When MySQL is using repeatable-read transaction isolation (which is the
default), the following sequence of events can occur:
1. Request A: Begin a transaction.
2. Request A: Try to select the actor ID for a user. Find no rows.
3. Request B: Insert an actor ID for that user.
4. Request A: Try to insert an actor ID for the user. Fails because one
exists.
5. Request A: Try to select the actor ID that must exist. Fail because of
the snapshot created at step 2.
In MySQL we can avoid this issue at step #5 by using a locking select
(FOR UPDATE or LOCK IN SHARE MODE), so let's do that.
Bug: T210621
Change-Id: I6c1d255fdd14c6f49d2ea9790e7bd7d101e98ee4
(cherry picked from commit
37f48fdb25a78ba7623c57b50cdfd842292d3ccb)
if --lang is used with the command-line installer (install.php).
* Fix addition of ug_expiry column to user_groups table on MSSQL.
* (T204767) Add join conditions to ActiveUsersPager
+* (T210621) User: Bypass repeatable-read when creating an actor_id.
== MediaWiki 1.31.1 ==
$this->mActorId = (int)$dbw->insertId();
} else {
// Outdated cache?
- list( , $options ) = DBAccessObjectUtils::getDBOptions( $this->queryFlagsUsed );
- $this->mActorId = (int)$dbw->selectField( 'actor', 'actor_id', $q, __METHOD__, $options );
+ // Use LOCK IN SHARE MODE to bypass any MySQL REPEATABLE-READ snapshot.
+ $this->mActorId = (int)$dbw->selectField(
+ 'actor',
+ 'actor_id',
+ $q,
+ __METHOD__,
+ [ 'LOCK IN SHARE MODE' ]
+ );
if ( !$this->mActorId ) {
throw new CannotCreateActorException(
"Cannot create actor ID for user_id={$this->getId()} user_name={$this->getName()}"