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From: Simon Riggs <simon.riggs@enterprisedb.com>
Date: Fri, 13 May 2022 13:31:13 +0100
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Subject: Re: Comments on Custom RMGRs
To: Jeff Davis <pgsql@j-davis.com>
Cc: Andres Freund <andres@anarazel.de>,
 PostgreSQL Hackers <pgsql-hackers@postgresql.org>
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On Fri, 13 May 2022 at 05:13, Jeff Davis <pgsql@j-davis.com> wrote:
>
> On Thu, 2022-05-12 at 22:26 +0100, Simon Riggs wrote:
> > I see multiple uses for the rm_checkpoint() point proposed and I've
> > been asked multiple times for a checkpoint hook.
>
> Can you elaborate and/or link to a discussion?

Those were conversations away from Hackers, but I'm happy to share.

The first was a discussion about a data structure needed by BDR about
4 years ago. In the absence of a pluggable checkpoint, the solution
was forced to use a normal table, which wasn't very satisfactory.

The second was a more recent conversation with Mike Stonebraker, at
the end of 2021.. He was very keen to remove the buffer manager
entirely, which requires that we have a new smgr, which then needs new
code to allow it to be written to disk at checkpoint time, which then
requires some kind of pluggable code at checkpoint time. (Mike was
also keen to remove WAL, but that's another story entirely!).

The last use case was unlogged indexes, which need to be read from
disk at startup or rebuilt after crash, which requires RmgrStartup to
work both with and without InRedo=true.

-- 
Simon Riggs                http://www.EnterpriseDB.com/