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In-Reply-To: <20220217110515.zssjnez4lq2lmrdq@jrouhaud>
From: Nitin Jadhav <nitinjadhavpostgres@gmail.com>
Date: Thu, 17 Feb 2022 22:39:02 +0530
Message-ID: <CAMm1aWZ1YY6n8T=0OkwQJJdua7fpkJdKr1fRqfTSrJb1ME9Q5g@mail.gmail.com>
Subject: Re: Report checkpoint progress with pg_stat_progress_checkpoint (was:
 Report checkpoint progress in server logs)
To: Julien Rouhaud <rjuju123@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, 
	Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Bruce Momjian <bruce@momjian.us>, 
	Tom Lane <tgl@sss.pgh.pa.us>, Magnus Hagander <magnus@hagander.net>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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> > Thank you for sharing the information.  'triggering backend PID' (int)
> > - can be stored without any problem.
>
> There can be multiple processes triggering a checkpoint, or at least wanting it
> to happen or happen faster.

Yes. There can be multiple processes but there will be one checkpoint
operation at a time. So the backend PID corresponds to the current
checkpoint operation. Let me know if I am missing something.

> > 'checkpoint or restartpoint?'
>
> Do you actually need to store that?  Can't it be inferred from
> pg_is_in_recovery()?

AFAIK we cannot use pg_is_in_recovery() to predict whether it is a
checkpoint or restartpoint because if the system exits from recovery
mode during restartpoint then any query to pg_stat_progress_checkpoint
view will return it as a checkpoint which is ideally not correct. Please
correct me if I am wrong.

Thanks & Regards,
Nitin Jadhav

On Thu, Feb 17, 2022 at 4:35 PM Julien Rouhaud <rjuju123@gmail.com> wrote:
>
> Hi,
>
> On Thu, Feb 17, 2022 at 12:26:07PM +0530, Nitin Jadhav wrote:
> >
> > Thank you for sharing the information.  'triggering backend PID' (int)
> > - can be stored without any problem.
>
> There can be multiple processes triggering a checkpoint, or at least wanting it
> to happen or happen faster.
>
> > 'checkpoint or restartpoint?'
>
> Do you actually need to store that?  Can't it be inferred from
> pg_is_in_recovery()?