Re: [BUGS] Breakage with VACUUM ANALYSE + partitions

From: Andres Freund <andres(at)anarazel(dot)de>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Thom Brown <thom(at)linux(dot)com>, Abhijit Menon-Sen <ams(at)2ndquadrant(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [BUGS] Breakage with VACUUM ANALYSE + partitions
Date: 2016-05-02 16:41:11
Message-ID: 20160502164111.cpupbbkab6ik7wwd@alap3.anarazel.de
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On 2016-05-02 12:29:45 -0400, Robert Haas wrote:
> On Fri, Apr 29, 2016 at 7:58 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > Basically the reason for the problem is that mdsync() needs to access
> > "formally non-existant segments" (as in ones where previous segments are
> > < RELSEG_SIZE), because we queue (and the might be preexistant) fsync
> > requests via register_dirty_segment() in mdtruncate().
>
> Shouldn't we just throw those flush requests away?

Well, we explicity make them for truncations (register_dirty_segment()
calls in mdtruncate()). There's no comment as to why - I suspect the
idea is that you want to make sure the truncation sticks in case of
crash?

FWIW, falling back to _mdfd_openseg() fixes the issue.

Andres

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