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Re: Sync Rep v19

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: Yeb Havinga <yebhavinga(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Sync Rep v19
Date: 2011-03-19 02:28:33
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Fri, Mar 18, 2011 at 10:25 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Mar 8, 2011 at 7:05 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>> * Smart shutdown
>> Smart shutdown should wait for all the waiting backends to be acked, and
>> should not cause them to forcibly exit. But this leads shutdown to get stuck
>> infinitely if there is no walsender at that time. To enable them to be acked
>> even in that situation, we need to change postmaster so that it accepts the
>> replication connection even during smart shutdown (until we reach
>> PM_SHUTDOWN_2 state). Postmaster has already accepted the superuser
>> connection to cancel backup during smart shutdown. So I don't think that
>> the idea to accept the replication connection during smart shutdown is so
>> ugly.
>> * Fast shutdown
>> I agree with you about fast shutdown. Fast shutdown should cause all the
>> backends including waiting ones to exit immediately. At that time, the
>> non-acked backend should not return the success, according to the
>> definition of sync rep. So we need to change a backend so that it gets rid
>> of itself from the waiting queue and exits before returning the success,
>> when it receives SIGTERM. This change leads the waiting backends to
>> do the same even when pg_terminate_backend is called. But since
>> they've not been acked yet, it seems to be reasonable to prevent them
>> from returning the COMMIT.
>> Comments? I'll create the patch barring objection.
> The fast smart shutdown part of this problem has been addressed.  The

Ugh.  I mean "the fast shutdown", of course, not "the fast smart
shutdown".  Anyway, point is:

fast shutdown now OK
smart shutdown still not OK
do you want to write a patch?


> smart shutdown case still needs work, and I think the consensus was
> that your proposal above was the best way to go with it.
> Do you still want to work up a patch for this?  If so, I can review.

Robert Haas
The Enterprise PostgreSQL Company

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