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  * @ingroup Database
  20  */
  21
  22 namespace Wikimedia\Rdbms;
  23
  24 /**
  25  * Database connection manager.
  26  *
  27  * This manages access to master and replica databases. It also manages state that indicates whether
  28  * the replica databases are possibly outdated after a write operation, and thus the master database
  29  * should be used for subsequent read operations.
  30  *
  31  * @note: Services that access overlapping sets of database tables, or interact with logically
  32  * related sets of data in the database, should share a SessionConsistentConnectionManager.
  33  * Services accessing unrelated sets of information may prefer to not share a
  34  * SessionConsistentConnectionManager, so they can still perform read operations against replica
  35  * databases after a (unrelated, per the assumption) write operation to the master database.
  36  * Generally, sharing a SessionConsistentConnectionManager improves consistency (by avoiding race
  37  * conditions due to replication lag), but can reduce performance (by directing more read
  38  * operations to the master database server).
  39  *
  40  * @since 1.29
  41  *
  42  * @author Daniel Kinzler
  43  * @author Addshore
  44  */
  45 class SessionConsistentConnectionManager extends ConnectionManager {
  46
  47         /**
  48          * @var bool
  49          */
  50         private $forceWriteConnection = false;
  51
  52         /**
  53          * Forces all future calls to getReadConnection() to return a write connection.
  54          * Use this before performing read operations that are critical for a future update.
  55          *
  56          * @since 1.29
  57          */
  58         public function prepareForUpdates() {
  59                 $this->forceWriteConnection = true;
  60         }
  61
  62         /**
  63          * @since 1.29
  64          *
  65          * @param string[]|null $groups
  66          *
  67          * @return IDatabase
  68          */
  69         public function getReadConnection( array $groups = null ) {
  70                 if ( $this->forceWriteConnection ) {
  71                         return parent::getWriteConnection();
  72                 }
  73
  74                 return parent::getReadConnection( $groups );
  75         }
  76
  77         /**
  78          * @since 1.29
  79          *
  80          * @return IDatabase
  81          */
  82         public function getWriteConnection() {
  83                 $this->prepareForUpdates();
  84                 return parent::getWriteConnection();
  85         }
  86
  87         /**
  88          * @since 1.29
  89          *
  90          * @param string[]|null $groups
  91          *
  92          * @return DBConnRef
  93          */
  94         public function getReadConnectionRef( array $groups = null ) {
  95                 if ( $this->forceWriteConnection ) {
  96                         return parent::getWriteConnectionRef();
  97                 }
  98
  99                 return parent::getReadConnectionRef( $groups );
 100         }
 101
 102         /**
 103          * @since 1.29
 104          *
 105          * @return DBConnRef
 106          */
 107         public function getWriteConnectionRef() {
 108                 $this->prepareForUpdates();
 109                 return parent::getWriteConnectionRef();
 110         }
 111
 112 }