From: Brad Jorsch <bjorsch@wikimedia.org>
Date: Tue, 16 Apr 2019 17:45:32 +0000 (-0400)
Subject: Add STRAIGHT_JOIN to ApiQueryLogEvents and LogPager to avoid planner oddness
X-Git-Tag: 1.34.0-rc.0~1871^2
X-Git-Url: https://git.heureux-cyclage.org/?p=lhc%2Fweb%2Fwiklou.git;a=commitdiff_plain;h=3d1fb0c0443ee92531ca8e1aafbcf9b403879e44

Add STRAIGHT_JOIN to ApiQueryLogEvents and LogPager to avoid planner oddness

For some unknown reason, when the `actor` table has few enough rows (or
few enough compared to `logging`) MariaDB 10.1.37 decides it makes more
sense to fetch everything from `actor` + `logging` and filesort rather than
fetching the limited number of rows from `logging`.

We can work around it by telling it to not reorder the query.

Bug: T220999
Bug: T221458
Change-Id: I9da981c09f18ba72efeeb8279aad99eb21af699a
---

diff --git a/includes/api/ApiQueryLogEvents.php b/includes/api/ApiQueryLogEvents.php
index 779868845a..962d956130 100644
--- a/includes/api/ApiQueryLogEvents.php
+++ b/includes/api/ApiQueryLogEvents.php
@@ -238,6 +238,14 @@ class ApiQueryLogEvents extends ApiQueryBase {
 			}
 		}
 
+		// T220999: MySQL/MariaDB (10.1.37) can sometimes irrationally decide that querying `actor` before
+		// `logging` and filesorting is somehow better than querying $limit+1 rows from `logging`.
+		// Tell it not to reorder the query. But not when `letag` was used, as it seems as likely
+		// to be harmed as helped in that case.
+		if ( $params['tag'] === null ) {
+			$this->addOption( 'STRAIGHT_JOIN' );
+		}
+
 		$count = 0;
 		$res = $this->select( __METHOD__ );
 		$result = $this->getResult();
diff --git a/includes/logging/LogPager.php b/includes/logging/LogPager.php
index 801c4745c9..0eeb544eb3 100644
--- a/includes/logging/LogPager.php
+++ b/includes/logging/LogPager.php
@@ -335,6 +335,14 @@ class LogPager extends ReverseChronologicalPager {
 		# Don't show duplicate rows when using log_search
 		$joins['log_search'] = [ 'JOIN', 'ls_log_id=log_id' ];
 
+		// T221458: MySQL/MariaDB (10.1.37) can sometimes irrationally decide that querying `actor` before
+		// `logging` and filesorting is somehow better than querying $limit+1 rows from `logging`.
+		// Tell it not to reorder the query. But not when tag filtering was used, as it seems as likely
+		// to be harmed as helped in that case.
+		if ( !$this->mTagFilter ) {
+			$options[] = 'STRAIGHT_JOIN';
+		}
+
 		$info = [
 			'tables' => $tables,
 			'fields' => $fields,