From: Aaron Schulz <aschulz@wikimedia.org>
Date: Thu, 10 Jul 2014 17:46:42 +0000 (-0700)
Subject: Made getMaxLag() use caching to reduce connection spam
X-Git-Tag: 1.31.0-rc.0~14993^2
X-Git-Url: https://git.cyclocoop.org//%22?a=commitdiff_plain;h=f9ddcb04539398dc7432aacd456e1ba9ed0b64a6;p=lhc%2Fweb%2Fwiklou.git

Made getMaxLag() use caching to reduce connection spam

* This method is currently hit when bots use the maxlag API parameter
* Also added a $fallback param to ObjectCache::newAccelerator so code
  does not have to keep reinventing that logic.

Change-Id: I45bf1085301c5cf69b29b494a146c6a067534581
---

diff --git a/includes/db/LoadBalancer.php b/includes/db/LoadBalancer.php
index b3f9210120..7e9c08cd69 100644
--- a/includes/db/LoadBalancer.php
+++ b/includes/db/LoadBalancer.php
@@ -1048,7 +1048,18 @@ class LoadBalancer {
 		$maxLag = -1;
 		$host = '';
 		$maxIndex = 0;
-		if ( $this->getServerCount() > 1 ) { // no replication = no lag
+
+		if ( $this->getServerCount() <= 1 ) { // no replication = no lag
+			return array( $host, $maxLag, $maxIndex );
+		}
+
+		// Try to get the max lag info from the server cache
+		$key = 'loadbalancer:maxlag:cluster:' . $this->mServers[0]['host'];
+		$cache = ObjectCache::newAccelerator( array(), 'hash' );
+		$maxLagInfo = $cache->get( $key ); // (host, lag, index)
+
+		// Fallback to connecting to each slave and getting the lag
+		if ( !$maxLagInfo ) {
 			foreach ( $this->mServers as $i => $conn ) {
 				$conn = false;
 				if ( $wiki === false ) {
@@ -1067,9 +1078,11 @@ class LoadBalancer {
 					$maxIndex = $i;
 				}
 			}
+			$maxLagInfo = array( $host, $maxLag, $maxIndex );
+			$cache->set( $key, $maxLagInfo, 5 );
 		}
 
-		return array( $host, $maxLag, $maxIndex );
+		return $maxLagInfo;
 	}
 
 	/**
diff --git a/includes/objectcache/ObjectCache.php b/includes/objectcache/ObjectCache.php
index 0009999aed..633b34a2c9 100644
--- a/includes/objectcache/ObjectCache.php
+++ b/includes/objectcache/ObjectCache.php
@@ -119,11 +119,15 @@ class ObjectCache {
 	/**
 	 * Factory function referenced from DefaultSettings.php for CACHE_ACCEL.
 	 *
+	 * This will look for any APC style server-local cache.
+	 * A fallback cache can be specified if none is found.
+	 *
 	 * @param array $params
+	 * @param int|string $fallback Fallback cache, e.g. (CACHE_NONE, "hash") (since 1.24)
 	 * @throws MWException
 	 * @return BagOStuff
 	 */
-	static function newAccelerator( $params ) {
+	static function newAccelerator( $params, $fallback = null ) {
 		if ( function_exists( 'apc_fetch' ) ) {
 			$id = 'apc';
 		} elseif ( function_exists( 'xcache_get' ) && wfIniGetBool( 'xcache.var_size' ) ) {
@@ -131,6 +135,9 @@ class ObjectCache {
 		} elseif ( function_exists( 'wincache_ucache_get' ) ) {
 			$id = 'wincache';
 		} else {
+			if ( $fallback ) {
+				return self::newFromId( $fallback );
+			}
 			throw new MWException( "CACHE_ACCEL requested but no suitable object " .
 				"cache is present. You may want to install APC." );
 		}