[MDEV-32813] read-only xa prepare may disappear upon server restart Created: 2023-11-15  Updated: 2023-11-15

Status: Open
Project: MariaDB Server
Component/s: Replication, Server
Affects Version/s: 10.6
Fix Version/s: None

Type: Bug Priority: Major
Reporter: Andrei Elkin Assignee: Unassigned
Resolution: Unresolved Votes: 0
Labels: None

Issue Links:
Relates
relates to MDEV-742 LP:803649 - Xa recovery failed on cli... Closed

 Description   

A prepared user xa that does not modify any engine data may get binlogged. E.g
from binlog_empty_xa_prepared.test:

XA START '3';
 
CREATE TEMPORARY TABLE tmp_1(c INT);
 
XA END '3';
 
XA PREPARE '3';

ends in binlog with 

| master-bin.000001 | 555 | Gtid              |         1 |         600 | XA START X'33',X'',1 GTID 0-1-2                                |
 
| master-bin.000001 | 600 | Query             |         1 |         685 | XA END X'33',X'',1                                             |
 
| master-bin.000001 | 685 | XA_prepare        |         1 |         722 | XA PREPARE X'33',X'',1

and stays recovered

 > xa recover;
 
+----------+--------------+--------------+------+
 
| formatID | gtrid_length | bqual_length | data |
 
+----------+--------------+--------------+------+
 
|        1 |            1 |            0 | 3    |
 
+----------+--------------+--------------+------+

while the server is alive.

It's gone after the server restart.
 
shutdown;
 
Query OK, 0 rows affected (0.00 sec)
 
 
 
18:16:32 [test]> xa recover;
 
ERROR 2006 (HY000): MySQL server has gone away
 
No connection. Trying to reconnect...
 
Connection id:    4
 
Current database: test
 
 
 
Empty set (0.03 sec)

An obvious resolution is to prevent logging the empty XA-prepare group.
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