Bug #73125 setting slave_parallel_workers=0 should not be allowed 'if there are still gaps'

• Submitted: 26 Jun 2014 15:35
• Modified: 16 Jul 2014 10:58
• Reporter: Kenny Gryp
• Status: Verified
• Category: MySQL Server: Replication
• Severity: S3 (Non-critical)
• Version: 5.6
• OS: Any
• CPU Architecture: Any

[26 Jun 2014 15:35] Kenny Gryp

Description:
The slave_parallel_workers can be set to 0 even if 
'START SLAVE UNTIL SQL_AFTER_MTS_GAPS;' is not run manually first.

I know that the documentation of START SLAVE UNTIL states that there could be gaps if you set slave_parallel_workers=0. (it's not mentioned in the slave_parallel_workers documentation).
- not mentioned at: http://dev.mysql.com/doc/refman/5.6/en/replication-options-slave.html#sysvar_slave_paralle...
- mentioned in: http://dev.mysql.com/doc/refman/5.6/en/start-slave.html

How to repeat:

But, I think it should not be allowed to set slave_parallel_workers=0 as long as 'there are gaps'.

[26 Jun 2014 15:35] Kenny Gryp

added version and changed title.

[16 Jul 2014 10:58] MySQL Verification Team

Thank you for the report.

I'm not sure whether it is intended behavior but observed that when I tried to execute blocking statement on slave for a table in one database(to block update and create some gap), then tried  SET @@GLOBAL.slave_parallel_workers = 0.. It didn't complain and allowed to change it.

mysql> show global variables where Variable_name like 'slave_par%' OR Variable_name like 'relay_log_recovery%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| relay_log_recovery     | ON    |
| slave_parallel_workers | 10    |
+------------------------+-------+
2 rows in set (0.00 sec)

mysql> SET @@GLOBAL.slave_parallel_workers = 0;
Query OK, 0 rows affected (0.00 sec)

mysql> show global variables where Variable_name like 'slave_par%' OR Variable_name like 'relay_log_recovery%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| relay_log_recovery     | ON    |
| slave_parallel_workers | 0     |
+------------------------+-------+
2 rows in set (0.00 sec)

Thanks,
Umesh