From 01a5c6013e4a59815678b56bea21b94c0975d338 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Tue, 7 Apr 2015 11:04:17 -0700
Subject: [PATCH] Made wfReadOnly() more robust at handling the lagged-slave
 case

* Previously if it was called before a DB_SLAVE connection, it would not
  be set. This is fixed now.
* Also set mLaggedSlaveMode in LoadBalancer as appropriate. Before, it
  was only set in the "too lagged for ChronologyProtector" case.

Change-Id: Ic4dc555cf762653f157df1795f53f3577c1e587a
---
 includes/GlobalFunctions.php |  6 ++++++
 includes/db/LoadBalancer.php | 15 ++++++++++-----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/includes/GlobalFunctions.php b/includes/GlobalFunctions.php
index 7c4ebc27e2..3be43b39cc 100644
--- a/includes/GlobalFunctions.php
+++ b/includes/GlobalFunctions.php
@@ -1344,6 +1344,12 @@ function wfReadOnlyReason() {
 		} else {
 			$wgReadOnly = false;
 		}
+		// Callers use this method to be aware that data presented to a user
+		// may be very stale and thus allowing submissions can be problematic.
+		if ( $wgReadOnly === false && wfGetLB()->getLaggedSlaveMode() ) {
+			$wgReadOnly = 'The database has been automatically locked ' .
+				'while the slave database servers catch up to the master';
+		}
 	}
 
 	return $wgReadOnly;
diff --git a/includes/db/LoadBalancer.php b/includes/db/LoadBalancer.php
index d9584e147b..bc17911f9a 100644
--- a/includes/db/LoadBalancer.php
+++ b/includes/db/LoadBalancer.php
@@ -214,7 +214,7 @@ class LoadBalancer {
 	 * @return bool|int|string
 	 */
 	public function getReaderIndex( $group = false, $wiki = false ) {
-		global $wgReadOnly, $wgDBtype;
+		global $wgDBtype;
 
 		# @todo FIXME: For now, only go through all this for mysql databases
 		if ( $wgDBtype != 'mysql' ) {
@@ -258,7 +258,7 @@ class LoadBalancer {
 		# meets our criteria
 		$currentLoads = $nonErrorLoads;
 		while ( count( $currentLoads ) ) {
-			if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
+			if ( $this->mAllowLagged || $laggedSlaveMode ) {
 				$i = ArrayUtils::pickRandom( $currentLoads );
 			} else {
 				$i = false;
@@ -277,8 +277,6 @@ class LoadBalancer {
 				if ( $i === false && count( $currentLoads ) != 0 ) {
 					# All slaves lagged. Switch to read-only mode
 					wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
-					$wgReadOnly = 'The database has been automatically locked ' .
-						'while the slave database servers catch up to the master';
 					$i = ArrayUtils::pickRandom( $currentLoads );
 					$laggedSlaveMode = true;
 				}
@@ -330,6 +328,10 @@ class LoadBalancer {
 			}
 			if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 				$this->mReadIndex = $i;
+				# Record if the generic reader index is in "lagged slave" mode
+				if ( $laggedSlaveMode ) {
+					$this->mLaggedSlaveMode = true;
+				}
 			}
 			$serverName = $this->getServerName( $i );
 			wfDebug( __METHOD__ . ": using server $serverName for group '$group'\n" );
@@ -1096,9 +1098,12 @@ class LoadBalancer {
 	}
 
 	/**
-	 * @return bool
+	 * @return bool Whether the generic connection for reads is highly "lagged"
 	 */
 	public function getLaggedSlaveMode() {
+		# Get a generic reader connection
+		$this->getConnection( DB_SLAVE );
+
 		return $this->mLaggedSlaveMode;
 	}
 
-- 
2.20.1