Current File : /www/varak.net/wiki.varak.net/includes/externalstore/ExternalStoreDB.php
<?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
*/
use MediaWiki\MediaWikiServices;
use Wikimedia\Rdbms\ILoadBalancer;
use Wikimedia\Rdbms\IDatabase;
use Wikimedia\Rdbms\DBConnRef;
use Wikimedia\Rdbms\MaintainableDBConnRef;
use Wikimedia\Rdbms\DatabaseDomain;
/**
* DB accessible 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 provided URL is in the form of DB://cluster/id
* or DB://cluster/id/itemid for concatened storage.
*
* @param string $url
* @return string|bool False if missing
* @see ExternalStoreMedium::fetchFromURL()
*/
public function fetchFromURL( $url ) {
list( $cluster, $id, $itemID ) = $this->parseURL( $url );
$ret = $this->fetchBlob( $cluster, $id, $itemID );
if ( $itemID !== false && $ret !== false ) {
return $ret->getItem( $itemID );
}
return $ret;
}
/**
* Fetch data from given external store URLs.
* The provided URLs are in the form of DB://cluster/id
* or DB://cluster/id/itemid for concatened storage.
*
* @param array $urls An array of external store URLs
* @return array A map from url to stored content. Failed results
* are not represented.
*/
public function batchFetchFromURLs( array $urls ) {
$batched = $inverseUrlMap = [];
foreach ( $urls as $url ) {
list( $cluster, $id, $itemID ) = $this->parseURL( $url );
$batched[$cluster][$id][] = $itemID;
// false $itemID gets cast to int, but should be ok
// since we do === from the $itemID in $batched
$inverseUrlMap[$cluster][$id][$itemID] = $url;
}
$ret = [];
foreach ( $batched as $cluster => $batchByCluster ) {
$res = $this->batchFetchBlobs( $cluster, $batchByCluster );
/** @var HistoryBlob $blob */
foreach ( $res as $id => $blob ) {
foreach ( $batchByCluster[$id] as $itemID ) {
$url = $inverseUrlMap[$cluster][$id][$itemID];
if ( $itemID === false ) {
$ret[$url] = $blob;
} else {
$ret[$url] = $blob->getItem( $itemID );
}
}
}
}
return $ret;
}
public function store( $location, $data ) {
$dbw = $this->getMaster( $location );
$dbw->insert( $this->getTable( $dbw ),
[ 'blob_text' => $data ],
__METHOD__ );
$id = $dbw->insertId();
if ( !$id ) {
throw new MWException( __METHOD__ . ': no insert ID' );
}
return "DB://$location/$id";
}
public function isReadOnly( $location ) {
return ( $this->getLoadBalancer( $location )->getReadOnlyReason() !== false );
}
/**
* Get a LoadBalancer for the specified cluster
*
* @param string $cluster Cluster name
* @return ILoadBalancer
*/
private function getLoadBalancer( $cluster ) {
$lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
return $lbFactory->getExternalLB( $cluster );
}
/**
* Get a replica DB connection for the specified cluster
*
* @param string $cluster Cluster name
* @return DBConnRef
*/
public function getSlave( $cluster ) {
global $wgDefaultExternalStore;
$lb = $this->getLoadBalancer( $cluster );
$domainId = $this->getDomainId( $lb->getServerInfo( $lb->getWriterIndex() ) );
if ( !in_array( "DB://" . $cluster, (array)$wgDefaultExternalStore ) ) {
wfDebug( "read only external store\n" );
$lb->allowLagged( true );
} else {
wfDebug( "writable external store\n" );
}
$db = $lb->getConnectionRef( DB_REPLICA, [], $domainId );
$db->clearFlag( DBO_TRX ); // sanity
return $db;
}
/**
* Get a master database connection for the specified cluster
*
* @param string $cluster Cluster name
* @return MaintainableDBConnRef
*/
public function getMaster( $cluster ) {
$lb = $this->getLoadBalancer( $cluster );
$domainId = $this->getDomainId( $lb->getServerInfo( $lb->getWriterIndex() ) );
$db = $lb->getMaintenanceConnectionRef( DB_MASTER, [], $domainId );
$db->clearFlag( DBO_TRX ); // sanity
return $db;
}
/**
* @param array $server Master DB server configuration array for LoadBalancer
* @return string|bool Database domain ID or false
*/
private function getDomainId( array $server ) {
if ( isset( $this->params['wiki'] ) ) {
return $this->params['wiki']; // explicit domain
}
if ( isset( $server['dbname'] ) ) {
// T200471: for b/c, treat any "dbname" field as forcing which database to use.
// MediaWiki/LoadBalancer previously did not enforce any concept of a local DB
// domain, but rather assumed that the LB server configuration matched $wgDBname.
// This check is useful when the external storage DB for this cluster does not use
// the same name as the corresponding "main" DB(s) for wikis.
$domain = new DatabaseDomain(
$server['dbname'],
$server['schema'] ?? null,
$server['tablePrefix'] ?? ''
);
return $domain->getId();
}
return false; // local LB domain
}
/**
* Get the 'blobs' table name for this database
*
* @param IDatabase $db
* @return string Table name ('blobs' by default)
*/
public 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 string $cluster
* @param string $id
* @param string $itemID
* @return HistoryBlob|bool Returns false if missing
*/
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 = [];
$cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
$wiki = $this->params['wiki'] ?? false;
$cacheID = ( $wiki === false ) ? $cacheID : "$cacheID@$wiki";
if ( isset( $externalBlobCache[$cacheID] ) ) {
wfDebugLog( 'ExternalStoreDB-cache',
"ExternalStoreDB::fetchBlob cache hit on $cacheID" );
return $externalBlobCache[$cacheID];
}
wfDebugLog( 'ExternalStoreDB-cache',
"ExternalStoreDB::fetchBlob cache miss on $cacheID" );
$dbr = $this->getSlave( $cluster );
$ret = $dbr->selectField( $this->getTable( $dbr ),
'blob_text', [ 'blob_id' => $id ], __METHOD__ );
if ( $ret === false ) {
wfDebugLog( 'ExternalStoreDB',
"ExternalStoreDB::fetchBlob master fallback on $cacheID" );
// Try the master
$dbw = $this->getMaster( $cluster );
$ret = $dbw->selectField( $this->getTable( $dbw ),
'blob_text', [ 'blob_id' => $id ], __METHOD__ );
if ( $ret === false ) {
wfDebugLog( 'ExternalStoreDB',
"ExternalStoreDB::fetchBlob master failed to find $cacheID" );
}
}
if ( $itemID !== false && $ret !== false ) {
// Unserialise object; caller extracts item
$ret = unserialize( $ret );
}
$externalBlobCache = [ $cacheID => $ret ];
return $ret;
}
/**
* Fetch multiple blob items out of the database
*
* @param string $cluster A cluster name valid for use with LBFactory
* @param array $ids A map from the blob_id's to look for to the requested itemIDs in the blobs
* @return array A map from the blob_id's requested to their content.
* Unlocated ids are not represented
*/
private function batchFetchBlobs( $cluster, array $ids ) {
$dbr = $this->getSlave( $cluster );
$res = $dbr->select( $this->getTable( $dbr ),
[ 'blob_id', 'blob_text' ], [ 'blob_id' => array_keys( $ids ) ], __METHOD__ );
$ret = [];
if ( $res !== false ) {
$this->mergeBatchResult( $ret, $ids, $res );
}
if ( $ids ) {
wfDebugLog( __CLASS__, __METHOD__ .
" master fallback on '$cluster' for: " .
implode( ',', array_keys( $ids ) ) );
// Try the master
$dbw = $this->getMaster( $cluster );
$res = $dbw->select( $this->getTable( $dbr ),
[ 'blob_id', 'blob_text' ],
[ 'blob_id' => array_keys( $ids ) ],
__METHOD__ );
if ( $res === false ) {
wfDebugLog( __CLASS__, __METHOD__ . " master failed on '$cluster'" );
} else {
$this->mergeBatchResult( $ret, $ids, $res );
}
}
if ( $ids ) {
wfDebugLog( __CLASS__, __METHOD__ .
" master on '$cluster' failed locating items: " .
implode( ',', array_keys( $ids ) ) );
}
return $ret;
}
/**
* Helper function for self::batchFetchBlobs for merging master/replica DB results
* @param array &$ret Current self::batchFetchBlobs return value
* @param array &$ids Map from blob_id to requested itemIDs
* @param mixed $res DB result from Database::select
*/
private function mergeBatchResult( array &$ret, array &$ids, $res ) {
foreach ( $res as $row ) {
$id = $row->blob_id;
$itemIDs = $ids[$id];
unset( $ids[$id] ); // to track if everything is found
if ( count( $itemIDs ) === 1 && reset( $itemIDs ) === false ) {
// single result stored per blob
$ret[$id] = $row->blob_text;
} else {
// multi result stored per blob
$ret[$id] = unserialize( $row->blob_text );
}
}
}
/**
* @param string $url
* @return array
*/
protected function parseURL( $url ) {
$path = explode( '/', $url );
return [
$path[2], // cluster
$path[3], // id
$path[4] ?? false // itemID
];
}
}
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