includes/libs/rdbms/connectionmanager/SessionConsistentConnectionManager.php

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   9  * the replica databases are possibly outdated after a write operation, and thus the master database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