* Multi-datacenter aware caching interface
*
* All operations go to the local datacenter cache, except for delete(),
- * touchCheckKey(), and resetCheckKey(), which broadcast to all clusters.
+ * touchCheckKey(), and resetCheckKey(), which broadcast to all datacenters.
*
* This class is intended for caching data from primary stores.
* If the get() method does not return a value, then the caller
* that subscribe to the endpoint and update the caches.
*
* Broadcasted operations like delete() and touchCheckKey() are done
- * synchronously in the local cluster, but are relayed asynchronously.
+ * synchronously in the local datacenter, but are relayed asynchronously.
* This means that callers in other datacenters will see older values
- * for a however many milliseconds the datacenters are apart. As with
+ * for however many milliseconds the datacenters are apart. As with
* any cache, this should not be relied on for cases where reads are
* used to determine writes to source (e.g. non-cache) data stores.
*
* @since 1.26
*/
class WANObjectCache {
- /** @var BagOStuff The local cluster cache */
+ /** @var BagOStuff The local datacenter cache */
protected $cache;
/** @var string Cache pool name */
protected $pool;
* isolation can largely be maintained by doing the following:
* - a) Calling delete() on entity change *and* creation, before DB commit
* - b) Keeping transaction duration shorter than delete() hold-off TTL
- * However, pre-snapshot values might still be seen due to delete() relay lag.
+ * However, pre-snapshot values might still be seen if an update was made
+ * in a remote datacenter but the purge from delete() didn't relay yet.
*
* Consider using getWithSetCallback() instead of get()/set() cycles.
* That method has cache slam avoiding features for hot/expensive keys.
}
/**
- * Purge a key from all clusters
+ * Purge a key from all datacenters
*
* This should only be called when the underlying data (being cached)
* changes in a significant way. This deletes the key and starts a hold-off
$key = self::VALUE_KEY_PREFIX . $key;
// Avoid indefinite key salting for sanity
$ttl = max( $ttl, 1 );
- // Update the local cluster immediately
+ // Update the local datacenter immediately
$ok = $this->cache->set( $key, self::PURGE_VAL_PREFIX . microtime( true ), $ttl );
- // Publish the purge to all clusters
+ // Publish the purge to all datacenters
return $this->relayPurge( $key, $ttl ) && $ok;
}
}
/**
- * Purge a "check" key from all clusters, invalidating keys that use it
+ * Purge a "check" key from all datacenters, invalidating keys that use it
*
* This should only be called when the underlying data (being cached)
* changes in a significant way, and it is impractical to call delete()
*/
final public function touchCheckKey( $key ) {
$key = self::TIME_KEY_PREFIX . $key;
- // Update the local cluster immediately
+ // Update the local datacenter immediately
$ok = $this->cache->set( $key,
self::PURGE_VAL_PREFIX . microtime( true ), self::CHECK_KEY_TTL );
- // Publish the purge to all clusters
+ // Publish the purge to all datacenters
return $this->relayPurge( $key, self::CHECK_KEY_TTL ) && $ok;
}
/**
- * Delete a "check" key from all clusters, invalidating keys that use it
+ * Delete a "check" key from all datacenters, invalidating keys that use it
*
* This is similar to touchCheckKey() in that keys using it via
* getWithSetCallback() will be invalidated. The differences are:
*/
final public function resetCheckKey( $key ) {
$key = self::TIME_KEY_PREFIX . $key;
- // Update the local cluster immediately
+ // Update the local datacenter immediately
$ok = $this->cache->delete( $key );
- // Publish the purge to all clusters
+ // Publish the purge to all datacenters
return $this->relayDelete( $key ) && $ok;
}
* return $row;
* };
* // Get the key value from cache or from source on cache miss;
- * // try to only let one cluster thread manage doing cache updates
+ * // try to only let one datacenter thread manage doing cache updates
* $opts = array( 'lockTSE' => 5, 'lowTTL' => 10 );
* $value = $cache->getWithSetCallback( $key, $callback, 60, array(), $opts );
* @endcode
* // Function that derives the new key value
* $callback = function() { ... };
* // Get the key value from cache or from source on cache miss;
- * // try to only let one cluster thread manage doing cache updates
+ * // try to only let one datacenter thread manage doing cache updates
* $opts = array( 'lockTSE' => 5, 'lowTTL' => 10 );
* $value = $cache->getWithSetCallback( $key, $callback, 60, $checkKeys, $opts );
* @endcode
$lockAcquired = false;
if ( $useMutex ) {
- // Acquire a cluster-local non-blocking lock
+ // Acquire a datacenter-local non-blocking lock
if ( $this->cache->lock( $key, 0, self::LOCK_TTL ) ) {
// Lock acquired; this thread should update the key
$lockAcquired = true;
dépôts / lhc / web / wiklou.git / commitdiff