Merge "Log to DBPerformance log when many LB connections are acquired"

[lhc/web/wiklou.git] / includes / db / LoadMonitor.php

diff --git a/includes/db/LoadMonitor.php b/includes/db/LoadMonitor.php
index fa2dd99..91840dd 100644 (file)
--- a/includes/db/LoadMonitor.php
+++ b/includes/db/LoadMonitor.php
@@ -48,7 +48,7 @@ interface LoadMonitor {
         * @param array $serverIndexes
         * @param string $wiki
         *
-        * @return array
+        * @return array Map of (server index => seconds)
         */
        public function getLagTimes( $serverIndexes, $wiki );
 }
@@ -74,9 +74,14 @@ class LoadMonitorNull implements LoadMonitor {
 class LoadMonitorMySQL implements LoadMonitor {
        /** @var LoadBalancer */
        public $parent;
+       /** @var BagOStuff */
+       protected $cache;
 
        public function __construct( $parent ) {
+               global $wgMemc;
+
                $this->parent = $parent;
+               $this->cache = $wgMemc ?: wfGetMainCache();
        }
 
        public function scaleLoads( &$loads, $group = false, $wiki = false ) {
@@ -88,19 +93,13 @@ class LoadMonitorMySQL implements LoadMonitor {
                        return array( 0 => 0 );
                }
 
-               $section = new ProfileSection( __METHOD__ );
-
                $expiry = 5;
                $requestRate = 10;
 
-               global $wgMemc;
-               if ( empty( $wgMemc ) ) {
-                       $wgMemc = wfGetMainCache();
-               }
-
+               $cache = $this->cache;
                $masterName = $this->parent->getServerName( 0 );
                $memcKey = wfMemcKey( 'lag_times', $masterName );
-               $times = $wgMemc->get( $memcKey );
+               $times = $cache->get( $memcKey );
                if ( is_array( $times ) ) {
                        # Randomly recache with probability rising over $expiry
                        $elapsed = time() - $times['timestamp'];
@@ -116,10 +115,10 @@ class LoadMonitorMySQL implements LoadMonitor {
                }
 
                # Cache key missing or expired
-               if ( $wgMemc->add( "$memcKey:lock", 1, 10 ) ) {
+               if ( $cache->add( "$memcKey:lock", 1, 10 ) ) {
                        # Let this process alone update the cache value
-                       $unlocker = new ScopedCallback( function () use ( $wgMemc, $memcKey ) {
-                               $wgMemc->delete( $memcKey );
+                       $unlocker = new ScopedCallback( function () use ( $cache, $memcKey ) {
+                               $cache->delete( $memcKey );
                        } );
                } elseif ( is_array( $times ) ) {
                        # Could not acquire lock but an old cache exists, so use it
@@ -136,12 +135,17 @@ class LoadMonitorMySQL implements LoadMonitor {
                                $times[$i] = $conn->getLag();
                        } elseif ( false !== ( $conn = $this->parent->openConnection( $i, $wiki ) ) ) {
                                $times[$i] = $conn->getLag();
+                               // Close the connection to avoid sleeper connections piling up.
+                               // Note that the caller will pick one of these DBs and reconnect,
+                               // which is slightly inefficient, but this only matters for the lag
+                               // time cache miss cache, which is far less common that cache hits.
+                               $this->parent->closeConnection( $conn );
                        }
                }
 
                # Add a timestamp key so we know when it was cached
                $times['timestamp'] = time();
-               $wgMemc->set( $memcKey, $times, $expiry + 10 );
+               $cache->set( $memcKey, $times, $expiry + 10 );
                unset( $times['timestamp'] ); // hide from caller
 
                return $times;