From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
---|---|
To: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: How should pg_standby get over the gap of timeline? |
Date: | 2008-11-21 17:09:23 |
Message-ID: | 1227287363.7015.96.camel@hp_dx2400_1 |
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Lists: | pgsql-hackers |
On Thu, 2008-11-20 at 22:41 +0900, Fujii Masao wrote:
> In the current Synch Rep patch, the standby cannot catch up with the
> primary which has a bigger timeline. So, whenever making the standby
> catch up, a fresh base backup is required. This is obviously undesirable,
> and I'd like to get rid of this restriction.
>
> Postgres itself can recover up to a bigger timeline without a base
> backup. The remaining problem is that pg_standby cannot get over the
> gap of timeline. It continues waiting for the XLOG file with out-of-date
> timeline, and redo doesn't progress.
We've discussed this before. My answer is the same: you are assuming it
is safe to re-enter recovery, which is not correct (currently). You are
also assuming that taking a base backup is an expensive operation - it
need not be so if you simply move only the files/data that have changed,
e.g. rsync.
So if you want this to work, hacking pg_standby is not the way to do it.
But I'm not convinced there is a problem worth solving.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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