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<?php
/**
* External storage in SQL database.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
* http://www.gnu.org/copyleft/gpl.html
*
* @file
*/
/**
* DB accessable external objects.
*
* In this system, each store "location" maps to a database "cluster".
* The clusters must be defined in the normal LBFactory configuration.
*
* @ingroup ExternalStorage
*/
class ExternalStoreDB extends ExternalStoreMedium {
/**
* The URL returned is of the form of the form DB://cluster/id
* or DB://cluster/id/itemid for concatened storage.
*
* @see ExternalStoreMedium::fetchFromURL()
*/
public function fetchFromURL( $url ) {
$path = explode( '/', $url );
$cluster = $path[2];
$id = $path[3];
if ( isset( $path[4] ) ) {
$itemID = $path[4];
} else {
$itemID = false;
}
$ret =& $this->fetchBlob( $cluster, $id, $itemID );
if ( $itemID !== false && $ret !== false ) {
return $ret->getItem( $itemID );
}
return $ret;
}
/**
* @see ExternalStoreMedium::store()
*/
public function store( $cluster, $data ) {
$dbw = $this->getMaster( $cluster );
$id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
$dbw->insert( $this->getTable( $dbw ),
array( 'blob_id' => $id, 'blob_text' => $data ),
__METHOD__ );
$id = $dbw->insertId();
if ( !$id ) {
throw new MWException( __METHOD__.': no insert ID' );
}
if ( $dbw->getFlag( DBO_TRX ) ) {
$dbw->commit( __METHOD__ );
}
return "DB://$cluster/$id";
}
/**
* Get a LoadBalancer for the specified cluster
*
* @param string $cluster cluster name
* @return LoadBalancer object
*/
function &getLoadBalancer( $cluster ) {
$wiki = isset( $this->params['wiki'] ) ? $this->params['wiki'] : false;
return wfGetLBFactory()->getExternalLB( $cluster, $wiki );
}
/**
* Get a slave database connection for the specified cluster
*
* @param string $cluster cluster name
* @return DatabaseBase object
*/
function &getSlave( $cluster ) {
global $wgDefaultExternalStore;
$wiki = isset( $this->params['wiki'] ) ? $this->params['wiki'] : false;
$lb =& $this->getLoadBalancer( $cluster );
if ( !in_array( "DB://" . $cluster, (array)$wgDefaultExternalStore ) ) {
wfDebug( "read only external store" );
$lb->allowLagged( true );
} else {
wfDebug( "writable external store" );
}
return $lb->getConnection( DB_SLAVE, array(), $wiki );
}
/**
* Get a master database connection for the specified cluster
*
* @param string $cluster cluster name
* @return DatabaseBase object
*/
function &getMaster( $cluster ) {
$wiki = isset( $this->params['wiki'] ) ? $this->params['wiki'] : false;
$lb =& $this->getLoadBalancer( $cluster );
return $lb->getConnection( DB_MASTER, array(), $wiki );
}
/**
* Get the 'blobs' table name for this database
*
* @param $db DatabaseBase
* @return String: table name ('blobs' by default)
*/
function getTable( &$db ) {
$table = $db->getLBInfo( 'blobs table' );
if ( is_null( $table ) ) {
$table = 'blobs';
}
return $table;
}
/**
* 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 ) {
/**
* 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.
*/
static $externalBlobCache = array();
$cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
if( isset( $externalBlobCache[$cacheID] ) ) {
wfDebugLog( 'ExternalStoreDB-cache', "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
return $externalBlobCache[$cacheID];
}
wfDebugLog( 'ExternalStoreDB-cache', "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
$dbr =& $this->getSlave( $cluster );
$ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
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 ), __METHOD__ );
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 );
}
$externalBlobCache = array( $cacheID => &$ret );
return $ret;
}
}
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