Re: [BUG] pg_basebackup from disconnected standby fails

From: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Magnus Hagander <magnus(at)hagander(dot)net>
Subject: Re: [BUG] pg_basebackup from disconnected standby fails
Date: 2016-10-27 04:21:54
Message-ID: CAB7nPqQ97UmsWaXCxdFsMkoZn+98ouch=2WQcLs9MEQZfWNX3g@mail.gmail.com
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On Thu, Oct 27, 2016 at 2:59 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Wed, Oct 26, 2016 at 2:06 AM, Michael Paquier
> <michael(dot)paquier(at)gmail(dot)com> wrote:
>> But yes, thinking *harder*, I agree that updating minRecoveryPoint
>> just after the checkpoint record would be fine and removes the need to
>> have more WAL than necessary in for a backup taken from a standby.
>> That will also prevent cases where minRecoveryPoint is older than the
>> recovery start point. On top of that the cost of an extra call to
>> UpdateControlFile() looks cheap considering that CreateRestartPoint()
>> is called only by the checkpointer or at shutdown.
>>
>> Just coding things this solution gives roughtly the attached? The TAP
>> test passes btw.
>
> I think that still leaves a race condition, right? It's got to be
> part of the SAME control file update that advances the redo pointer.

Right, thanks for double-checking... There is no meaning to do that
out of the ControlFileLock taken previously...
--
Michael

Attachment Content-Type Size
backup-standby-v5.patch text/plain 1.9 KB

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