Re: [HACKERS] pgsql: Fix freezing of a dead HOT-updated tuple

On Thu, Nov 9, 2017 at 4:53 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> Primarily because it's not an anti-corruption tool. I'd be surprised if
> there weren't ways to corrupt the page using these corruptions that
> aren't detected by it.

It's very hard to assess the risk of missing something that's actually
detectable with total confidence, but I think that the check is actually
very thorough.

> But even if it were, I don't think there's
> enough information to do so in the general case. You very well can end
> up with pages where subsequent hot pruning has removed a good bit of the
> direct evidence of this bug.

Sure, but maybe those are cases that can't get any worse anyway. So the
question of avoiding making it worse doesn't arise.

> But I'm not really sure why the error detection capabilities of matter
> much for the principal point I raised, which is how much work we need to
> do to not further worsen the corruption.

You're right. Just trying to put the risk in context, and to understand the
extent of the concern that you have.

--
Peter Geoghegan