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Re: warning message in standby

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <bruce(at)momjian(dot)us>, Magnus Hagander <magnus(at)hagander(dot)net>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: warning message in standby
Date: 2010-06-29 10:59:39
Message-ID: AANLkTimqSmAzB0-QVgzkaypW-GB3M3j0UbvqvvPEgPTs@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, Jun 29, 2010 at 3:55 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> On Tue, Jun 15, 2010 at 11:35 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>> On the other hand, I like immediate-panicking. And I don't want the standby
>> to retry reconnecting the master infinitely.
>
> On second thought, the peremptory PANIC is not good for HA system. If the
> master unfortunately has written an invalid record because of its crash,
> the standby would exit with PANIC before performing a failover.

I don't think that should ever happen.  The master only streams WAL
that it has fsync'd.  Presumably there's no reason for the master to
ever fsync a partial WAL record (which is usually how a corrupt record
gets into the stream).

> So when an invalid record is found in streamed WAL file, we should keep
> the standby running and leave the decision whether the standby retries to
> connect to the master forever or shuts down right now, up to the user
> (actually, it may be a clusterware)?

Well, if we want to leave it up to the user/clusterware, the current
code is possibly adequate, although there are many different log
messages that could signal this situation, so coding it up might not
be too trivial.

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

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