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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
*/
namespace Wikimedia\Rdbms;
/**
* Database connection manager.
*
* This manages access to primary and replica databases. It also manages state that indicates whether
* the replica databases are possibly outdated after a write operation, and thus the primary database
* should be used for subsequent read operations.
*
* @note: Services that access overlapping sets of database tables, or interact with logically
* related sets of data in the database, should share a SessionConsistentConnectionManager.
* Services accessing unrelated sets of information may prefer to not share a
* SessionConsistentConnectionManager, so they can still perform read operations against replica
* databases after a (unrelated, per the assumption) write operation to the primary database.
* Generally, sharing a SessionConsistentConnectionManager improves consistency (by avoiding race
* conditions due to replication lag), but can reduce performance (by directing more read
* operations to the primary database server).
*
* @since 1.29
* @ingroup Database
* @author Daniel Kinzler
* @author Addshore
*/
class SessionConsistentConnectionManager extends ConnectionManager {
/**
* @var bool
*/
private $forceWriteConnection = false;
/**
* Forces all future calls to getReadConnection() to return a write connection.
* Use this before performing read operations that are critical for a future update.
*
* @since 1.29
*/
public function prepareForUpdates() {
$this->forceWriteConnection = true;
}
/**
* @since 1.29
* @since 1.37 Added optional $flags parameter
*
* @param string[]|null $groups
* @param int $flags
*
* @return IReadableDatabase
*/
public function getReadConnection( ?array $groups = null, int $flags = 0 ) {
if ( $this->forceWriteConnection ) {
return parent::getWriteConnection( $flags );
}
return parent::getReadConnection( $groups, $flags );
}
/**
* @since 1.29
* @since 1.37 Added optional $flags parameter
*
* @param int $flags
*
* @return IDatabase
*/
public function getWriteConnection( int $flags = 0 ) {
$this->prepareForUpdates();
return parent::getWriteConnection( $flags );
}
}
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