objectcache: Make WANObjectCache interim caching not interfere with ChronologyProtector

[lhc/web/wiklou.git] / includes / libs / objectcache / WANObjectCache.php

diff --git a/includes/libs/objectcache/WANObjectCache.php b/includes/libs/objectcache/WANObjectCache.php
index db27e42..74ec7b9 100644 (file)
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -91,6 +91,8 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
        protected $logger;
        /** @var StatsdDataFactoryInterface */
        protected $stats;
+       /** @var bool Whether to use "interim" caching while keys are tombstoned */
+       protected $useInterimHoldOffCaching = true;
 
        /** @var int ERR_* constant for the "last error" registry */
        protected $lastRelayError = self::ERR_NONE;
@@ -1104,6 +1106,10 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
         * @return mixed
         */
        protected function getInterimValue( $key, $versioned, $minTime, &$asOf ) {
+               if ( !$this->useInterimHoldOffCaching ) {
+                       return false; // disabled
+               }
+
                $wrapped = $this->cache->get( self::INTERIM_KEY_PREFIX . $key );
                list( $value ) = $this->unwrap( $wrapped, $this->getCurrentTime() );
                if ( $value !== false && $this->isValid( $value, $versioned, $asOf, $minTime ) ) {
@@ -1495,6 +1501,30 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
                $this->processCaches = [];
        }
 
+       /**
+        * Disable the use of brief caching for tombstoned keys
+        *
+        * When a key is purged via delete(), there normally is a period where caching
+        * is hold-off limited to an extremely short time. This method will disable that
+        * caching, forcing the callback to run for any of:
+        *   - WANObjectCache::getWithSetCallback()
+        *   - WANObjectCache::getMultiWithSetCallback()
+        *   - WANObjectCache::getMultiWithUnionSetCallback()
+        *
+        * This is useful when both:
+        *   - a) the database used by the callback is known to be up-to-date enough
+        *        for some particular purpose (e.g. replica DB has applied transaction X)
+        *   - b) the caller needs to exploit that fact, and therefore needs to avoid the
+        *        use of inherently volatile and possibly stale interim keys
+        *
+        * @see WANObjectCache::delete()
+        * @param bool $enabled Whether to enable interim caching
+        * @since 1.31
+        */
+       public function useInterimHoldOffCaching( $enabled ) {
+               $this->useInterimHoldOffCaching = $enabled;
+       }
+
        /**
         * @param int $flag ATTR_* class constant
         * @return int QOS_* class constant