/** @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 {
/**
* Fetch data from given URL
* @param string $url An url
*/
+
+ function &getLoadBalancer( $cluster ) {
+ global $wgExternalServers, $wgExternalLoadBalancers;
+ if ( !array_key_exists( $cluster, $wgExternalLoadBalancers ) ) {
+ $wgExternalLoadBalancers[$cluster] = LoadBalancer::newFromParams( $wgExternalServers[$cluster] );
+ }
+ return $wgExternalLoadBalancers[$cluster];
+ }
+
+ function &getSlave( $cluster ) {
+ $lb =& $this->getLoadBalancer( $cluster );
+ return $lb->getConnection( DB_SLAVE );
+ }
+
+ function &getMaster( $cluster ) {
+ $lb =& $this->getLoadBalancer( $cluster );
+ return $lb->getConnection( DB_MASTER );
+ }
+
+ function getTable( &$db ) {
+ $table = $db->getLBInfo( 'blobs table' );
+ if ( is_null( $table ) ) {
+ $table = 'blobs';
+ }
+ return $table;
+ }
+
function fetchFromURL($url) {
global $wgExternalServers;
#
- # URLs have the form DB://cluster/id, e.g.
- # DB://cluster1/3298247
+ # URLs have the form DB://cluster/id or DB://cluster/id/itemid for concatenated storage
#
$path = explode( '/', $url );
$cluster = $path[2];
$id = $path[3];
+ if ( isset( $path[4] ) ) {
+ $itemID = $path[4];
+ } else {
+ $itemID = false;
+ }
- $lb = LoadBalancer::NewFromParams( $wgExternalServers[$cluster] );
- $db = $lb->getConnection( DB_SLAVE );
+ $ret =& $this->fetchBlob( $cluster, $id, $itemID );
- $ret = $db->selectField( 'blobs', 'blob_text', array( 'blob_id' => $id ) );
+ if ( $itemID !== 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.
+ * @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( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ) );
+ if( $itemID !== false ) {
+ // Unserialise object; caller extracts item
+ $ret = unserialize( $ret );
+ }
+
+ $wgExternalBlobCache = array( $cacheID => &$ret );
return $ret;
}
- /* @fixme XXX: may require other methods, for store, delete,
- * whatever, for initial ext storage
+ /**
+ * Insert a data item into a given cluster
+ *
+ * @param string $cluster The cluster name
+ * @param string $data 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( $this->getTable( $dbw ), array( 'blob_id' => $id, 'blob_text' => $data ), $fname );
+ return "DB://$cluster/" . $dbw->insertId();
+ }
}
?>