From edda5eca4c41be467d8fc78764ab4355bb73f766 Mon Sep 17 00:00:00 2001
From: Tim Starling <tstarling@users.mediawiki.org>
Date: Fri, 26 Sep 2008 02:42:30 +0000
Subject: [PATCH] * Make Revision::newFromTitle() get the page_latest value
 from the master instead of the slave * Use inefficient replication-aware
 fetches only if replication is in use * Update docs/database.txt on how to
 check for replication

---
 docs/database.txt     |  4 ++--
 includes/Revision.php | 32 ++++++++++++++++++++------------
 2 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/docs/database.txt b/docs/database.txt
index 60e268c5b0..e80a494078 100644
--- a/docs/database.txt
+++ b/docs/database.txt
@@ -74,7 +74,7 @@ want to write code destined for Wikipedia.
 It's often the case that the best algorithm to use for a given task
 depends on whether or not replication is in use. Due to our unabashed
 Wikipedia-centrism, we often just use the replication-friendly version,
-but if you like, you can use $wgLoadBalancer->getServerCount() > 1 to
+but if you like, you can use wfGetLB()->getServerCount() > 1 to
 check to see if replication is in use.
 
 === Lag ===
@@ -110,7 +110,7 @@ in the session, and then at the start of each request, waiting for the
 slave to catch up to that position before doing any reads from it. If
 this wait times out, reads are allowed anyway, but the request is
 considered to be in "lagged slave mode". Lagged slave mode can be
-checked by calling $wgLoadBalancer->getLaggedSlaveMode(). The only
+checked by calling wfGetLB()->getLaggedSlaveMode(). The only
 practical consequence at present is a warning displayed in the page
 footer.
 
diff --git a/includes/Revision.php b/includes/Revision.php
index c369571ece..aa77bf963d 100644
--- a/includes/Revision.php
+++ b/includes/Revision.php
@@ -42,16 +42,24 @@ class Revision {
 	 * @return Revision
 	 */
 	public static function newFromTitle( $title, $id = 0 ) {
-		if( $id ) {
-			$matchId = intval( $id );
+		$conds = array( 
+			'page_namespace' => $title->getNamespace(), 
+			'page_title' => $title->getDBkey()
+		);
+		if ( $id ) {
+			// Use the specified ID
+			$conds['rev_id'] = $id;
+		} elseif ( wfGetLB()->getServerCount() > 1 ) {
+			// Get the latest revision ID from the master
+			$dbw = wfGetDB( DB_MASTER );
+			$latest = $dbw->selectField( 'page', 'page_latest', $conds, __METHOD__ );
+			$conds['rev_id'] = $latest;
 		} else {
-			$matchId = 'page_latest';
+			// Use a join to get the latest revision
+			$conds[] = 'rev_id=page_latest';
 		}
-		return Revision::newFromConds(
-			array( "rev_id=$matchId",
-			       'page_id=rev_page',
-			       'page_namespace' => $title->getNamespace(),
-			       'page_title'     => $title->getDBkey() ) );
+		$conds[] = 'page_id=rev_page';
+		return Revision::newFromConds( $conds );
 	}
 
 	/**
@@ -149,7 +157,7 @@ class Revision {
 	private static function newFromConds( $conditions ) {
 		$db = wfGetDB( DB_SLAVE );
 		$row = Revision::loadFromConds( $db, $conditions );
-		if( is_null( $row ) ) {
+		if( is_null( $row ) && wfGetLB()->getServerCount() > 1 ) {
 			$dbw = wfGetDB( DB_MASTER );
 			$row = Revision::loadFromConds( $dbw, $conditions );
 		}
@@ -237,7 +245,7 @@ class Revision {
 			array( 'page', 'revision' ),
 			$fields,
 			$conditions,
-			'Revision::fetchRow',
+			__METHOD__,
 			array( 'LIMIT' => 1 ) );
 		$ret = $db->resultObject( $res );
 		return $ret;
@@ -848,7 +856,7 @@ class Revision {
 				__METHOD__ );
 		}
 
-		if( !$row ) {
+		if( !$row && wfGetLB()->getServerCount() > 1 ) {
 			// Possible slave lag!
 			$dbw = wfGetDB( DB_MASTER );
 			$row = $dbw->selectRow( 'text',
@@ -945,7 +953,7 @@ class Revision {
 			$conds['rev_page'] = $pageId;
 		}
 		$timestamp = $dbr->selectField( 'revision', 'rev_timestamp', $conds, __METHOD__ );
-		if ( $timestamp === false ) {
+		if ( $timestamp === false && wfGetLB()->getServerCount() > 1 ) {
 			# Not in slave, try master
 			$dbw = wfGetDB( DB_MASTER );
 			$timestamp = $dbw->selectField( 'revision', 'rev_timestamp', $conds, __METHOD__ );
-- 
2.20.1