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ExternalStoreDB.php
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ExternalStoreDB.php
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<?php
/**
* 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 Wikimedia\Rdbms\DatabaseDomain;
use Wikimedia\Rdbms\DBUnexpectedError;
use Wikimedia\Rdbms\ILoadBalancer;
use Wikimedia\Rdbms\LBFactory;
use Wikimedia\Rdbms\Query;
use Wikimedia\Rdbms\ServerInfo;
use Wikimedia\ScopedCallback;
/**
* External storage in a SQL database.
*
* In this system, each store "location" maps to a database "cluster".
* The clusters must be defined in the normal LBFactory configuration.
*
* @see ExternalStoreAccess
* @ingroup ExternalStorage
*/
class ExternalStoreDB extends ExternalStoreMedium {
/** @var LBFactory */
private $lbFactory;
/**
* @see ExternalStoreMedium::__construct()
* @param array $params Additional parameters include:
* - lbFactory: an LBFactory instance
*/
public function __construct( array $params ) {
parent::__construct( $params );
if ( !isset( $params['lbFactory'] ) || !( $params['lbFactory'] instanceof LBFactory ) ) {
throw new InvalidArgumentException( "LBFactory required in 'lbFactory' field." );
}
$this->lbFactory = $params['lbFactory'];
}
/**
* Fetch data from given external store URL.
*
* The provided URL is in the form of `DB://cluster/id` or `DB://cluster/id/itemid`
* for concatenated storage if ConcatenatedGzipHistoryBlob was used.
*
* @param string $url
* @return string|false False if missing
* @see ExternalStoreMedium::fetchFromURL()
*/
public function fetchFromURL( $url ) {
[ $cluster, $id, $itemID ] = $this->parseURL( $url );
$ret = $this->fetchBlob( $cluster, $id, $itemID );
if ( $itemID !== false && $ret !== false ) {
return $ret->getItem( $itemID );
}
return $ret;
}
/**
* Fetch multiple URLs from given external store.
*
* The provided URLs are in the form of `DB://cluster/id`, or `DB://cluster/id/itemid`
* for concatenated storage if ConcatenatedGzipHistoryBlob was used.
*
* @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 ) {
[ $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;
}
/**
* @inheritDoc
*/
public function store( $location, $data ) {
$blobsTable = $this->getTable( $location );
$dbw = $this->getPrimary( $location );
$dbw->newInsertQueryBuilder()
->insertInto( $blobsTable )
->row( [ 'blob_text' => $data ] )
->caller( __METHOD__ )->execute();
$id = $dbw->insertId();
if ( !$id ) {
throw new ExternalStoreException( __METHOD__ . ': no insert ID' );
}
return "DB://$location/$id";
}
/**
* @inheritDoc
*/
public function isReadOnly( $location ) {
if ( parent::isReadOnly( $location ) ) {
return true;
}
return ( $this->getLoadBalancer( $location )->getReadOnlyReason() !== false );
}
/**
* Get a LoadBalancer for the specified cluster
*
* @param string $cluster Cluster name
* @return ILoadBalancer
*/
private function getLoadBalancer( $cluster ) {
return $this->lbFactory->getExternalLB( $cluster );
}
/**
* Get a replica DB connection for the specified cluster
*
* @since 1.34
* @param string $cluster Cluster name
* @return \Wikimedia\Rdbms\IReadableDatabase
*/
public function getReplica( $cluster ) {
$lb = $this->getLoadBalancer( $cluster );
return $lb->getConnection(
DB_REPLICA,
[],
$this->getDomainId( $lb->getServerInfo( ServerInfo::WRITER_INDEX ) ),
$lb::CONN_TRX_AUTOCOMMIT
);
}
/**
* Get a primary database connection for the specified cluster
*
* @param string $cluster Cluster name
* @return \Wikimedia\Rdbms\IMaintainableDatabase
* @since 1.37
*/
public function getPrimary( $cluster ) {
$lb = $this->getLoadBalancer( $cluster );
return $lb->getMaintenanceConnectionRef(
DB_PRIMARY,
[],
$this->getDomainId( $lb->getServerInfo( ServerInfo::WRITER_INDEX ) ),
$lb::CONN_TRX_AUTOCOMMIT
);
}
/**
* @param array $server Primary DB server configuration array for LoadBalancer
* @return string|false Database domain ID or false
*/
private function getDomainId( array $server ) {
if ( $this->isDbDomainExplicit ) {
return $this->dbDomain; // explicit foreign 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 configured blobs table name for this database
*
* Typically, a suffix like "_clusterX" can be used to facilitate clean merging of
* read-only storage clusters by simply cloning tables to the new cluster servers.
*
* @param string $cluster Cluster name
* @return string Unqualified table name (e.g. "blobs_cluster32" or default "blobs")
* @internal Only for use within ExternalStoreDB and its core maintenance scripts
*/
public function getTable( string $cluster ) {
$lb = $this->getLoadBalancer( $cluster );
$info = $lb->getServerInfo( ServerInfo::WRITER_INDEX );
return $info['blobs table'] ?? 'blobs';
}
/**
* Create the appropriate blobs table on this cluster
*
* @since 1.34
* @param string $cluster
*/
public function initializeTable( $cluster ) {
global $IP;
static $supportedTypes = [ 'mysql', 'sqlite' ];
$dbw = $this->getPrimary( $cluster );
if ( !in_array( $dbw->getType(), $supportedTypes, true ) ) {
throw new DBUnexpectedError( $dbw, "RDBMS type '{$dbw->getType()}' not supported." );
}
$sqlFilePath = "$IP/maintenance/storage/blobs.sql";
$sql = file_get_contents( $sqlFilePath );
if ( $sql === false ) {
throw new RuntimeException( "Failed to read '$sqlFilePath'." );
}
$blobsTable = $this->getTable( $cluster );
$encTable = $dbw->tableName( $blobsTable );
$sqlWithReplacedVars = str_replace(
[ '/*$wgDBprefix*/blobs', '/*_*/blobs' ],
[ $encTable, $encTable ],
$sql
);
$dbw->query(
new Query(
$sqlWithReplacedVars,
$dbw::QUERY_CHANGE_SCHEMA,
'CREATE',
$blobsTable,
$sqlWithReplacedVars
),
__METHOD__
);
}
/**
* 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|false 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/";
$cacheID = "$cacheID@{$this->dbDomain}";
if ( isset( $externalBlobCache[$cacheID] ) ) {
$this->logger->debug( __METHOD__ . ": cache hit on $cacheID" );
return $externalBlobCache[$cacheID];
}
$this->logger->debug( __METHOD__ . ": cache miss on $cacheID" );
$blobsTable = $this->getTable( $cluster );
$dbr = $this->getReplica( $cluster );
$ret = $dbr->newSelectQueryBuilder()
->select( 'blob_text' )
->from( $blobsTable )
->where( [ 'blob_id' => $id ] )
->caller( __METHOD__ )->fetchField();
if ( $ret === false ) {
// Try the primary DB
$this->logger->warning( __METHOD__ . ": primary DB fallback on $cacheID" );
$trxProfiler = $this->lbFactory->getTransactionProfiler();
$scope = $trxProfiler->silenceForScope( $trxProfiler::EXPECTATION_REPLICAS_ONLY );
$dbw = $this->getPrimary( $cluster );
$ret = $dbw->newSelectQueryBuilder()
->select( 'blob_text' )
->from( $blobsTable )
->where( [ 'blob_id' => $id ] )
->caller( __METHOD__ )->fetchField();
ScopedCallback::consume( $scope );
if ( $ret === false ) {
$this->logger->warning( __METHOD__ . ": primary DB failed to find $cacheID" );
}
}
if ( $itemID !== false && $ret !== false ) {
// Unserialise object; caller extracts item
$ret = HistoryBlobUtils::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 ) {
$blobsTable = $this->getTable( $cluster );
$dbr = $this->getReplica( $cluster );
$res = $dbr->newSelectQueryBuilder()
->select( [ 'blob_id', 'blob_text' ] )
->from( $blobsTable )
->where( [ 'blob_id' => array_keys( $ids ) ] )
->caller( __METHOD__ )
->fetchResultSet();
$ret = [];
$this->mergeBatchResult( $ret, $ids, $res );
if ( $ids ) {
// Try the primary
$this->logger->info(
__METHOD__ . ": primary fallback on '$cluster' for: " .
implode( ',', array_keys( $ids ) )
);
$trxProfiler = $this->lbFactory->getTransactionProfiler();
$scope = $trxProfiler->silenceForScope( $trxProfiler::EXPECTATION_REPLICAS_ONLY );
$dbw = $this->getPrimary( $cluster );
$res = $dbw->newSelectQueryBuilder()
->select( [ 'blob_id', 'blob_text' ] )
->from( $blobsTable )
->where( [ 'blob_id' => array_keys( $ids ) ] )
->caller( __METHOD__ )
->fetchResultSet();
ScopedCallback::consume( $scope );
$this->mergeBatchResult( $ret, $ids, $res );
}
if ( $ids ) {
$this->logger->error(
__METHOD__ . ": primary on '$cluster' failed locating items: " .
implode( ',', array_keys( $ids ) )
);
}
return $ret;
}
/**
* Helper function for self::batchFetchBlobs for merging primary/replica DB results
* @param array &$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] = HistoryBlobUtils::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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Wed, Aug 19, 00:05 (2 d, 21 h ago)
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ExternalStoreDB.php (12 KB)

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