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Re: Stefan's bug (was: max_standby_delay considered harmful)

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>, Simon Riggs <simon@2ndquadrant.com>, Andres Freund <andres@anarazel.de>, Florian Pflug <fgp@phlo.org>, Dimitri Fontaine <dfontaine@hi-media.com>, Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers <pgsql-hackers@postgresql.org>, Bruce Momjian <bruce@momjian.us>, Greg Smith <greg@2ndquadrant.com>, Josh Berkus <josh@agliodbs.com>
Date: 2010-05-17T11:02:56Z
Lists: pgsql-hackers 
On Mon, May 17, 2010 at 3:38 AM, Fujii Masao <masao.fujii@gmail.com> wrote:
> On Mon, May 17, 2010 at 10:25 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>> Therefore I think
>> Fujii Masao's original idea was the best, but I have what I believe is
>> an equivalent but simpler implementation, which is attached.
>
> Seems good.
>
> I found another two problems related to shutdown in PM_STARTUP state:
>
> (1)
> Smart or fast shutdown requested in PM_STARTUP state always removes
> the backup_label file if it exists. But it might be still required
> for subsequent recovery. I changed your patch so that additionally
> the postmaster skips deleting the backup_label in that case.

Can you explain in a little more detail how this can cause a problem?
I'm not very familiar with how the backup label is used.

Also, why is this different in PM_STARTUP than in PM_RECOVERY?
PM_RECOVERY doesn't guarantee that we've reached consistency.

> (2)
> pg_ctl -ms stop emits the following warning whenever there is the
> backup_label file in $PGDATA.
>
>      WARNING: online backup mode is active
>      Shutdown will not complete until pg_stop_backup() is called.
>
> This warning doesn't fit in with the shutdown during recovery case.
> Since smart shutdown might be requested by other than pg_ctl, the
> warning should be emitted in server side rather than client, I think.
> How about moving the warning to the server side?

Hmm, I'm not sure whether that's a good idea or not.  Perhaps we
should discuss for 9.1?

-- 
Robert Haas
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