Re: pg_checksums?

Hi Peter,

> On Oct 29, 2023, at 11:49, Peter J. Holzer <hjp-pgsql(at)hjp(dot)at> wrote:
>
> It *might* work if there are zero writes on the primary during the
> downtime of the replica (because those writes couldn't be replicated),
> but that seems hard to ensure. Even if you could get away with making
> the primary read-only (is this even possible?) I wouldn't have much
> confidence in the result and reinit the (new) replica anyway.

As soon as I stop the replica to enable checksums, even writes can't get replicated anymore. So during enabling checksums, a replica is definitely protected against modifications by its primary, simply because it's down. The modifications of the primary are applied to the replica when it comes back online. So, I don't see a problem at this particular stage.

My fear is merely that enabling checksums does something to the physical state of the data files which are not compatible with the other side. Like for example manipulate the file headers in some way.

Maybe this question is better suited for the admin list than this general list?

Cheers
Paul