Possible race condition leading to concurrent requests being executed in a
different order on backends
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Key: SEQUOIA-1034
URL: https://forge.continuent.org/jira/browse/SEQUOIA-1034
Project: Sequoia
Type: Bug
Components: Core
Versions: Sequoia 2.10.9
Reporter: Stephane Giron
Assigned to: Stephane Giron
Priority: Critical
Fix For: sequoia 2.10.10
This can lead to backends inconsistencies.
As an example, this is the behavior that was observed :
CREATE TABLE `table1` (
`db_id` bigint(20) NOT NULL auto_increment,
`col1` varchar(255) default NULL,
`creation_date` datetime default NULL,
`request_date` varchar(255) default NULL,
`col2` varchar(255) default NULL,
`version` varchar(255) default NULL,
PRIMARY KEY (`db_id`),
UNIQUE KEY `col1` (`col1`,`col2`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
Transaction 1
begin
insert into table1 (version) values('a1');
insert into table1 (version) values('c1');
commit
Transaction 2
begin
insert into table1 (version) values('b')
commit
T1 begin
T2 begin
T1 insert 1
T2 insert 1
T1 insert 2
commits
The following result is what I got in the backends :
On one controller :
| 8 | NULL | NULL | NULL | NULL | a1 |
| 9 | NULL | NULL | NULL | NULL | c1 |
| 10 | NULL | NULL | NULL | NULL | b |
On the other :
| 8 | NULL | NULL | NULL | NULL | a1 |
| 9 | NULL | NULL | NULL | NULL | b |
| 10 | NULL | NULL | NULL | NULL | c1 |
This can happen if the statement "T2 insert 1", which will be posted in the
conflicting queue, can be processed on one controller (because there is nothing
else at this time in the non conflicting queue), whereas on the other
controller the "T1 insert 2" statement arrives in the non conflicting queue
before "T2 insert 1" starts executing.
This behavior can be observed essentially because of the auto incremented key.
However other type of statements may run out of order as well.
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