Re: Documentation fixes for pg_visibility

Robert wrote:
> I think there should probably be a test for
> all_visible_according_to_vm at the beginning of that so that we don't
> add more visibility map checks for pages where we already know the VM
> bit can't possibly be set.

Yes, that looks like a good idea after more screening of this code.

On Wed, Jul 6, 2016 at 12:21 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> So I'm a bit confused about what you are saying here. If the page is
> marked all-frozen but actually isn't all-frozen, then we should clear
> the all-frozen bit in the VM. The easiest way to do that is to clear
> both bits in the VM plus the page-level bit, as done here, because we
> don't presently have a way of clearing just one of the visibility map
> bits.

Yes, that's my understanding as well for what is necessary: clear both
bits in the vm as well as the bit on the page itself, and mark it as
dirty. Way to go.

> Now, since the heap_lock_tuple issue requires us to introduce a new
> method to clear all-visible without clearing all-frozen, we could
> possibly use that here too, once we have it.

For 10.0, working on lower-level routine optimizations of this kind
sounds good to me. But I vote against this level of code reordering in
9.6 post-beta2 if that's what you suggest.
--
Michael