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Re: Pacemaker and mariadb semi-sync


Note also that you don't want to set rpl_semi_sync_master_enabled='ON'
on all your slaves, it should be set only on the master. With the
setting your slaves' SQL threads will hang waiting for semi-sync ack
as well, and they will hang forever if
rpl_semi_sync_master_wait_no_slave is set to ON too.

On Wed, Aug 9, 2017 at 2:30 AM, Kristian Nielsen
<knielsen@xxxxxxxxxxxxxxx> wrote:
> Nils Carlson <pyssling@xxxxxxxxxxx> writes:
>> I would be very happy for some review (and even testing) of this
>> resource-agent from somebody with expertise in mariadb replication.
> I do not think I can offer review or testing, but I can give a few general
> remarks, maybe they can be helpful.
>> The parameter set on each node is as follows:
>> SET GLOBAL rpl_semi_sync_slave_enabled='ON', \
>>                            rpl_semi_sync_master_enabled='ON', \
>>                            rpl_semi_sync_master_wait_point='AFTER_SYNC',
>> \
>>                            gtid_strict_mode='ON', \
>>                            sync_binlog=1, \
>>                            sync_master_info=1, \
>>                            sync_relay_log=1, \
>>                            sync_relay_log_info=1;
>> I suspect this may be overkill, but I don't have the competence to
>> judge.
> gtid_strict_mode='ON' is good.
> I assume that the slaves are also set up with MASTER_USE_GTID=slave_pos (or
> current_pos).
> sync_relay_log=1 and sync_relay_log_info=1 would be quite bad for
> performance on a busy server. And they do not really make things any safer,
> in my opinion. The GTID position is stored transactionally in a table
> (assuming InnoDB storage engine), not in relay_log.info, and the relay log
> is in any case deleted and reloaded from the new master.
> On the other hand, innodb_flush_log_at_trx_commit=1 is needed (together with
> sync_binlog=1) to ensure transactional consistency between (InnoDB) data and
> binlog.
>> The general idea is to select the master at startup and failure as the
>> node with the highest GTID.
> This should work fine in the simple cases with a single domain ID used and
> no multi-source replication.
> In more complex cases, it is possible for one node to be ahead in on
> replication domain, while another node is ahead in another, so that no
> single node has the "highest GTID". The way to handle this is described
> here:
>   https://mariadb.com/kb/en/mariadb/gtid/#start-slave-until-master_gtid_posxxx
> I think it is perfectly fine to start with the simple approach you describe.
> That should be by far the most common use case. Just good to be aware about
> the general case.
> Hope this helps,
>  - Kristian.
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