2753 */ 2754 private function isAliveOrInGracePeriod( $curTTL, $graceTTL ) { 2755 if ( $curTTL > 0 ) { 2756 return true; 2757 } elseif ( $graceTTL <= 0 ) { 2758 return false; 2759 } 2760 2761 $ageStale = abs( $curTTL ); // seconds of staleness 2762 $curGraceTTL = ( $graceTTL - $ageStale ); // current grace-time-to-live 2763 if ( $curGraceTTL <= 0 ) { 2764 return false; // already out of grace period 2765 } 2766 2767 // Chance of using a stale value is the complement of the chance of refreshing it 2768 return !$this->worthRefreshExpiring( $curGraceTTL, $graceTTL, $graceTTL ); 2769 } 2770 2771 /** 2772 * Check if a key is nearing expiration and thus due for randomized regeneration 2773 * 2774 * If $curTTL is greater than the "low" threshold (e.g. not nearing expiration) then this 2775 * returns false. If $curTTL <= 0 (e.g. value already expired), then this returns false. 2776 * Otherwise, the chance of this returning true increases steadily from 0% to 100% as 2777 * $curTTL moves from the "low" threshold down to 0 seconds. 2778 * 2779 * This approach handles widely varying levels of cache access traffic. 2780 * 2781 * The logical TTL will be used as the "low" threshold if it is less than $lowTTL. 2782 * 2783 * @param float $curTTL Approximate TTL left on the key 2784 * @param float $logicalTTL Full logical TTL assigned to the key 2785 * @param float $lowTTL Consider a refresh when $curTTL is less than this; the "low" threshold 2786 * @return bool 2787 */ 2788 protected function worthRefreshExpiring( $curTTL, $logicalTTL, $lowTTL ) { 2789 if ( $lowTTL <= 0 ) { 2790 return false; 2791 } 2792 2793 // T264787: avoid having keys start off with a high chance of being refreshed; 2794 // the point where refreshing becomes possible cannot precede the key lifetime. 2795 $effectiveLowTTL = min( $lowTTL, $logicalTTL ?: INF ); 2796 2797 if ( $curTTL >= $effectiveLowTTL || $curTTL <= 0 ) { 2798 return false; 2799 } 2800 2801 $chance = ( 1 - $curTTL / $effectiveLowTTL ); 2802 2803 // @phan-suppress-next-line PhanTypeMismatchArgumentInternal 2804 $decision = ( mt_rand( 1, 1e9 ) <= 1e9 * $chance ); 2805 2806 $this->logger->debug( 2807 "worthRefreshExpiring($curTTL, $logicalTTL, $lowTTL): " . 2808 "p = $chance; refresh = " . ( $decision ? 'Y' : 'N' ) 2809 ); 2810 2811 return $decision; 2812 } 2813 2814 /** 2815 * Check if a key is due for randomized regeneration due to its popularity 2816 * 2817 * This is used so that popular keys can preemptively refresh themselves for higher 2818 * consistency (especially in the case of purge loss/delay). Unpopular keys can remain 2819 * in cache with their high nominal TTL. This means popular keys keep good consistency, 2820 * whether the data changes frequently or not, and long-tail keys get to stay in cache 2821 * and get hits too. Similar to worthRefreshExpiring(), randomization is used. 2822 * 2823 * @param float $asOf UNIX timestamp of the value 2824 * @param int $ageNew Age of key when this might recommend refreshing (seconds) 2825 * @param int $timeTillRefresh Age of key when it should be refreshed if popular (seconds) 2826 * @param float $now The current UNIX timestamp 2827 * @return bool 2828 */ 2829 protected function worthRefreshPopular( $asOf, $ageNew, $timeTillRefresh, $now ) { 2830 if ( $ageNew < 0 || $timeTillRefresh <= 0 ) { 2831 return false; 2832 } 2833 2834 $age = $now - $asOf; 2835 $timeOld = $age - $ageNew; 2836 if ( $timeOld <= 0 ) { 2837 return false; 2838 } 2839 2840 $popularHitsPerSec = 1; 2841 // Lifecycle is: new, ramp-up refresh chance, full refresh chance. 2842 // Note that the "expected # of refreshes" for the ramp-up time range is half 2843 // of what it would be if P(refresh) was at its full value during that time range. 2844 $refreshWindowSec = max( $timeTillRefresh - $ageNew - self::RAMPUP_TTL / 2, 1 ); 2845 // P(refresh) * (# hits in $refreshWindowSec) = (expected # of refreshes) 2846 // P(refresh) * ($refreshWindowSec * $popularHitsPerSec) = 1 (by definition) 2847 // P(refresh) = 1/($refreshWindowSec * $popularHitsPerSec) 2848 $chance = 1 / ( $popularHitsPerSec * $refreshWindowSec ); 2849 // Ramp up $chance from 0 to its nominal value over RAMPUP_TTL seconds to avoid stampedes 2850 $chance *= ( $timeOld <= self::RAMPUP_TTL ) ? $timeOld / self::RAMPUP_TTL : 1; 2851 2852 // @phan-suppress-next-line PhanTypeMismatchArgumentInternal 2853 $decision = ( mt_rand( 1, 1e9 ) <= 1e9 * $chance ); 2854 2855 $this->logger->debug( 2856 "worthRefreshPopular($asOf, $ageNew, $timeTillRefresh, $now): " . 2857 "p = $chance; refresh = " . ( $decision ? 'Y' : 'N' ) 2858 ); 2859 2860 return $decision; 2861 } 2862 2863 /** 2864 * Check if $value is not false, versioned (if needed), and not older than $minTime (if set) 2865 * 2866 * @param array|bool $value 2867 * @param float $asOf The time $value was generated 2868 * @param float $minAsOf Minimum acceptable "as of" timestamp 2869 * @param float|null $purgeTime The last time the value was invalidated 2870 * @return bool 2871 */ 2872 protected function isValid( $value, $asOf, $minAsOf, $purgeTime = null ) { 2873 // Avoid reading any key not generated after the latest delete() or touch 2874 $safeMinAsOf = max( $minAsOf, $purgeTime + self::TINY_POSTIVE ); 2875 2876 if ( $value === false ) { 2877 return false; 2878 } elseif ( $safeMinAsOf > 0 && $asOf < $minAsOf ) { 2879 return false; 2880 } 2881 2882 return true; 2883 } 2884 2885 /** 2886 * @param mixed $value 2887 * @param int $ttl Seconds to live or zero for "indefinite" 2888 * @param int|null $version Value version number or null if not versioned 2889 * @param float $now Unix Current timestamp just before calling set() 2890 * @param float|null $walltime How long it took to generate the value in seconds 2891 * @return array 2892 */ 2893 private function wrap( $value, $ttl, $version, $now, $walltime ) { 2894 // Returns keys in ascending integer order for PHP7 array packing: 2895 // https://nikic.github.io/2014/12/22/PHPs-new-hashtable-implementation.html 2896 $wrapped = [ 2897 self::FLD_FORMAT_VERSION => self::VERSION, 2898 self::FLD_VALUE => $value, 2899 self::FLD_TTL => $ttl, 2900 self::FLD_TIME => $now 2901 ]; 2902 if ( $version !== null ) { 2903 $wrapped[self::FLD_VALUE_VERSION] = $version; 2904 } 2905 if ( $walltime >= self::GENERATION_SLOW_SEC ) { 2906 $wrapped[self::FLD_GENERATION_TIME] = $walltime; 2907 } 2908 2909 return $wrapped; 2910 } 2911 2912 /** 2913 * @param array|string|false $wrapped The entry at a cache key (false if key is nonexistant) 2914 * @param float $now Unix Current timestamp (preferrably pre-query) 2915 * @return array<mixed,array> (value or false if absent/tombstoned/malformed, metadata map). 2916 * The cache key metadata map includes the following metadata: 2917 * - WANObjectCache::KEY_VERSION: value version number; null if there is no value 2918 * - WANObjectCache::KEY_AS_OF: value generation timestamp (UNIX); null if there is no value 2919 * - WANObjectCache::KEY_TTL: assigned logical TTL (seconds); null if there is no value 2920 * - WANObjectCache::KEY_CUR_TTL: remaining logical TTL (seconds) (negative if tombstoned) 2921 * - WANObjectCache::KEY_TOMB_AS_OF: tombstone timestamp (UNIX); null if not tombstoned 2922 * @phan-return array{0:mixed,1:array{version:?mixed,asOf:?mixed,ttl:?int|float,curTTL:?int|float,tombAsOf:?mixed}} 2923 */ 2924 private function unwrap( $wrapped, $now ) { 2925 $value = false; 2926 $info = $this->newKeyInfoPlaceholder(); 2927 2928 if ( is_array( $wrapped ) ) { 2929 // Entry expected to be a cached value; validate it 2930 if ( 2931 ( $wrapped[self::FLD_FORMAT_VERSION] ?? null ) === self::VERSION && 2932 $wrapped[self::FLD_TIME] >= $this->epoch 2933 ) { 2934 if ( $wrapped[self::FLD_TTL] > 0 ) { 2935 // Get the approximate time left on the key 2936 $age = $now - $wrapped[self::FLD_TIME]; 2937 $curTTL = max( $wrapped[self::FLD_TTL] - $age, 0.0 ); 2938 } else { 2939 // Key had no TTL, so the time left is unbounded 2940 $curTTL = INF; 2941 } 2942 $value = $wrapped[self::FLD_VALUE]; 2943 $info[self::KEY_VERSION] = $wrapped[self::FLD_VALUE_VERSION] ?? null; 2944 $info[self::KEY_AS_OF] = $wrapped[self::FLD_TIME]; 2945 $info[self::KEY_CUR_TTL] = $curTTL; 2946 $info[self::KEY_TTL] = $wrapped[self::FLD_TTL]; 2947 } 2948 } else { 2949 // Entry expected to be a tombstone; parse it 2950 $purge = $this->parsePurgeValue( $wrapped ); 2951 if ( $purge !== false ) { 2952 // Tombstoned keys should always have a negative current $ttl 2953 $info[self::KEY_CUR_TTL] = 2954 min( $purge[self::PURGE_TIME] - $now, self::TINY_NEGATIVE ); 2955 $info[self::KEY_TOMB_AS_OF] = $purge[self::PURGE_TIME]; 2956 } 2957 } 2958 2959 return [ $value, $info ]; 2960 } 2961 2962 /** 2963 * @return null[] 2964 */ 2965 private function newKeyInfoPlaceholder() { 2966 return [ 2967 self::KEY_VERSION => null, 2968 self::KEY_AS_OF => null, 2969 self::KEY_TTL => null, 2970 self::KEY_CUR_TTL => null, 2971 self::KEY_TOMB_AS_OF => null 2972 ]; 2973 } 2974 2975 /** 2976 * @param string $key String of the format <scope>:<collection>[:<constant or variable>]... 2977 * @return string A collection name to describe this class of key 2978 */ 2979 private function determineKeyClassForStats( $key ) { 2980 $parts = explode( ':', $key, 3 ); 2981 // Sanity fallback in case the key was not made by makeKey. 2982 // Replace dots because they are special in StatsD (T232907) 2983 return strtr( $parts[1] ?? $parts[0], '.', '_' ); 2984 } 2985 2986 /** 2987 * Extract purge metadata from cached value if it is a valid purge value 2988 * 2989 * Valid purge values come from makeTombstonePurgeValue()/makeCheckKeyPurgeValue() 2990 * 2991 * @param mixed $value Cached value 2992 * @return array|bool Array containing a UNIX timestamp (float) and hold-off period (integer), 2993 * or false if value isn't a valid purge value 2994 */ 2995 private function parsePurgeValue( $value ) { 2996 if ( !is_string( $value ) ) { 2997 return false; 2998 } 2999 3000 $segments = explode( ':', $value, 3 ); 3001 if ( isset( $segments[2] ) ) { 3002 $prefix = $segments[0]; 3003 $timestamp = (float)$segments[1]; 3004 $holdoff = (int)$segments[2]; 3005 } elseif ( isset( $segments[1] ) ) { 3006 $prefix = $segments[0]; 3007 $timestamp = (float)$segments[1]; 3008 // Value tombstones don't store hold-off TTLs 3009 $holdoff = self::HOLDOFF_TTL; 3010 } else { 3011 return false; 3012 } 3013 3014 if ( "{$prefix}:" !== self::PURGE_VAL_PREFIX || $timestamp < $this->epoch ) { 3015 // Not a purge value or the purge value is too old 3016 return false; 3017 } 3018 3019 return [ self::PURGE_TIME => $timestamp, self::PURGE_HOLDOFF => $holdoff ]; 3020 } 3021 3022 /** 3023 * @param float $timestamp UNIX timestamp 3024 * @return string Wrapped purge value; format is "PURGED:<timestamp>" 3025 */ 3026 private function makeTombstonePurgeValue( $timestamp ) { 3027 return self::PURGE_VAL_PREFIX . number_format( $timestamp, 4, '.', '' ); 3028 } 3029 3030 /** 3031 * @param float $timestamp UNIX timestamp 3032 * @param int $holdoff In seconds 3033 * @return string Wrapped purge value; format is "PURGED:<timestamp>:<holdoff>" 3034 */ 3035 private function makeCheckPurgeValue( $timestamp, int $holdoff ) { 3036 return self::PURGE_VAL_PREFIX . number_format( $timestamp, 4, '.', '' ) . ":$holdoff"; 3037 } 3038 3039 /** 3040 * @param string $group 3041 * @return MapCacheLRU 3042 */ 3043 private function getProcessCache( $group ) { 3044 if ( !isset( $this->processCaches[$group] ) ) { 3045 list( , $size ) = explode( ':', $group ); 3046 $this->processCaches[$group] = new MapCacheLRU( (int)$size ); 3047 if ( $this->wallClockOverride !== null ) { 3048 $this->processCaches[$group]->setMockTime( $this->wallClockOverride ); 3049 } 3050 } 3051 3052 return $this->processCaches[$group]; 3053 } 3054 3055 /** 3056 * @param string $key Cache key made with makeKey()/makeGlobalKey() 3057 * @param int $version 3058 * @return string 3059 */ 3060 private function getProcessCacheKey( $key, $version ) { 3061 return $key . ' ' . (int)$version; 3062 } 3063 3064 /** 3065 * @param ArrayIterator $keys 3066 * @param array $opts 3067 * @return string[] Map of (ID => cache key) 3068 */ 3069 private function getNonProcessCachedMultiKeys( ArrayIterator $keys, array $opts ) { 3070 $pcTTL = $opts['pcTTL'] ?? self::TTL_UNCACHEABLE; 3071 3072 $keysMissing = []; 3073 if ( $pcTTL > 0 && $this->callbackDepth == 0 ) { 3074 $version = $opts['version'] ?? null; 3075 $pCache = $this->getProcessCache( $opts['pcGroup'] ?? self::PC_PRIMARY ); 3076 foreach ( $keys as $key => $id ) { 3077 if ( !$pCache->has( $this->getProcessCacheKey( $key, $version ), $pcTTL ) ) { 3078 $keysMissing[$id] = $key; 3079 } 3080 } 3081 } 3082 3083 return $keysMissing; 3084 } 3085 3086 /** 3087 * @param string[] $keys Cache keys made with makeKey()/makeGlobalKey() 3088 * @param string[]|string[][] $checkKeys Map of (integer or cache key => "check" key(s)); 3089 * "check" keys must also be made with makeKey()/makeGlobalKey() 3090 * @return array<string,mixed> Map of (sister key => value, or, false if not found) 3091 */ 3092 private function fetchWrappedValuesForWarmupCache( array $keys, array $checkKeys ) { 3093 if ( !$keys ) { 3094 return []; 3095 } 3096 3097 // Get all the value keys to fetch... 3098 $sisterKeys = $this->makeSisterKeys( $keys, self::TYPE_VALUE, $this->onHostRoute ); 3099 // Get all the flux keys to fetch... 3100 if ( $this->onHostRoute !== null ) { 3101 foreach ( $keys as $key ) { 3102 $sisterKeys[] = $this->makeSisterKey( $key, self::TYPE_FLUX ); 3103 } 3104 } 3105 // Get all the "check" keys to fetch... 3106 foreach ( $checkKeys as $i => $checkKeyOrKeyGroup ) { 3107 // Note: avoid array_merge() inside loop in case there are many keys 3108 if ( is_int( $i ) ) { 3109 // Single "check" key that applies to all value keys 3110 $sisterKeys[] = $this->makeSisterKey( $checkKeyOrKeyGroup, self::TYPE_TIMESTAMP ); 3111 } else { 3112 // List of "check" keys that apply to a specific value key 3113 foreach ( (array)$checkKeyOrKeyGroup as $checkKey ) { 3114 $sisterKeys[] = $this->makeSisterKey( $checkKey, self::TYPE_TIMESTAMP ); 3115 } 3116 } 3117 } 3118 3119 $wrappedBySisterKey = $this->cache->getMulti( $sisterKeys ); 3120 $wrappedBySisterKey += array_fill_keys( $sisterKeys, false ); 3121 3122 return $wrappedBySisterKey; 3123 } 3124 3125 /** 3126 * @return float UNIX timestamp 3127 * @codeCoverageIgnore 3128 */ 3129 protected function getCurrentTime() { 3130 if ( $this->wallClockOverride ) { 3131 return $this->wallClockOverride; 3132 } 3133 3134 $clockTime = (float)time(); // call this first 3135 // microtime() uses an initial gettimeofday() call added to usage clocks. 3136 // This can severely drift from time() and the microtime() value of other threads 3137 // due to undercounting of the amount of time elapsed. Instead of seeing the current 3138 // time as being in the past, use the value of time(). This avoids setting cache values 3139 // that will immediately be seen as expired and possibly cause stampedes. 3140 return max( microtime( true ), $clockTime ); 3141 } 3142 3143 /** 3144 * @param float|null &$time Mock UNIX timestamp for testing 3145 * @codeCoverageIgnore 3146 */ 3147 public function setMockTime( &$time ) { 3148 $this->wallClockOverride =& $time; 3149 $this->cache->setMockTime( $time ); 3150 foreach ( $this->processCaches as $pCache ) { 3151 $pCache->setMockTime( $time ); 3152 } 3153 } 3154} 3155