<?php
/**
- *
- * @package MediaWiki
+ *
*
* DB accessable external objects
*
*/
-require_once( 'LoadBalancer.php' );
-/** @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
- */
+ /** @todo Document.*/
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];
+ $wgExternalLoadBalancers[$cluster]->allowLagged(true);
+ return $wgExternalLoadBalancers[$cluster];
}
-
+
+ /** @todo Document.*/
function &getSlave( $cluster ) {
$lb =& $this->getLoadBalancer( $cluster );
return $lb->getConnection( DB_SLAVE );
}
+ /** @todo Document.*/
function &getMaster( $cluster ) {
$lb =& $this->getLoadBalancer( $cluster );
return $lb->getConnection( DB_MASTER );
- }
-
+ }
+
+ /** @todo Document.*/
+ function getTable( &$db ) {
+ $table = $db->getLBInfo( 'blobs table' );
+ if ( is_null( $table ) ) {
+ $table = 'blobs';
+ }
+ return $table;
+ }
+
+ /**
+ * Fetch data from given URL
+ * @param string $url An url of the form DB://cluster/id or DB://cluster/id/itemid for concatened storage.
+ */
function fetchFromURL($url) {
- global $wgExternalServers;
- #
- # URLs have the form DB://cluster/id or DB://cluster/id/itemid for concatenated storage
- #
$path = explode( '/', $url );
$cluster = $path[2];
$id = $path[3];
$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 );
+ if ( $itemID !== false && $ret !== false ) {
+ 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.
+ * @param $cluster
+ * @param $id
+ * @param $itemID
+ * @return mixed
+ * @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( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ) );
+ if ( $ret === false ) {
+ wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" );
+ // Try the master
+ $dbw =& $this->getMaster( $cluster );
+ $ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ) );
+ if( $ret === false) {
+ wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" );
+ }
+ }
+ if( $itemID !== false && $ret !== false ) {
+ // Unserialise object; caller extracts item
+ $ret = unserialize( $ret );
+ }
+
+ $wgExternalBlobCache = array( $cacheID => &$ret );
+ return $ret;
+ }
+
/**
* Insert a data item into a given cluster
*
- * @param string $cluster The cluster name
- * @param string $data The data item
+ * @param $cluster String: the cluster name
+ * @param $data String: the data item
* @return string URL
*/
function store( $cluster, $data ) {
- global $wgExternalServers;
$fname = 'ExternalStoreDB::store';
$dbw =& $this->getMaster( $cluster );
$id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
- $dbw->insert( 'blobs', array( 'blob_id' => $id, 'blob_text' => $data ), $fname );
- return "DB://$cluster/" . $dbw->insertId();
+ $dbw->insert( $this->getTable( $dbw ), array( 'blob_id' => $id, 'blob_text' => $data ), $fname );
+ $id = $dbw->insertId();
+ if ( $dbw->getFlag( DBO_TRX ) ) {
+ $dbw->immediateCommit();
+ }
+ return "DB://$cluster/$id";
}
}
-?>
+
dépôts / lhc / web / wiklou.git / blobdiff