From 23f8346ce73875f8d78b07b067c19198c710eefa Mon Sep 17 00:00:00 2001
From: Tim Starling <tstarling@users.mediawiki.org>
Date: Mon, 29 Aug 2011 05:04:55 +0000
Subject: [PATCH] Further updates for r90643/r95647 in core and extensions.
 Fixed all callers of Database::getLag(), made them call a new function
 LoadBalancer::safeGetLag() instead, which doesn't cause fatal errors for
 non-replicated installations. The core updates are tested but the extension
 updates aren't.

---
 includes/db/Database.php                      |  8 ++++++--
 includes/db/LoadBalancer.php                  | 19 +++++++++++++++++++
 includes/specials/SpecialContributions.php    |  3 ++-
 .../specials/SpecialDeletedContributions.php  |  3 ++-
 includes/specials/SpecialWatchlist.php        |  2 +-
 5 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/includes/db/Database.php b/includes/db/Database.php
index 6126b3559b..c5b58e5a79 100644
--- a/includes/db/Database.php
+++ b/includes/db/Database.php
@@ -2980,8 +2980,12 @@ abstract class DatabaseBase implements DatabaseType {
 	}
 
 	/**
-	 * Get slave lag.
-	 * Currently supported only by MySQL
+	 * Get slave lag. Currently supported only by MySQL.
+	 *
+	 * Note that this function will generate a fatal error on many 
+	 * installations. Most callers should use LoadBalancer::safeGetLag() 
+	 * instead.
+	 *
 	 * @return Database replication lag in seconds
 	 */
 	function getLag() {
diff --git a/includes/db/LoadBalancer.php b/includes/db/LoadBalancer.php
index 55a6cee772..da26417768 100644
--- a/includes/db/LoadBalancer.php
+++ b/includes/db/LoadBalancer.php
@@ -987,6 +987,25 @@ class LoadBalancer {
 		return $this->mLagTimes;
 	}
 
+	/**
+	 * Get the lag in seconds for a given connection, or zero if this load 
+	 * balancer does not have replication enabled. 
+	 *
+	 * This should be used in preference to Database::getLag() in cases where 
+	 * replication may not be in use, since there is no way to determine if 
+	 * replication is in use at the connection level without running 
+	 * potentially restricted queries such as SHOW SLAVE STATUS. Using this
+	 * function instead of Database::getLag() avoids a fatal error in this
+	 * case on many installations.
+	 */
+	function safeGetLag( $conn ) {
+		if ( $this->getServerCount() == 1 ) {
+			return 0;
+		} else {
+			return $conn->getLag();
+		}
+	}
+
 	/**
 	 * Clear the cache for getLagTimes
 	 */
diff --git a/includes/specials/SpecialContributions.php b/includes/specials/SpecialContributions.php
index d724cb4fde..497bd1c846 100644
--- a/includes/specials/SpecialContributions.php
+++ b/includes/specials/SpecialContributions.php
@@ -167,7 +167,8 @@ class SpecialContributions extends SpecialPage {
 				$wgOut->addWikiMsg( 'nocontribs', $target );
 			} else {
 				# Show a message about slave lag, if applicable
-				if( ( $lag = $pager->getDatabase()->getLag() ) > 0 )
+				$lag = wfGetLB()->safeGetLag( $pager->getDatabase() );
+				if( $lag > 0 )
 					$wgOut->showLagWarning( $lag );
 
 				$wgOut->addHTML(
diff --git a/includes/specials/SpecialDeletedContributions.php b/includes/specials/SpecialDeletedContributions.php
index e45e85fd5b..265de421d4 100644
--- a/includes/specials/SpecialDeletedContributions.php
+++ b/includes/specials/SpecialDeletedContributions.php
@@ -317,7 +317,8 @@ class DeletedContributionsPage extends SpecialPage {
 		}
 
 		# Show a message about slave lag, if applicable
-		if( ( $lag = $pager->getDatabase()->getLag() ) > 0 )
+		$lag = wfGetLB()->safeGetLag( $pager->getDatabase() );
+		if( $lag > 0 )
 			$wgOut->showLagWarning( $lag );
 
 		$wgOut->addHTML(
diff --git a/includes/specials/SpecialWatchlist.php b/includes/specials/SpecialWatchlist.php
index fb57baa237..51086bb1b3 100644
--- a/includes/specials/SpecialWatchlist.php
+++ b/includes/specials/SpecialWatchlist.php
@@ -240,7 +240,7 @@ class SpecialWatchlist extends SpecialPage {
 		}
 
 		# Show a message about slave lag, if applicable
-		$lag = $dbr->getLag();
+		$lag = wfGetLB()->safeGetLag( $dbr );
 		if( $lag > 0 ) {
 			$output->showLagWarning( $lag );
 		}
-- 
2.20.1