Re: Recovery target 'immediate'

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Recovery target 'immediate'
Date: 2013-04-26 13:48:48
Message-ID: 10163.1366984128@sss.pgh.pa.us
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Magnus Hagander <magnus(at)hagander(dot)net> writes:
> That said, maybe the easier choice for a *system* (such as v-thingy)
> would be to simply to the full backup using pg_basebackup -x (or
> similar), therefor not needing the log archive at all when restoring.
> Yes, it makes the base backup slightly larger, but also much
> simpler... As a bonus, your base backup would still work if you hosed
> your log archive.

It doesn't appear to me that that resolves Heikki's complaint: if you
recover from such a backup, the state that you get is still rather vague
no? The system will replay to the end of whichever WAL file it last
copied.

I think it'd be a great idea to ensure that pg_stop_backup creates a
well defined restore stop point that corresponds to some instant during
the execution of pg_stop_backup. Obviously, if other sessions are
changing the database state meanwhile, it's impossible to pin it down
more precisely than that; but I think this would satisfy the principle
of least astonishment, and it's not clear that what we have now does.

regards, tom lane

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