jenkins-bot has submitted this change and it was merged. (
https://gerrit.wikimedia.org/r/394525 )
Change subject: objectcache: add example use case to
WANObjectCache::getMultiCheckKeyTime()
......................................................................
objectcache: add example use case to WANObjectCache::getMultiCheckKeyTime()
Change-Id: I874070d2f770be7f9e06c381b2413f6e133418b8
---
M includes/libs/objectcache/WANObjectCache.php
1 file changed, 50 insertions(+), 1 deletion(-)
Approvals:
Krinkle: Looks good to me, approved
jenkins-bot: Verified
diff --git a/includes/libs/objectcache/WANObjectCache.php
b/includes/libs/objectcache/WANObjectCache.php
index 68da16d..ddf5d35 100644
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -611,9 +611,58 @@
* Fetch the values of each timestamp "check" key
*
* This works like getCheckKeyTime() except it takes a list of keys
- * and returns a list of timestamps instead of just that of one key
+ * and returns a map of timestamps instead of just that of one key
+ *
+ * This might be useful if both:
+ * - a) a class of entities each depend on hundreds of other entities
+ * - b) these other entities are depended upon by millions of entities
+ *
+ * The later entities can each use a "check" key to invalidate their
dependee entities.
+ * However, it is expensive for the former entities to verify against
all of the relevant
+ * "check" keys during each getWithSetCallback() call. A less expensive
approach is to do
+ * these verifications only after a "time-till-verify" (TTV) has
passed. This is a middle
+ * ground between using blind TTLs and using constant verification. The
adaptiveTTL() method
+ * can be used to dynamically adjust the TTV. Also, the initial TTV can
make use of the
+ * last-modified times of the dependant entities (either from the DB or
the "check" keys).
+ *
+ * Example usage:
+ * @code
+ * $value = $cache->getWithSetCallback(
+ * $cache->makeGlobalKey( 'wikibase-item', $id ),
+ * self::INITIAL_TTV, // initial time-till-verify
+ * function ( $oldValue, &$ttv, &$setOpts, $oldAsOf ) use (
$checkKeys, $cache ) {
+ * $now = microtime( true );
+ * // Use $oldValue if it passes max ultimate age and
"check" key comparisons
+ * if ( $oldValue &&
+ * $oldAsOf > max( $cache->getMultiCheckKeyTime(
$checkKeys ) ) &&
+ * ( $now - $oldValue['ctime'] ) <= self::MAX_CACHE_AGE
+ * ) {
+ * // Increase time-till-verify by 50% of last time to
reduce overhead
+ * $ttv = $cache->adaptiveTTL( $oldAsOf, self::MAX_TTV,
self::MIN_TTV, 1.5 );
+ * // Unlike $oldAsOf, "ctime" is the ultimate age of
the cached data
+ * return $oldValue;
+ * }
+ *
+ * $mtimes = []; // dependency last-modified times; passed
by reference
+ * $value = [ 'data' => $this->fetchEntityData( $mtimes ),
'ctime' => $now ];
+ * // Guess time-till-change among the dependencies, e.g.
1/(total change rate)
+ * $ttc = 1 / array_sum( array_map(
+ * function ( $mtime ) use ( $now ) {
+ * return 1 / ( $mtime ? ( $now - $mtime ) : 900 );
+ * },
+ * $mtimes
+ * ) );
+ * // The time-to-verify should not be overly pessimistic
nor optimistic
+ * $ttv = min( max( $ttc, self::MIN_TTV ), self::MAX_TTV );
+ *
+ * return $value;
+ * },
+ * [ 'staleTTL' => $cache::TTL_DAY ] // keep around to verify
and re-save
+ * );
+ * @endcode
*
* @see WANObjectCache::getCheckKeyTime()
+ * @see WANObjectCache::getWithSetCallback()
*
* @param array $keys
* @return float[] Map of (key => UNIX timestamp)
--
To view, visit https://gerrit.wikimedia.org/r/394525
To unsubscribe, visit https://gerrit.wikimedia.org/r/settings
Gerrit-MessageType: merged
Gerrit-Change-Id: I874070d2f770be7f9e06c381b2413f6e133418b8
Gerrit-PatchSet: 4
Gerrit-Project: mediawiki/core
Gerrit-Branch: master
Gerrit-Owner: Aaron Schulz <[email protected]>
Gerrit-Reviewer: Krinkle <[email protected]>
Gerrit-Reviewer: jenkins-bot <>
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