Re: Online enabling of checksums

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Robert Haas <robertmhaas(at)gmail(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, Andrey Borodin <x4mmm(at)yandex-team(dot)ru>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Michael Banck <michael(dot)banck(at)credativ(dot)de>, Greg Stark <stark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Online enabling of checksums
Date: 2018-08-01 16:36:13
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On Tue, Jul 31, 2018 at 04:05:23PM -0700, Andres Freund wrote:
> Hi,
> On 2018-07-31 18:56:29 -0400, Alvaro Herrera wrote:
> > In the spirit of supporting incremental development, I think it's quite
> > sensible to get the current thing done, then see what it takes to get
> > the next thing done. Each is an improvement on its own merits. And it
> > doesn't have to be made by the same people.
> I just don't buy this. An earlier version of this feature was committed
> to v11 without the restart, over objections. There's now extra state in
> the control file to support the restart based system, there's extra
> tests, extra docs. And it'd not be much code to just make it work
> without the restart. The process around this patchset is just plain
> weird. ----------------------------------------------

This patchset is weird because it is perhaps our first case of trying to
change the state of the server while it is running. We just don't have
an established protocol for how to orchestrate that, so we are limping
along toward a solution. Forcing a restart is probably part of that
primitive orchestration. We will probably have similar challenges if we
ever allowed Postgres to change its data format on the fly. These
challenges are one reason pg_upgrade only modifies the new cluster,
never the old one.

Bruce Momjian <bruce(at)momjian(dot)us>

+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +

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