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 b3f9210..7e9c08c 100644 (file)
--- 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 0009999..633b34a 100644 (file)
--- 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." );
                }