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<?php
/**
* Run a database query in batches and wait for replica DBs. This is used on large
* wikis to prevent replication lag from going through the roof when executing
* large write queries.
*
* 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
* @ingroup Maintenance
*/
require_once __DIR__ . '/Maintenance.php';
use Wikimedia\Rdbms\IDatabase;
/**
* Maintenance script to run a database query in batches and wait for replica DBs.
*
* @ingroup Maintenance
*/
class BatchedQueryRunner extends Maintenance {
public function __construct() {
parent::__construct();
$this->addDescription(
"Run an update query on all rows of a table. " .
"Waits for replicas at appropriate intervals." );
$this->addOption( 'table', 'The table name', true, true );
$this->addOption( 'set', 'The SET clause', true, true );
$this->addOption( 'where', 'The WHERE clause', false, true );
$this->addOption( 'key', 'A column name, the values of which are unique', true, true );
$this->addOption( 'batch-size', 'The batch size (default 1000)', false, true );
$this->addOption( 'db', 'The database name, or omit to use the current wiki.', false, true );
}
public function execute() {
$table = $this->getOption( 'table' );
$key = $this->getOption( 'key' );
$set = $this->getOption( 'set' );
$where = $this->getOption( 'where', null );
$where = $where === null ? [] : [ $where ];
$batchSize = $this->getOption( 'batch-size', 1000 );
$dbName = $this->getOption( 'db', null );
if ( $dbName === null ) {
$dbw = $this->getDB( DB_MASTER );
} else {
$lbf = MediaWiki\MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
$lb = $lbf->getMainLB( $dbName );
$dbw = $lb->getConnection( DB_MASTER, [], $dbName );
}
$selectConds = $where;
$prevEnd = false;
$n = 1;
do {
$this->output( "Batch $n: " );
$n++;
// Note that the update conditions do not rely on atomicity of the
// SELECT query in order to guarantee that all rows are updated. The
// results of the SELECT are merely a partitioning hint. Simultaneous
// updates merely result in the wrong number of rows being updated
// in a batch.
$res = $dbw->select( $table, $key, $selectConds, __METHOD__,
[ 'ORDER BY' => $key, 'LIMIT' => $batchSize ] );
if ( $res->numRows() ) {
$res->seek( $res->numRows() - 1 );
$row = $res->fetchObject();
$end = $dbw->addQuotes( $row->$key );
$selectConds = array_merge( $where, [ "$key > $end" ] );
$updateConds = array_merge( $where, [ "$key <= $end" ] );
} else {
$updateConds = $where;
}
if ( $prevEnd !== false ) {
$updateConds = array_merge( [ "$key > $prevEnd" ], $updateConds );
}
$query = "UPDATE " . $dbw->tableName( $table ) .
" SET " . $set .
" WHERE " . $dbw->makeList( $updateConds, IDatabase::LIST_AND );
$dbw->query( $query, __METHOD__ );
$prevEnd = $end;
$affected = $dbw->affectedRows();
$this->output( "$affected rows affected\n" );
wfWaitForSlaves();
} while ( $res->numRows() );
}
public function getDbType() {
return Maintenance::DB_ADMIN;
}
}
$maintClass = BatchedQueryRunner::class;
require_once RUN_MAINTENANCE_IF_MAIN;
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