From de0b371aac3904e28c830a6796512bb46e560e30 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Fri, 2 Sep 2016 11:06:56 -0700
Subject: [PATCH] Add flushReplicaSnapshots() method for just clearing
 snapshots

This is better than having to use the less safe commitAll(),
which also checks and commits masters with writes.

Change-Id: I01c95f1ebae6927ed5acf0c23dd19b5c2413f661
---
 includes/db/loadbalancer/LBFactory.php    | 10 +++++++
 includes/db/loadbalancer/LoadBalancer.php | 32 +++++++++++++++++++++++
 includes/jobqueue/JobRunner.php           |  2 +-
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/includes/db/loadbalancer/LBFactory.php b/includes/db/loadbalancer/LBFactory.php
index 2e6f602ce5..6b5161b0b1 100644
--- a/includes/db/loadbalancer/LBFactory.php
+++ b/includes/db/loadbalancer/LBFactory.php
@@ -248,6 +248,16 @@ abstract class LBFactory implements DestructibleService {
 		$this->forEachLBCallMethod( 'beginMasterChanges', [ $fname ] );
 	}
 
+	/**
+	 * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
+	 *
+	 * @param string $fname Caller name
+	 * @since 1.28
+	 */
+	public function flushReplicaSnapshots( $fname = __METHOD__ ) {
+		$this->forEachLBCallMethod( 'flushReplicaSnapshots', [ $fname ] );
+	}
+
 	/**
 	 * Commit on all connections. Done for two reasons:
 	 * 1. To commit changes to the masters.
diff --git a/includes/db/loadbalancer/LoadBalancer.php b/includes/db/loadbalancer/LoadBalancer.php
index c554f17109..41e3631520 100644
--- a/includes/db/loadbalancer/LoadBalancer.php
+++ b/includes/db/loadbalancer/LoadBalancer.php
@@ -1317,6 +1317,18 @@ class LoadBalancer {
 		}
 	}
 
+	/**
+	 * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
+	 *
+	 * @param string $fname Caller name
+	 * @since 1.28
+	 */
+	public function flushReplicaSnapshots( $fname = __METHOD__ ) {
+		$this->forEachOpenReplicaConnection( function ( DatabaseBase $conn ) {
+			$conn->clearSnapshot( __METHOD__ );
+		} );
+	}
+
 	/**
 	 * @return bool Whether a master connection is already open
 	 * @since 1.24
@@ -1559,6 +1571,26 @@ class LoadBalancer {
 		}
 	}
 
+	/**
+	 * Call a function with each open replica DB connection object
+	 * @param callable $callback
+	 * @param array $params
+	 * @since 1.28
+	 */
+	public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
+		foreach ( $this->mConns as $connsByServer ) {
+			foreach ( $connsByServer as $i => $serverConns ) {
+				if ( $i === $this->getWriterIndex() ) {
+					continue; // skip master
+				}
+				foreach ( $serverConns as $conn ) {
+					$mergedParams = array_merge( [ $conn ], $params );
+					call_user_func_array( $callback, $mergedParams );
+				}
+			}
+		}
+	}
+
 	/**
 	 * Get the hostname and lag time of the most-lagged slave
 	 *
diff --git a/includes/jobqueue/JobRunner.php b/includes/jobqueue/JobRunner.php
index f25c1ba5c5..112696b5e3 100644
--- a/includes/jobqueue/JobRunner.php
+++ b/includes/jobqueue/JobRunner.php
@@ -289,7 +289,7 @@ class JobRunner implements LoggerAwareInterface {
 		// Commit all outstanding connections that are in a transaction
 		// to get a fresh repeatable read snapshot on every connection.
 		// Note that jobs are still responsible for handling slave lag.
-		$lbFactory->commitAll( __METHOD__ );
+		$lbFactory->flushReplicaSnapshots( __METHOD__ );
 		// Clear out title cache data from prior snapshots
 		LinkCache::singleton()->clear();
 		$timeMs = intval( ( microtime( true ) - $jobStartTime ) * 1000 );
-- 
2.20.1