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From: Stephen Frost <sfrost@snowman.net>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-bugs@lists.postgresql.org, Michael Paquier <michael@paquier.xyz>
Cc: Alexander Kukushkin <cyberdemn@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Subject: Re: BUG #15346: Replica fails to start after the crash
Date: Tue, 28 Aug 2018 08:23:11 -0400
Message-ID: <20180828122311.GD3326@tamriel.snowman.net> (raw)
In-Reply-To: <3B69F535-FD81-461B-97E9-657D4C99EDB4@anarazel.de>
References: <CA+q6zcVjv1Lp-3=prBbpq2CbBioK91SHarfw3F8FHuUN4EwcUA@mail.gmail.com>
	<20180822175034.lnvwk5js32k6mjyz@alvherre.pgsql>
	<20180823041420.GA1158@paquier.xyz>
	<CAFh8B==4gpwor6ODercru0iifqwd0nQrdRvXzmorWkMRQa4q=g@mail.gmail.com>
	<CAFh8B=nHdsX83hTZMqGqbht39ud+DRQOv4_Te+xu3DuPssQbZA@mail.gmail.com>
	<CAFh8B=mYGP1J8ueHKU40Dr4bNBUPJj1rTbZ6Wpg4gR30uCRunA@mail.gmail.com>
	<20180828024409.GB29157@paquier.xyz>
	<3B69F535-FD81-461B-97E9-657D4C99EDB4@anarazel.de>

Greetings,

* Andres Freund (andres@anarazel.de) wrote:
> On August 28, 2018 11:44:09 AM GMT+09:00, Michael Paquier <michael@paquier.xyz> wrote:
> >On Sat, Aug 25, 2018 at 09:54:39AM +0200, Alexander Kukushkin wrote:
> >> Why the number of tuples in the xlog is greater than the number of
> >> tuples on the index page?
> >> Because this page was already overwritten and its LSN is HIGHER than
> >> the current LSN!
> >
> >That's annoying.  Because that means that the control file of your
> >server maps to a consistent point which is older than some of the
> >relation pages.  How was the base backup of this node created?  Please
> >remember that when taking a base backup from a standby, you should
> >backup the control file last, as there is no control of end backup with
> >records available.  So it seems to me that the origin of your problem
> >comes from an incorrect base backup expectation? 
> 
> Uh, where is that "control file last" bit coming from?

pg_basebackup copies it last.  The comments should probably be improved
as to *why* but my recollection is that it's, at least in part, to
ensure the new cluster can't be used until it's actually a complete
backup.

Thanks!

Stephen

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  To: pgsql-bugs@postgresql.org
  Cc: sfrost@snowman.net, andres@anarazel.de, michael@paquier.xyz, cyberdemn@gmail.com, alvherre@2ndquadrant.com, 9erthalion6@gmail.com
  Subject: Re: BUG #15346: Replica fails to start after the crash
  In-Reply-To: <20180828122311.GD3326@tamriel.snowman.net>

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