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Re: incorrect handling of the timeout in pg_receivexlog

From: Magnus Hagander <magnus(at)hagander(dot)net>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: incorrect handling of the timeout in pg_receivexlog
Date: 2012-02-07 16:33:39
Message-ID: CABUevEwwJ-A7XFhT2adBp9ZDyQE9ADfLJVe9szayCsgKJ1tasA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, Feb 7, 2012 at 17:29, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> On 07.02.2012 16:55, Tom Lane wrote:
>>
>> (The integer vs float TimestampTz issue is a kind of portability
>> problem, but we've already bought into the assumption that sender and
>> receiver must be built with the same choice, no?)
>
>
> Hmm, true. In hindsight, I think that was a bad choice, but it's a bit late
> to change that. pg_basebackup doesn't otherwise care about the integer/float
> timestamps, but it does send a timestamp back to the server. You won't be
> able to actually start up the database if the config options don't match,
> but I think it would be good if pg_basebackup still worked across platforms
> and versions. For example, you might have a central backup server that calls
> pg_basebackup on several database servers, running on different platforms.
>
> In 9.0, the only field in the protocol that depends on timestamp format is
> WalDataMessageHeader->sendTime. That goes from server to client, and
> pg_basebackup/pg_receivexlog don't care about that. In 9.1 we introduced
> StandbyReplyMessage->sendTime, which is sent from client to server, but
> looking at the code it looks like the server doesn't use it for anything. In
> 9.2, we added WalSndrMessage->sendTime, which is used by a standby server to
> calculate how far behind the standby is.
>
> I'm tempted to just change all of those TimestampTz fields to something
> that's independent of integer/float timestamp setting, in 9.2. At a quick
> glance, it seems that it wouldn't break anything.

In general, I think that would work. Since we can't replicate across
versions anyway.

Will it break using pg_basebackup 9.2 on a 9.1 server, though? that
would also be very useful in the scenario of the central server...

-- 
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

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