From 922e68f739f143ad13c02abe56cc92f797f60081 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Wed, 5 Apr 2017 17:25:45 -0700
Subject: [PATCH] Reduce contention during view-based category count refreshes

Bug: T162121
Change-Id: I05b539922508d5e73979ccc8ea1c148b16dd13db
---
 includes/CategoryViewer.php | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/includes/CategoryViewer.php b/includes/CategoryViewer.php
index 31369b0187..0205d708ca 100644
--- a/includes/CategoryViewer.php
+++ b/includes/CategoryViewer.php
@@ -742,7 +742,13 @@ class CategoryViewer extends ContextSource {
 			$totalcnt = $rescnt;
 			$category = $this->cat;
 			DeferredUpdates::addCallableUpdate( function () use ( $category ) {
-				$category->refreshCounts();
+				# Avoid excess contention on the same category (T162121)
+				$dbw = wfGetDB( DB_MASTER );
+				$name = __METHOD__ . ':' . md5( $this->mName );
+				$scopedLock = $dbw->getScopedLockAndFlush( $name, __METHOD__, 1 );
+				if ( $scopedLock ) {
+					$category->refreshCounts();
+				}
 			} );
 		} else {
 			// Case 3: hopeless.  Don't give a total count at all.
-- 
2.20.1