From: Aaron Schulz <aschulz@wikimedia.org>
Date: Sat, 20 Feb 2016 00:14:58 +0000 (-0800)
Subject: Ignore noop DB transactions errors on connection loss
X-Git-Tag: 1.31.0-rc.0~7822^2
X-Git-Url: http://git.cyclocoop.org/%24action?a=commitdiff_plain;h=38f0c072799a298929a922b615c2ba1883c6067b;p=lhc%2Fweb%2Fwiklou.git

Ignore noop DB transactions errors on connection loss

This avoids some needless exceptions for longer running scripts.

Bug: T127428
Change-Id: I3098141aa77a4c73cb2a0c784b38b15c712f82a9
---

diff --git a/includes/db/Database.php b/includes/db/Database.php
index 351d43845a..02a6ec870b 100644
--- a/includes/db/Database.php
+++ b/includes/db/Database.php
@@ -859,8 +859,12 @@ abstract class DatabaseBase implements IDatabase {
 
 		# Try reconnecting if the connection was lost
 		if ( false === $ret && $this->wasErrorReissuable() ) {
-			# Transaction is gone, like it or not
-			$hadTrx = $this->mTrxLevel; // possible lost transaction
+			# Transaction is gone; this can mean lost writes or REPEATABLE-READ snapshots
+			$hadTrx = $this->mTrxLevel;
+			# T127428: for non-write transactions, a disconnect and a COMMIT are similar:
+			# neither changed data and in both cases any read snapshots are reset anyway.
+			$isNoopCommit = ( !$this->writesOrCallbacksPending() && $sql === 'COMMIT' );
+			# Update state tracking to reflect transaction loss
 			$this->mTrxLevel = 0;
 			$this->mTrxIdleCallbacks = []; // bug 65263
 			$this->mTrxPreCommitCallbacks = []; // bug 65263
@@ -874,12 +878,12 @@ abstract class DatabaseBase implements IDatabase {
 				$msg = __METHOD__ . ": lost connection to $server; reconnected";
 				wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 
-				if ( $hadTrx || $this->mNamedLocksHeld ) {
+				if ( ( $hadTrx && !$isNoopCommit ) || $this->mNamedLocksHeld ) {
 					# Leave $ret as false and let an error be reported.
 					# Callers may catch the exception and continue to use the DB.
 					$this->reportQueryError( $lastError, $lastErrno, $sql, $fname, $tempIgnore );
 				} else {
-					# Should be safe to silently retry (no trx and thus no callbacks)
+					# Should be safe to silently retry (no trx/callbacks/locks)
 					$startTime = microtime( true );
 					$ret = $this->doQuery( $commentedSql );
 					$queryRuntime = microtime( true ) - $startTime;