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 slave databases. It also manages state that indicates whether
  12  * the slave databases are possibly outdated after a write operation, and thus the master database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 slave
  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          * Calling beginAtomicSection() implies a call to prepareForUpdates().
  41          *
  42          * @since 1.29
  43          */
  44         public function prepareForUpdates() {
  45                 $this->forceWriteConnection = true;
  46         }
  47
  48         /**
  49          * @since 1.29
  50          *
  51          * @param string[]|null $groups
  52          *
  53          * @return Database
  54          */
  55         public function getReadConnection( array $groups = null ) {
  56                 if ( $this->forceWriteConnection ) {
  57                         return parent::getWriteConnection();
  58                 }
  59
  60                 return parent::getReadConnection( $groups );
  61         }
  62
  63         /**
  64          * @since 1.29
  65          *
  66          * @return Database
  67          */
  68         public function getWriteConnection() {
  69                 $this->prepareForUpdates();
  70                 return parent::getWriteConnection();
  71         }
  72
  73         /**
  74          * @since 1.29
  75          *
  76          * @param string[]|null $groups
  77          *
  78          * @return DBConnRef
  79          */
  80         public function getReadConnectionRef( array $groups = null ) {
  81                 if ( $this->forceWriteConnection ) {
  82                         return parent::getWriteConnectionRef();
  83                 }
  84
  85                 return parent::getReadConnectionRef( $groups );
  86         }
  87
  88         /**
  89          * @since 1.29
  90          *
  91          * @return DBConnRef
  92          */
  93         public function getWriteConnectionRef() {
  94                 $this->prepareForUpdates();
  95                 return parent::getWriteConnectionRef();
  96         }
  97
  98         /**
  99          * Begins an atomic section and returns a database connection to the master DB, for updating.
 100          *
 101          * @since 1.29
 102          *
 103          * @note: This causes all future calls to getReadConnection() to return a connection
 104          * to the master DB, even after commitAtomicSection() or rollbackAtomicSection() have
 105          * been called.
 106          *
 107          * @param string $fname
 108          *
 109          * @return Database
 110          */
 111         public function beginAtomicSection( $fname ) {
 112                 // Once we have written to master, do not read from replica.
 113                 $this->prepareForUpdates();
 114
 115                 return parent::beginAtomicSection( $fname );
 116         }
 117
 118 }