Re: New strategies for freezing, advancing relfrozenxid early

On Fri, Dec 30, 2022 at 1:12 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> > "Nominal freezing" is happening when there are no freeze plans at all.
> > I get that it's to manage control flow so that the right thing happens
> > later. But I think it should be defined in terms of what state the page
> > is in so that we know that following a given path is valid. Defining
> > "nominal freezing" as a case where there are no freeze plans is just
> > confusing to me.
>
> What would you prefer? The state that the page is in is not something
> that I want to draw much attention to, because it's confusing in a way
> that mostly isn't worth talking about.

I probably should have addressed what you said more directly. Here goes:

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. OTOH, following the
"no freeze" path is permissible whenever the freeze_required flag
hasn't been set during any call to heap_prepare_freeze_tuple(). It is
never actually mandatory for lazy_scan_prune() to *not* freeze.

It's a bit like how a simple point can be understood as a degenerate
circle of radius 0. It's an abstract definition, which is just a tool
for describing things precisely -- hopefully a useful tool. I welcome
the opportunity to be able to describe things in a way that is clearer
or more useful, in whatever way. But it's not like I haven't already
put in significant effort to this exact question of what "freezing the
page" really means to lazy_scan_prune(). Naming things is hard.

--
Peter Geoghegan