Re: Quorum commit for multiple synchronous replication.

On Thu, Dec 15, 2016 at 11:23 AM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> On Thu, Dec 15, 2016 at 11:04 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>> On Thu, Dec 15, 2016 at 6:47 AM, Michael Paquier
>> <michael(dot)paquier(at)gmail(dot)com> wrote:
>>> On Wed, Dec 14, 2016 at 11:34 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>>>> If we drop the "standby_list" syntax, I don't think that new parameter is
>>>> necessary. We can keep s_s_names and just drop the support for that syntax
>>>> from s_s_names. This may be ok if we're really in "break all the things" mode
>>>> for PostgreSQL 10.
>>>
>>> Please let's not raise that as an argument again... And not break the
>>> s_list argument. Many users depend on that for just single sync
>>> standbys. FWIW, I'd be in favor of backward compatibility and say that
>>> a standby list is a priority list if we can maintain that. Upthread
>>> agreement was to break that, I did not insist further, and won't if
>>> that's still the feeling.
>>
>> I wonder why you think that the backward-compatibility for standby_list is
>> so "special". We renamed pg_xlog directory to pg_wal and are planning to
>> change recovery.conf API at all, though they have bigger impacts on
>> the existing users in terms of the backward compatibility. OTOH, so far,
>> changing GUC between major releases happened several times.
>
> Silent failures for existing failover deployments is a pain to solve
> after doing upgrades. That's my only concern. Changing pg_wal would
> result in a hard failure when upgrading. And changing the meaning of
> the standby list (without keyword ANY or FIRST!) does not fall into
> that category... So yes just removing support for standby list would
> result in a hard failure, which would be fine for the
> let-s-break-all-things move.
>
>> But I'm not against keeping the backward compatibility for standby_list,
>> to be honest. My concern is that the latest patch tries to support
>> the backward compatibility "partially" and which would be confusing to users,
>> as I told upthread.
> If we try to support backward compatibility, I'd personally do it
> fully, and have a list of standby names specified meaning a priority
> list.
>
>> So I'd like to propose to keep the backward compatibility fully for s_s_names
>> (i.e., both "standby_list" and "N (standby_list)" mean the priority method)
>> at the first commit, then continue discussing this and change it if we reach
>> the consensus until PostgreSQL 10 is actually released. Thought?
>
> +1 on that.

+1.
I'll update the patch.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center