MediaWiki 1.30.2

[autoinstallsdev/mediawiki.git] / includes / libs / rdbms / connectionmanager / SessionConsistentConnectionManager.php

diff --git a/includes/libs/rdbms/connectionmanager/SessionConsistentConnectionManager.php b/includes/libs/rdbms/connectionmanager/SessionConsistentConnectionManager.php
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+<?php
+
+namespace Wikimedia\Rdbms;
+
+/**
+ * Database connection manager.
+ *
+ * This manages access to master and replica databases. It also manages state that indicates whether
+ * the replica databases are possibly outdated after a write operation, and thus the master database
+ * should be used for subsequent read operations.
+ *
+ * @note: Services that access overlapping sets of database tables, or interact with logically
+ * related sets of data in the database, should share a SessionConsistentConnectionManager.
+ * Services accessing unrelated sets of information may prefer to not share a
+ * SessionConsistentConnectionManager, so they can still perform read operations against replica
+ * databases after a (unrelated, per the assumption) write operation to the master database.
+ * Generally, sharing a SessionConsistentConnectionManager improves consistency (by avoiding race
+ * conditions due to replication lag), but can reduce performance (by directing more read
+ * operations to the master database server).
+ *
+ * @since 1.29
+ *
+ * @license GPL-2.0+
+ * @author Daniel Kinzler
+ * @author Addshore
+ */
+class SessionConsistentConnectionManager extends ConnectionManager {
+
+       /**
+        * @var bool
+        */
+       private $forceWriteConnection = false;
+
+       /**
+        * Forces all future calls to getReadConnection() to return a write connection.
+        * Use this before performing read operations that are critical for a future update.
+        *
+        * @since 1.29
+        */
+       public function prepareForUpdates() {
+               $this->forceWriteConnection = true;
+       }
+
+       /**
+        * @since 1.29
+        *
+        * @param string[]|null $groups
+        *
+        * @return Database
+        */
+       public function getReadConnection( array $groups = null ) {
+               if ( $this->forceWriteConnection ) {
+                       return parent::getWriteConnection();
+               }
+
+               return parent::getReadConnection( $groups );
+       }
+
+       /**
+        * @since 1.29
+        *
+        * @return Database
+        */
+       public function getWriteConnection() {
+               $this->prepareForUpdates();
+               return parent::getWriteConnection();
+       }
+
+       /**
+        * @since 1.29
+        *
+        * @param string[]|null $groups
+        *
+        * @return DBConnRef
+        */
+       public function getReadConnectionRef( array $groups = null ) {
+               if ( $this->forceWriteConnection ) {
+                       return parent::getWriteConnectionRef();
+               }
+
+               return parent::getReadConnectionRef( $groups );
+       }
+
+       /**
+        * @since 1.29
+        *
+        * @return DBConnRef
+        */
+       public function getWriteConnectionRef() {
+               $this->prepareForUpdates();
+               return parent::getWriteConnectionRef();
+       }
+
+}