includes/libs/rdbms/connectionmanager/SessionConsistentConnectionManager.php

   1 <?php
   2 /**
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2 of the License, or
   6  * (at your option) any later version.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along
  14  * with this program; if not, write to the Free Software Foundation, Inc.,
  15  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  16  * http://www.gnu.org/copyleft/gpl.html
  17  *
  18  * @file
  19  */
  20 namespace Wikimedia\Rdbms;
  21
  22 /**
  23  * Database connection manager.
  24  *
  25  * This manages access to primary and replica databases. It also manages state that indicates whether
  26  * the replica databases are possibly outdated after a write operation, and thus the primary database
  27  * should be used for subsequent read operations.
  28  *
  29  * @note: Services that access overlapping sets of database tables, or interact with logically
  30  * related sets of data in the database, should share a SessionConsistentConnectionManager.
  31  * Services accessing unrelated sets of information may prefer to not share a
  32  * SessionConsistentConnectionManager, so they can still perform read operations against replica
  33  * databases after a (unrelated, per the assumption) write operation to the primary database.
  34  * Generally, sharing a SessionConsistentConnectionManager improves consistency (by avoiding race
  35  * conditions due to replication lag), but can reduce performance (by directing more read
  36  * operations to the primary database server).
  37  *
  38  * @since 1.29
  39  * @ingroup Database
  40  * @author Daniel Kinzler
  41  * @author Addshore
  42  */
  43 class SessionConsistentConnectionManager extends ConnectionManager {
  44
  45         /**
  46          * @var bool
  47          */
  48         private $forceWriteConnection = false;
  49
  50         /**
  51          * Forces all future calls to getReadConnection() to return a write connection.
  52          * Use this before performing read operations that are critical for a future update.
  53          *
  54          * @since 1.29
  55          */
  56         public function prepareForUpdates() {
  57                 $this->forceWriteConnection = true;
  58         }
  59
  60         /**
  61          * @since 1.29
  62          * @since 1.37 Added optional $flags parameter
  63          *
  64          * @param string[]|null $groups
  65          * @param int $flags
  66          *
  67          * @return IReadableDatabase
  68          */
  69         public function getReadConnection( ?array $groups = null, int $flags = 0 ) {
  70                 if ( $this->forceWriteConnection ) {
  71                         return parent::getWriteConnection( $flags );
  72                 }
  73
  74                 return parent::getReadConnection( $groups, $flags );
  75         }
  76
  77         /**
  78          * @since 1.29
  79          * @since 1.37 Added optional $flags parameter
  80          *
  81          * @param int $flags
  82          *
  83          * @return IDatabase
  84          */
  85         public function getWriteConnection( int $flags = 0 ) {
  86                 $this->prepareForUpdates();
  87                 return parent::getWriteConnection( $flags );
  88         }
  89
  90 }