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From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Thu, 27 Jan 2022 20:37:37 +0530
Message-ID: <CALj2ACUfLrN8XGn0ZNrAou5eoDwMnFGnDE9rhcs8==jmtSd4WA@mail.gmail.com>
Subject: Re: Add checkpoint and redo LSN to LogCheckpointEnd log message
To: "Bossart, Nathan" <bossartn@amazon.com>
Cc: Julien Rouhaud <rjuju123@gmail.com>, Michael Paquier <michael@paquier.xyz>, 
	Kyotaro Horiguchi <horikyota.ntt@gmail.com>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Thu, Jan 20, 2022 at 6:06 AM Bossart, Nathan <bossartn@amazon.com> wrote:
>
> On 1/3/22, 5:52 PM, "Kyotaro Horiguchi" <horikyota.ntt@gmail.com> wrote:
> > It seems to me "LSN" or just "location" is more confusing or
> > mysterious than "REDO LSN" for the average user. If we want to avoid
> > being technically too detailed, we would use just "start LSN=%X/%X,
> > end LSN=%X/%X".  And it is equivalent to "WAL range=[%X/%X, %X/%X]"..
>
> My first instinct was that this should stay aligned with
> pg_controldata, but that would mean using "location=%X/%X, REDO
> location=%X/%X," which doesn't seem terribly descriptive.  IIUC the
> "checkpoint location" is the LSN of the WAL record for the checkpoint,
> and the "checkpoint's REDO location" is the LSN where checkpoint
> creation began (i.e., what you must retain for crash recovery).  My
> vote is for "start=%X/%X, end=%X/%X."

I'm still not clear how the REDO location can be treated as a start
LSN? Can someone throw some light one what this checkpoint's REDO
location is?

Regards,
Bharath Rupireddy.