From e0c286646ec5bcd5599d487cc7725ba4053d2939 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Sat, 20 Dec 2014 03:58:35 -0800
Subject: [PATCH] Log to DBPerformance log when many LB connections are
 acquired

Change-Id: Idcb7233bc418a793b87f4d445807be5eced12d95
---
 includes/db/LoadBalancer.php | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/includes/db/LoadBalancer.php b/includes/db/LoadBalancer.php
index f789d56ac1..f11ef0cd36 100644
--- a/includes/db/LoadBalancer.php
+++ b/includes/db/LoadBalancer.php
@@ -58,9 +58,14 @@ class LoadBalancer {
 	private $mLaggedSlaveMode;
 	/** @var string The last DB selection or connection error */
 	private $mLastError = 'Unknown error';
+	/** @var integer Total connections opened */
+	private $connsOpened = 0;
 	/** @var ProcessCacheLRU */
 	private $mProcCache;
 
+	/** @var integer Warn when this many connection are held */
+	const CONN_HELD_WARN_THRESHOLD = 10;
+
 	/**
 	 * @param array $params Array with keys:
 	 *   servers           Required. Array of server info structures.
@@ -735,6 +740,14 @@ class LoadBalancer {
 			$server['dbname'] = $dbNameOverride;
 		}
 
+		// Log when many connection are made on requests
+		if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
+			$masterAddr = $this->getServerName( 0 );
+			wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
+				"{$this->connsOpened}+ connections made (master=$masterAddr)\n" .
+				wfBacktrace( true ) );
+		}
+
 		# Create object
 		try {
 			$db = DatabaseBase::factory( $server['type'], $server );
@@ -906,6 +919,7 @@ class LoadBalancer {
 			'foreignFree' => array(),
 			'foreignUsed' => array(),
 		);
+		$this->connsOpened = 0;
 	}
 
 	/**
@@ -922,6 +936,7 @@ class LoadBalancer {
 					if ( $conn === $candidateConn ) {
 						$conn->close();
 						unset( $this->mConns[$i1][$i2][$i3] );
+						--$this->connsOpened;
 						$done = true;
 						break;
 					}
-- 
2.20.1