/** @package MediaWiki */
+/**
+ * External database storage will use one (or more) separate connection pools
+ * from what the main wiki uses. If we load many revisions, such as when doing
+ * bulk backups or maintenance, we want to keep them around over the lifetime
+ * of the script.
+ *
+ * Associative array of LoadBalancer objects, indexed by cluster name.
+ */
+global $wgExternalLoadBalancers;
+$wgExternalLoadBalancers = array();
+
+/**
+ * One-step cache variable to hold base blobs; operations that
+ * pull multiple revisions may often pull multiple times from
+ * the same blob. By keeping the last-used one open, we avoid
+ * redundant unserialization and decompression overhead.
+ */
+global $wgExternalBlobCache;
+$wgExternalBlobCache = array();
+
class ExternalStoreDB {
- var $loadBalancers = array();
-
/**
* Fetch data from given URL
* @param string $url An url
*/
function &getLoadBalancer( $cluster ) {
- global $wgExternalServers;
- if ( !array_key_exists( $cluster, $this->loadBalancers ) ) {
- $this->loadBalancers[$cluster] = LoadBalancer::newFromParams( $wgExternalServers[$cluster] );
+ global $wgExternalServers, $wgExternalLoadBalancers;
+ if ( !array_key_exists( $cluster, $wgExternalLoadBalancers ) ) {
+ $wgExternalLoadBalancers[$cluster] = LoadBalancer::newFromParams( $wgExternalServers[$cluster] );
}
- return $this->loadBalancers[$cluster];
+ return $wgExternalLoadBalancers[$cluster];
}
function &getSlave( $cluster ) {
$itemID = false;
}
- $dbr =& $this->getSlave( $cluster );
- $ret = $dbr->selectField( 'blobs', 'blob_text', array( 'blob_id' => $id ) );
+ $ret =& $this->fetchBlob( $cluster, $id, $itemID );
if ( $itemID !== false ) {
- # Unserialise object and get item
- $obj = unserialize( $ret );
- $ret = $obj->getItem( $itemID );
+ return $ret->getItem( $itemID );
+ }
+ return $ret;
+ }
+
+ /**
+ * Fetch a blob item out of the database; a cache of the last-loaded
+ * blob will be kept so that multiple loads out of a multi-item blob
+ * can avoid redundant database access and decompression.
+ * @return mixed
+ * @access private
+ */
+ function &fetchBlob( $cluster, $id, $itemID ) {
+ global $wgExternalBlobCache;
+ $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
+ if( isset( $wgExternalBlobCache[$cacheID] ) ) {
+ wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
+ return $wgExternalBlobCache[$cacheID];
+ }
+
+ wfDebug( "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
+
+ $dbr =& $this->getSlave( $cluster );
+ $ret = $dbr->selectField( 'blobs', 'blob_text', array( 'blob_id' => $id ) );
+ if( $itemID !== false ) {
+ // Unserialise object; caller extracts item
+ $ret = unserialize( $ret );
}
+
+ $wgExternalBlobCache = array( $cacheID => &$ret );
return $ret;
}