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runBatchedQuery.php
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runBatchedQuery.php
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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.
*
* @license GPL-2.0-or-later
* @file
* @ingroup Maintenance
*/
// @codeCoverageIgnoreStart
require_once __DIR__ . '/Maintenance.php';
// @codeCoverageIgnoreEnd
use MediaWiki\Maintenance\Maintenance;
/**
* Maintenance script to run a database query in batches and wait for replica DBs.
*
* @ingroup Maintenance
*/
class RunBatchedQuery 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->getPrimaryDB();
} else {
$dbw = $this->getServiceContainer()->getConnectionProvider()->getPrimaryDatabase( $dbName );
}
$queryBuilder = $dbw->newSelectQueryBuilder()
->select( $key )
->from( $table )
->where( $where )
->caller( __METHOD__ );
$iterator = new BatchRowIterator( $dbw, $queryBuilder, $key, $batchSize );
foreach ( $iterator as $n => $batch ) {
$this->output( "Batch $n: " );
// Note that the update conditions do not rely on the 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.
$firstRow = reset( $batch );
$lastRow = end( $batch );
$dbw->newUpdateQueryBuilder()
->table( $table )
->set( $set )
->where( $where )
->andWhere( $dbw->expr( $key, '>=', $firstRow->$key ) )
->andWhere( $dbw->expr( $key, '<=', $lastRow->$key ) )
->caller( __METHOD__ )
->execute();
$affected = $dbw->affectedRows();
$this->output( "$affected rows affected\n" );
$this->waitForReplication();
}
}
/** @inheritDoc */
public function getDbType() {
return Maintenance::DB_ADMIN;
}
}
// @codeCoverageIgnoreStart
$maintClass = RunBatchedQuery::class;
require_once RUN_MAINTENANCE_IF_MAIN;
// @codeCoverageIgnoreEnd

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runBatchedQuery.php (2 KB)

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