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Re: New sync commit mode remote_write

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: Magnus Hagander <magnus(at)hagander(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: New sync commit mode remote_write
Date: 2012-04-24 20:51:34
Message-ID: CA+TgmoaPVnuofFRckqBDdOJ820bvfiTqkft3paYkn6tzaUO5Mw@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, Apr 24, 2012 at 12:21 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> On Thu, Apr 19, 2012 at 11:50 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On 4/19/12, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>>> The work around would be for the master to refuse to automatically
>>> restart after a crash, insisting on a fail-over instead (or a manual
>>> forcing of recovery)?
>>
>> I suppose that would work, but I think Simon's idea is better: don't
>> let the slave replay the WAL until either (a) it's promoted or (b) the
>> master finishes the fsync.   That boils down to adding some more
>> handshaking to the replication protocol, I think.
>
> Alternative c) is that the master automatically recovers from a crash,
> but doesn't replay that particular wal record because it doesn't find
> it on disk, so the slave has to be instructed to throw it away.

Right.  Which kind of stinks.

> (Or
> perhaps the slave could feed the wal back to the master, so the master
> could replay it?)

Yes, that would be a very nice enhancement, I think.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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