includes/libs/rdbms/connectionmanager/SessionConsistentConnectionManager.php

   1 <?php
   2
   3 namespace Wikimedia\Rdbms;
   4
   5 use Database;
   6 use DBConnRef;
   7
   8 /**
   9  * Database connection manager.
  10  *
  11  * This manages access to master and replica databases. It also manages state that indicates whether
  12  * the replica databases are possibly outdated after a write operation, and thus the master database
  13  * should be used for subsequent read operations.
  14  *
  15  * @note: Services that access overlapping sets of database tables, or interact with logically
  16  * related sets of data in the database, should share a SessionConsistentConnectionManager.
  17  * Services accessing unrelated sets of information may prefer to not share a
  18  * SessionConsistentConnectionManager, so they can still perform read operations against replica
  19  * databases after a (unrelated, per the assumption) write operation to the master database.
  20  * Generally, sharing a SessionConsistentConnectionManager improves consistency (by avoiding race
  21  * conditions due to replication lag), but can reduce performance (by directing more read
  22  * operations to the master database server).
  23  *
  24  * @since 1.29
  25  *
  26  * @license GPL-2.0+
  27  * @author Daniel Kinzler
  28  * @author Addshore
  29  */
  30 class SessionConsistentConnectionManager extends ConnectionManager {
  31
  32         /**
  33          * @var bool
  34          */
  35         private $forceWriteConnection = false;
  36
  37         /**
  38          * Forces all future calls to getReadConnection() to return a write connection.
  39          * Use this before performing read operations that are critical for a future update.
  40          *
  41          * @since 1.29
  42          */
  43         public function prepareForUpdates() {
  44                 $this->forceWriteConnection = true;
  45         }
  46
  47         /**
  48          * @since 1.29
  49          *
  50          * @param string[]|null $groups
  51          *
  52          * @return Database
  53          */
  54         public function getReadConnection( array $groups = null ) {
  55                 if ( $this->forceWriteConnection ) {
  56                         return parent::getWriteConnection();
  57                 }
  58
  59                 return parent::getReadConnection( $groups );
  60         }
  61
  62         /**
  63          * @since 1.29
  64          *
  65          * @return Database
  66          */
  67         public function getWriteConnection() {
  68                 $this->prepareForUpdates();
  69                 return parent::getWriteConnection();
  70         }
  71
  72         /**
  73          * @since 1.29
  74          *
  75          * @param string[]|null $groups
  76          *
  77          * @return DBConnRef
  78          */
  79         public function getReadConnectionRef( array $groups = null ) {
  80                 if ( $this->forceWriteConnection ) {
  81                         return parent::getWriteConnectionRef();
  82                 }
  83
  84                 return parent::getReadConnectionRef( $groups );
  85         }
  86
  87         /**
  88          * @since 1.29
  89          *
  90          * @return DBConnRef
  91          */
  92         public function getWriteConnectionRef() {
  93                 $this->prepareForUpdates();
  94                 return parent::getWriteConnectionRef();
  95         }
  96
  97 }