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Re: Streaming replication, and walsender during recovery

From: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Streaming replication, and walsender during recovery
Date: 2010-01-19 06:04:06
Message-ID: 3f0b79eb1001182204w4dc1f348qf94970703d1708df@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Jan 18, 2010 at 11:42 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On Mon, 2010-01-18 at 09:31 -0500, Tom Lane wrote:
>> Fujii Masao <masao(dot)fujii(at)gmail(dot)com> writes:
>> > When I configured a cascaded standby (i.e, made the additional
>> > standby server connect to the standby), I got the following
>> > errors, and a cascaded standby didn't start replication.
>>
>> >   ERROR:  timeline 0 of the primary does not match recovery target timeline 1
>>
>> > I didn't care about that case so far. To avoid a confusing error
>> > message, we should forbid a startup of walsender during recovery,
>> > and emit a suitable message? Or support such cascade-configuration?
>> > Though I don't think that the latter is difficult to be implemented,
>> > ISTM it's not the time to do that now.
>>
>> It would be kind of silly to add code to forbid it if making it work
>> would be about the same amount of effort.  I think it'd be worth looking
>> closer to find out what the problem is.
>
> There is an ERROR, but no problem AFAICS. The tli isn't set until end of
> recovery because it doesn't need to have been set yet. That shouldn't
> prevent retrieving WAL data.

OK. Here is the patch which supports a walsender process during recovery;

* Change walsender so as to send the WAL written by the walreceiver
  if it has been started during recovery.
* Kill the walsenders started during recovery at the end of recovery
  because replication cannot survive the change of timeline ID.

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

Attachment: walsender_during_recovery_0119.patch
Description: text/x-patch (2.8 KB)

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