From df4ad11d29e1fd96e9dc313a25559658e49b7f0f Mon Sep 17 00:00:00 2001
From: Tim Starling <tstarling@users.mediawiki.org>
Date: Mon, 5 Mar 2007 12:42:19 +0000
Subject: [PATCH] Bringing foreign connection logic into the core. Committing
 for test on server.

---
 includes/DefaultSettings.php |  8 ++++++
 includes/LoadBalancer.php    | 52 +++++++++++++++++++++++++++++++++++-
 2 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/includes/DefaultSettings.php b/includes/DefaultSettings.php
index 690d9c2acd..98b94d4b5f 100644
--- a/includes/DefaultSettings.php
+++ b/includes/DefaultSettings.php
@@ -592,6 +592,14 @@ $wgDBmysql5			= false;
  */
 $wgLocalDatabases   = array();
 
+/**
+ * A map of database name (key) to connection index (value), describing the 
+ * master database server for each database. The connection index is an 
+ * index into the $wgDBservers array. If a database is not listed here, the
+ * default load balancing settings will be used.
+ */
+$wgAlternateMaster = array();
+
 /**
  * Object cache settings
  * See Defines.php for types
diff --git a/includes/LoadBalancer.php b/includes/LoadBalancer.php
index d3d072eed3..b9fda222e5 100644
--- a/includes/LoadBalancer.php
+++ b/includes/LoadBalancer.php
@@ -240,6 +240,53 @@ class LoadBalancer {
 		return $i;
 	}
 
+	/**
+	 * Get a connection to a foreign DB. Will use the following types of 
+	 * connection in order of precedence:
+	 *    * The alternate master, if there is one and DB_MASTER is given
+	 *    * The query group
+	 *    * The alternate master, if there is one
+	 *    * The default writer, if DB_MASTER was specified
+	 *    * The default reader. 
+	 * 
+	 * Connection error will *not* lead to progression down this list. Selection
+	 * of a group depends only on configuration.
+	 *
+	 * @param string $dbName The database name
+	 * @param mixed $group The query group, or DB_MASTER for the foreign master
+	 * @return Database object with the database selected
+	 */
+	function getForeignConnection( $dbName, $group = false ) {
+		global $wgAlternateMaster;
+
+		// Try cache
+		if ( isset( $this->mForeignConnections[$dbName][$group] ) ) {
+			return $this->mForeignConnections[$dbName][$group];
+		}
+
+		// Try the precedence list described in the function description
+		if ( $group === DB_MASTER && isset( $wgAlternateMaster[$dbName] ) ) {
+			$index = $this->mServers[$wgAlternateMaster[$dbName]];
+		} if ( $group && $group !== DB_MASTER ) {
+			$index = $this->getGroupIndex( $group );
+		} elseif ( isset( $wgAlternateMaster[$dbName] ) ) {
+			$index = $this->mServers[$wgAlternateMaster[$dbName]];
+		} elseif ( $group === DB_MASTER ) {
+			$index = $this->getWriterIndex();
+		} else {
+			$index = $this->getReaderIndex();
+		}
+
+		if ( $index === false || !isset( $this->mServers[$index] ) ) {
+			throw new MWException( "No configured server available for foreign connection to $dbName" );
+		}
+
+		$dbInfo = $this->mServers[$index];
+		$dbc = $this->reallyOpenConnection( $dbInfo, $dbName );
+		$this->mForeignConnections[$dbName][$group] = $dbc;
+		return $dbc;
+	}
+
 	/**
 	 * Set the master wait position
 	 * If a DB_SLAVE connection has been opened already, waits
@@ -415,12 +462,15 @@ class LoadBalancer {
 	 * Really opens a connection
 	 * @access private
 	 */
-	function reallyOpenConnection( &$server ) {
+	function reallyOpenConnection( &$server, $overrideDBname = false ) {
 		if( !is_array( $server ) ) {
 			throw new MWException( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
 		}
 
 		extract( $server );
+		if ( $overrideDBname ) {
+			$dbname = $overrideDBname;
+		}
 		# Get class for this database type
 		$class = 'Database' . ucfirst( $type );
 
-- 
2.20.1