includes/libs/rdbms/connectionmanager/SessionConsistentConnectionManager.php

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  11  * the replica databases are possibly outdated after a write operation, and thus the master database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