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objectcache: add another example case to WANObjectCache::getWithSetCallback()

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Change-Id: I4beb1441790f5371d9fe55ca05cd17dc9fcdcf80
This commit is contained in:
Aaron Schulz 2017-12-05 21:01:36 -08:00
parent 1801936f87
commit b62327eee7
1 changed files with 35 additions and 1 deletions
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36
includes/libs/objectcache/WANObjectCache.php
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@ -900,6 +900,40 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
* );
* @endcode
*
* Example usage (key holding an LRU subkey:value map; this can avoid flooding cache with
* keys for an unlimited set of (constraint,situation) pairs, thereby avoiding elevated
* cache evictions and wasted memory):
* @code
* $catSituationTolerabilityCache = $this->cache->getWithSetCallback(
* // Group by constraint ID/hash, cat family ID/hash, or something else useful
* $this->cache->makeKey( 'cat-situation-tolerablity-checks', $groupKey ),
* WANObjectCache::TTL_DAY, // rarely used groups should fade away
* // The $scenarioKey format is $constraintId:<ID/hash of $situation>
* function ( $cacheMap ) use ( $scenarioKey, $constraintId, $situation ) {
* $lruCache = MapCacheLRU::newFromArray( $cacheMap ?: [], self::CACHE_SIZE );
* $result = $lruCache->get( $scenarioKey ); // triggers LRU bump if present
* if ( $result === null || $this->isScenarioResultExpired( $result ) ) {
* $result = $this->checkScenarioTolerability( $constraintId, $situation );
* $lruCache->set( $scenarioKey, $result, 3 / 8 );
* }
* // Save the new LRU cache map and reset the map's TTL
* return $lruCache->toArray();
* },
* [
* // Once map is > 1 sec old, consider refreshing
* 'ageNew' => 1,
* // Update within 5 seconds after "ageNew" given a 1hz cache check rate
* 'hotTTR' => 5,
* // Avoid querying cache servers multiple times in a request; this also means
* // that a request can only alter the value of any given constraint key once
* 'pcTTL' => WANObjectCache::TTL_PROC_LONG
* ]
* );
* $tolerability = isset( $catSituationTolerabilityCache[$scenarioKey] )
* ? $catSituationTolerabilityCache[$scenarioKey]
* : $this->checkScenarioTolerability( $constraintId, $situation );
* @endcode
*
* @see WANObjectCache::get()
* @see WANObjectCache::set()
*
@ -1678,7 +1712,7 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
* $ttl = ( $newList === $oldValue )
* // No change: cache for 150% of the age of $oldValue
* ? $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, 1.5 )
* // Changed: cache for %50 of the age of $oldValue
* // Changed: cache for 50% of the age of $oldValue
* : $cache->adaptiveTTL( $oldAsOf, $maxTTL, $minTTL, .5 );
* }
*