MySQL Bugs: #84955: log_slave_updates should be dynamic

Bug #84955	log_slave_updates should be dynamic
Submitted:	10 Feb 2017 19:10	Modified:	10 Feb 2017 21:29
Reporter:	Trey Raymond	Email Updates:
Status:	Duplicate	Impact on me:	None
Category:	MySQL Server: Replication	Severity:	S3 (Non-critical)
Version:	5.7.x	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
there's seemingly no reason that changes to log_slave_updates require a restart - binary logging, if enabled globally, can already be enabled/disable per thread (re sql_log_bin).  It should simply require that the sql thread[s] are stopped for the "set".
Would make moving hosts around in replication easier - we have gtid and msr and mts and all of these great replication features, but still have to bounce for this!

How to repeat:
https://dev.mysql.com/doc/refman/5.7/en/replication-options-binary-log.html#sysvar_log_sla...

mysql> set global log_slave_updates=on;
ERROR 1238 (HY000): Variable 'log_slave_updates' is a read only variable

Suggested fix:
allow the var to be dynamic, and set as long as the sql threads are not running.  when said sql threads start, they would log or not log based on the current setting.

Thank you for the bug report. Duplicate of https://bugs.mysql.com/bug.php?id=35611.