Re: [HACKERS] Quorum commit for multiple synchronous replication.

On Thu, Dec 15, 2016 at 3:06 PM, Kyotaro HORIGUCHI
<horiguchi.kyotaro@lab.ntt.co.jp> wrote:
> At Thu, 15 Dec 2016 14:20:53 +0900, Masahiko Sawada <sawada.mshk@gmail.com> wrote in
<CAD21AoDn73aC+o0mrWCs800LeOsMYP4oV7xVb0T0_4V5VCQzhQ@mail.gmail.com>
>> On Thu, Dec 15, 2016 at 11:23 AM, Michael Paquier
>> <michael.paquier@gmail.com> wrote:
>> > On Thu, Dec 15, 2016 at 11:04 AM, Fujii Masao <masao.fujii@gmail.com> wrote:
>> >> On Thu, Dec 15, 2016 at 6:47 AM, Michael Paquier
>> >> <michael.paquier@gmail.com> wrote:
>> >>> On Wed, Dec 14, 2016 at 11:34 PM, Fujii Masao <masao.fujii@gmail.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.
>
> FWIW, +1 from me.
>
>> I'll update the patch.
>

Attached latest v12 patch.
I changed behavior of "N (standby_list)" to use the priority method
and incorporated some review comments so far. Please review it.

Regards,

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

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