Bug #119159 Some data is not rolled back successfully

• Submitted: 15 Oct 2025 9:23
• Reporter: Kate Green
• Status: Open
• Category: MySQL Server: InnoDB storage engine
• Severity: S2 (Serious)
• Version: 9.4.0
• OS: Any
• CPU Architecture: Any
• Tags: read uncommitted, rollback, transaction

[15 Oct 2025 9:23] Kate Green

Description:
Isolation level: READ UNCOMMITTED
If the following four transactions are executed concurrently, some data is not successfully rolled back.

How to repeat:
/* init */ CREATE TABLE t (c1 TINYTEXT);
/* init */ INSERT INTO t VALUES ('aa');
/* init */ INSERT INTO t VALUES ('bb');
/* init */ INSERT INTO t VALUES ('cc');
/* init */ INSERT INTO t VALUES ('aa');
/* init */ INSERT INTO t VALUES ('bb');
/* init */ INSERT INTO t VALUES ('cc');

There are two sessions session1 and session2 executing concurrently.

Session1 executes transactions t1 and t3 successively.
/* t1 */
BEGIN;
UPDATE IGNORE t SET c1 = 'dd';
ROLLBACK;

/* t3 */
START TRANSACTION;
UPDATE LOW_PRIORITY IGNORE t SET c1 = 'ee';
INSERT INTO t VALUES ('ff');
INSERT LOW_PRIORITY IGNORE INTO t VALUES ('gg');
ROLLBACK;

Session2 executes transactions t2 and t4 successively.
/* t2 */
BEGIN;
SELECT ta1.c1 AS ca1 FROM t JOIN t AS ta1;
DELETE FROM t;
ROLLBACK;

/* t4 */
BEGIN;
REPLACE INTO t VALUES ('hh');
SELECT c1 FROM t;
SELECT c1 FROM t; -- [('ee'), ('ee'), ('cc'), ('aa'), ('bb'), ('cc'), ('hh')]
COMMIT;

In the query results of the 4th statement in transaction t4, rows 3-6 are the values ​​after transaction t3 is rolled back (i.e., the values ​​in the initial database), and rows 1-2 are the values ​​before transaction t3 is rolled back (i.e., the values ​​updated by the 2nd statement in t3).