From: Tim Starling <tstarling@users.mediawiki.org>
Date: Mon, 29 Aug 2011 04:42:26 +0000 (+0000)
Subject: * Fix for r90643: in the case where there is only one server, implying no replication... 
X-Git-Tag: 1.31.0-rc.0~28031
X-Git-Url: http://git.cyclocoop.org/%22%20.%20generer_url_ecrire%28%22suivi_revisions%22%29%20.%20%22?a=commitdiff_plain;h=a3bf5ecb4a775cc319f0f26ab39a3dec350af846;p=lhc%2Fweb%2Fwiklou.git

* Fix for r90643: in the case where there is only one server, implying no replication, make LoadBalancer::getLagTimes(), LoadMonitor_MySQL::getLagTimes() and LoadBalancer::getMaxLag() quickly report zero lag without attempting to do a SHOW SLAVE STATUS query.
* Updated the documentation to make it clear that REPLICATION CLIENT is required in a replicated setup.
* Reverted r90773.
---

diff --git a/RELEASE-NOTES-1.18 b/RELEASE-NOTES-1.18
index c53d9b8d86..b1845f7fa2 100644
--- a/RELEASE-NOTES-1.18
+++ b/RELEASE-NOTES-1.18
@@ -177,8 +177,11 @@ production.
 * (bug 29441) Expose CapitalLinks config in JS to allow modules to properly
   handle titles on case-sensitive wikis.
 * (bug 29397) Implement mw.Title module in core.
-* In MySQL 4.1.9+ with replication enabled, the slave lag should come from
-  SHOW SLAVE STATUS instead of SHOW PROCESSLIST.
+* In MySQL 4.1.9+ with replication enabled, fetch the slave lag from SHOW SLAVE 
+  STATUS instead of SHOW PROCESSLIST. This ensures that lag is reported 
+  correctly in the case where there are no write events occurring. Note that 
+  the DB user now needs to have the REPLICATION CLIENT privilege if you are 
+  using replication.
 * Language codes in $wgDummyLanguageCodes are now excluded on localization
   statistics (maintenance/language/transstat.php)
 * (bug 29586) Make the (next 200) links on categories link directly to
diff --git a/includes/db/DatabaseMysql.php b/includes/db/DatabaseMysql.php
index 53adea11e0..314b6edd8b 100644
--- a/includes/db/DatabaseMysql.php
+++ b/includes/db/DatabaseMysql.php
@@ -376,9 +376,9 @@ class DatabaseMysql extends DatabaseBase {
 			return $this->mFakeSlaveLag;
 		}
 
-		/*if ( version_compare( $this->getServerVersion(), '4.1.9', '>=' ) ) {
+		if ( version_compare( $this->getServerVersion(), '4.1.9', '>=' ) ) {
 			return $this->getLagFromSlaveStatus();
-		} else */{
+		} else {
 			return $this->getLagFromProcesslist();
 		}
 	}
diff --git a/includes/db/LoadBalancer.php b/includes/db/LoadBalancer.php
index 506ceb98bb..55a6cee772 100644
--- a/includes/db/LoadBalancer.php
+++ b/includes/db/LoadBalancer.php
@@ -929,7 +929,9 @@ class LoadBalancer {
 	/**
 	 * Get the hostname and lag time of the most-lagged slave.
 	 * This is useful for maintenance scripts that need to throttle their updates.
-	 * May attempt to open connections to slaves on the default DB.
+	 * May attempt to open connections to slaves on the default DB. If there is 
+	 * no lag, the maximum lag will be reported as -1.
+	 *
 	 * @param $wiki string Wiki ID, or false for the default database
 	 *
 	 * @return array ( host, max lag, index of max lagged host )
@@ -938,22 +940,24 @@ class LoadBalancer {
 		$maxLag = -1;
 		$host = '';
 		$maxIndex = 0;
-		foreach ( $this->mServers as $i => $conn ) {
-			$conn = false;
-			if ( $wiki === false ) {
-				$conn = $this->getAnyOpenConnection( $i );
-			}
-			if ( !$conn ) {
-				$conn = $this->openConnection( $i, $wiki );
-			}
-			if ( !$conn ) {
-				continue;
-			}
-			$lag = $conn->getLag();
-			if ( $lag > $maxLag ) {
-				$maxLag = $lag;
-				$host = $this->mServers[$i]['host'];
-				$maxIndex = $i;
+		if ( $this->getServerCount() > 1 ) { // no replication = no lag
+			foreach ( $this->mServers as $i => $conn ) {
+				$conn = false;
+				if ( $wiki === false ) {
+					$conn = $this->getAnyOpenConnection( $i );
+				}
+				if ( !$conn ) {
+					$conn = $this->openConnection( $i, $wiki );
+				}
+				if ( !$conn ) {
+					continue;
+				}
+				$lag = $conn->getLag();
+				if ( $lag > $maxLag ) {
+					$maxLag = $lag;
+					$host = $this->mServers[$i]['host'];
+					$maxIndex = $i;
+				}
 			}
 		}
 		return array( $host, $maxLag, $maxIndex );
@@ -972,8 +976,14 @@ class LoadBalancer {
 		if ( isset( $this->mLagTimes ) ) {
 			return $this->mLagTimes;
 		}
-		# No, send the request to the load monitor
-		$this->mLagTimes = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
+		if ( $this->getServerCount() == 1 ) {
+			# No replication
+			$this->mLagTimes = array( 0 => 0 );
+		} else {
+			# Send the request to the load monitor
+			$this->mLagTimes = $this->getLoadMonitor()->getLagTimes( 
+				array_keys( $this->mServers ), $wiki );
+		}
 		return $this->mLagTimes;
 	}
 
diff --git a/includes/db/LoadMonitor.php b/includes/db/LoadMonitor.php
index 226036ad9a..a6370c9e03 100644
--- a/includes/db/LoadMonitor.php
+++ b/includes/db/LoadMonitor.php
@@ -106,6 +106,11 @@ class LoadMonitor_MySQL implements LoadMonitor {
 	 * @return array
 	 */
 	function getLagTimes( $serverIndexes, $wiki ) {
+		if ( count( $serverIndexes ) == 1 && reset( $serverIndexes ) == 0 ) {
+			// Single server only, just return zero without caching
+			return array( 0 => 0 );
+		}
+
 		wfProfileIn( __METHOD__ );
 		$expiry = 5;
 		$requestRate = 10;