maria-discuss team mailing list archive

[andrei.elkin@xxxxxxxxxx]

Kristian,

> andrei.elkin@xxxxxxxxxx writes:
>
>> Mike,
>>
>>> Hello,
>>>
>>> I realize that in general replication from a newer master to an older
>>> slave is typically not recommended.  This said, does anyone have an
>>> experience replicating from MariaDB 10.2 to MySQL 5.6?
>>
>> A problem that is evident at once is 10.2 GTID events can not be handled
>> by 5.6. So at least some filtering should be devised.
>
> 10.2 does not send GTID to a slave that does not understand it (they are
> rewritten on-the-fly to BEGIN query events). So GTID events should not cause
> 5.6 slave to break.

Thanks for correcting! The gtid filtering meant is therefore already
in the server :-).

>
> More generally, the code in MariaDB (at least the code that I wrote) detects
> what capabilities the slave has, and avoids sending stuff from the master
> that an old slave will not understand. See MARIA_SLAVE_CAPABILITY_* in
> log_event.h.
>
> So the intention is that replication to old slave should work. However, this
> still requires that applications restrict themselves from using any SQL not
> supported on the old slave. And it is only poorly tested, if at all. Hence
> the recommendation to avoid new master->old slave.

To detail on that for the statement-based replication the old slave may ignore a part of
execution context that the new master records into events, typically
into Query-log-event. While ignorance is bliss it can lead to
inconsistency in this case.

Cheers,

Andrei