Re: Changing the state of data checksums in a running cluster

Hi,

On 2025-11-21 01:44:31 +0100, Andreas Karlsson wrote:
> On 11/20/25 11:34 AM, Tomas Vondra wrote:
> > On 11/19/25 22:03, Andreas Karlsson wrote:
> > > I have been following these discussions but not read the patch in detail.
> > > 
> > > This patch makes me worried especially with the new issues recently
> > > uncovered. This was already a quite big patch and to fix these issues it
> > > will likely have to become even bigger and given how this would become a
> > > very rarely stressed code paths I wonder if we can actually ever become
> > > confident that the patch works in all edge cases.
> > > 
> > > Something like this need to be easy to understand for us to have any
> > > hope at all to be comfortable in the correctness. Can we actually do that?
> > > 
> > 
> > How's this different from any other complex patch? We get more familiar
> > with the problem during review, identify issues, improve the patch to
> > address them. And then again and again.
> 
> The difference I see is in how rarely anyone actually switches checksum
> state in a production database, especially now that we enabled them by
> default. A complex and rarely stressed code path is a minefield.

FWIW, I think this is actually a good feature build the infrastructure for
features (i.e. dynamically reconfiguring the cluster while running) like this,
precisely because it isn't *constantly* used.

Greetings,

Andres Freund