From: Brad Jorsch <bjorsch@wikimedia.org>
Date: Tue, 2 Apr 2019 14:07:56 +0000 (-0400)
Subject: MigrateActors: Improve query for log_search rows
X-Git-Tag: 1.34.0-rc.0~2187^2
X-Git-Url: https://git.cyclocoop.org/%7B%24admin_url%7Dmembres/cotisations/rappels.php?a=commitdiff_plain;h=42b14d98b5dca07c8180468bbc02fccea2721e62;p=lhc%2Fweb%2Fwiklou.git

MigrateActors: Improve query for log_search rows

The query in question is, generically,

 SELECT ls_value, ls_log_id, actor_id
  FROM log_search LEFT JOIN actor ON (ls_value = actor_user)
  WHERE ls_field = 'target_author_id'
  ORDER BY ls_value, ls_log_id
  LIMIT 100;

The intention is that it'll pull out 100 rows from log_search using its
primary key, and for each of those 100 rows find the actor_id for the
referenced user_id (using the actor_user index) if an actor ID exists.

The twist comes in the fact that ls_value is a string-type column while
actor_user is an integer-type. MySQL doesn't usually care, but other DBs
do so we have to cast one into the other.

Currently the code is casting actor_user to a string. But that means the
DB can't use the index on actor_user to find the one matching row,
instead it needs to scan the whole table.

The fix is simple enough: instead of casting actor_user to a string,
cast ls_value to an integer. That allows the actor_user index to be used
as expected.

Bug: T215525
Change-Id: I2f7a6ba9fd537336594088a0281a62ea5601cd59
---

diff --git a/maintenance/includes/MigrateActors.php b/maintenance/includes/MigrateActors.php
index f5b366690c..aff67587b4 100644
--- a/maintenance/includes/MigrateActors.php
+++ b/maintenance/includes/MigrateActors.php
@@ -504,7 +504,7 @@ class MigrateActors extends LoggedUpdateMaintenance {
 					'ORDER BY' => $primaryKey,
 					'LIMIT' => $this->mBatchSize,
 				],
-				[ 'actor' => [ 'LEFT JOIN', 'ls_value = ' . $dbw->buildStringCast( 'actor_user' ) ] ]
+				[ 'actor' => [ 'LEFT JOIN', 'actor_user = ' . $dbw->buildIntegerCast( 'ls_value' ) ] ]
 			);
 			if ( !$res->numRows() ) {
 				break;