Re: Offline enabling/disabling of data checksums

Hi,

On 2019-03-20 07:55:39 +0100, Fabien COELHO wrote:
> > And you're basically adding it because Fabien doesn't like
> > postmaster.pid and wants to invent another lockout mechanism in this
> > thread.
>
> I did not suggest to rename the control file, but as it is already done by
> another command it did not look like a bad idea in itself, or at least an
> already used bad idea:-)

pg_upgrade in link mode intentionally wants to *permanently* disable a
cluster. And it explicitly writes a log message about it. That's not a
case to draw inferrence for this case.

> I'd be okay with anything that works consistently accross all commands that
> may touch a cluster and are mutually exclusive (postmater, pg_rewind,
> pg_resetwal, pg_upgrade, pg_checksums…), without underlying race conditions.
> It could be locking, a control file state, a special file (which one ? what
> is the procedure to create/remove it safely and avoid potential race
> conditions ?), possibly "postmaster.pid", whatever really.
>
> I'll admit that I'm moderately enthousiastic about "posmaster.pid" because
> it does not do anymore what the file names says, but if it really works and
> is used consistently by all commands, why not. In case of unexpected
> problems, the file will probably have to be removed/fixed by hand. I also
> think that the implemented mechanism should be made available in
> "control_utils.c", not duplicated in every command.

That's just a separate feature.

Greetings,

Andres Freund