Re: Maximize page freezing

On Fri, Jul 29, 2022 at 5:55 AM Simon Riggs
<simon(dot)riggs(at)enterprisedb(dot)com> wrote:
> > I should be able to post something in a couple of weeks.
>
> How do you see that affecting this thread?

Well, it's clearly duplicative, at least in part. That in itself
doesn't mean much, but there are some general questions (that apply to
any variant of proactive/batched freezing), particularly around the
added overhead, and the question of whether or not we get to advance
relfrozenxid substantially in return for that cost. Those parts are
quite tricky.

I have every intention of addressing these thorny questions in my
upcoming patch set, which actually does far more than change the rules
about when and how we freeze -- changing the mechanism itself is very
much the easy part. I'm taking a holistic approach that involves
making an up-front decision about freezing strategy based on the
observed characteristics of the table, driven by what we see in the
visibility map at the start.

Similar questions will also apply to this patch, even though it isn't
as aggressive (your patch doesn't trigger freezing when a page is
about to be set all-visible in order to make sure that it can be set
all-frozen instead). You still want to give the user a clear benefit
for any added overhead. It needs a great deal of performance
validation, too.

--
Peter Geoghegan