Re: New strategies for freezing, advancing relfrozenxid early

On Sat, Dec 31, 2022 at 11:46 AM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> On Fri, 2022-12-30 at 16:58 -0800, Peter Geoghegan wrote:
> > Following the path of freezing a page is *always* valid, by
> > definition. Including when there are zero freeze plans to execute, or
> > even zero tuples to examine in the first place -- we'll at least be
> > able to perform nominal freezing, no matter what.
>
> This is a much clearer description, in my opinion. Do you think this is
> already reflected in the comments (and I missed it)?

I am arguably the person least qualified to answer this question. :-)

> Perhaps the comment in the "if (tuples_frozen == 0)" branch could be
> something more like:
>
> "We have no freeze plans to execute, so there's no cost to following
> the freeze path. This is important in the case where the page is
> entirely frozen already, so that the page will be marked as such in the
> VM."

I'm happy to use your wording instead -- I'll come up with a patch for that.

In my mind it's just a restatement of what's there already. I assume
that you're right about it being clearer this way.

> Of course, I'm sure there are some nuances that I'm still missing.

I don't think that there is, actually. I now believe that you totally
understand the mechanics involved here. I'm glad that I was able to
ascertain that that's all it was. It's worth going to the trouble of
getting something like this exactly right.

--
Peter Geoghegan