Re: Behaviour of take over the synchronous replication

On Sat, Aug 24, 2013 at 3:14 AM, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
> On 08/23/2013 12:42 AM, Sawada Masahiko wrote:
>> in case (a), those priority is clear. So I think that re-taking over
>> is correct behaviour.
>> OHOT, in case (b), even if AAA and BBB are set same priority, AAA
>> server steals SYNC replication.
>> I think it is better that BBB server continue behaviour SYNC standby,
>> and AAA should become potential server.
>
> So, you're saying that:
>
> 1) synchronous_standby_names = '*'
>
> 2) replica 'BBB' is the current sync standby
>
> 3) replica 'AAA' comes online
>
> 4) replica 'AAA' grabs sync status
>
> ?
I'm sorry that you are confuse.
It means that

1) synchronous_standby_names = '*'

2) replica 'AAA' is the current sync standby

3) replica 'BBB' is the current async standby (potential sync standby)

4) replica 'AAA' fail. after that, replica 'BBB' is current sync standby.

5) replica 'AAA' comes online

6) replica 'AAA' grabs sync status

>
> If that's the case, I'm not really sure that's undesirable behavior.
> One could argue fairly persuasively that if you care about the
> precendence order of sync replicas, you shouldn't use '*'. And the rule
> of "if using *, the lowest-sorted replica name has sync" is actually a
> predictable, easy-to-understand rule.
>
> So if you want to make this a feature request, you'll need to come up
> with an argument as to why the current behavior is bad. Otherwise,
> you're just asking us to document it better (which is a good idea).
It is not depend on name of standby server. That is, The standby server,
which was connected to the master server during initial configration
replication, is top priority even if priority of two server are same.

User must remember that which standby server connected to master server at
first.
I think that this behavior confuse user.
so I think that we need to modify this behaviour or if '*' is used,
priority of server is not same (modifying manual is also good).

Regards,

-------
Sawada Masahiko