Re: Eliminate redundant tuple visibility check in vacuum

On Thu, Aug 31, 2023 at 6:29 PM Melanie Plageman
<melanieplageman@gmail.com> wrote:
> I have changed this.

I spent a bunch of time today looking at this, thinking maybe I could
commit it. But then I got cold feet.

With these patches applied, PruneResult ends up being declared in
heapam.h, with a comment that says /* State returned from pruning */.
But that comment isn't accurate. The two new members that get added to
the structure by 0002, namely nnewlpdead and htsv, are in fact state
that is returned from pruning. But the other 5 members aren't. They're
just initialized to constant values by pruning and then filled in for
real by the vacuum logic. That's extremely weird. It would be fine if
heap_page_prune() just grew a new output argument that only returned
the HTSV results, or perhaps it could make sense to bundle any
existing out parameters together into a struct and then add new things
to that struct instead of adding even more parameters to the function
itself. But there doesn't seem to be any good reason to muddle
together the new output parameters for heap_page_prune() with a bunch
of state that is currently internal to vacuumlazy.c.

I realize that the shape of the patches probably stems from the fact
that they started out life as part of a bigger patch set. But to be
committed independently, they need to be shaped in a way that makes
sense independently, and I don't think this qualifies. On the plus
side, it seems to me that it's probably not that much work to fix this
issue and that the result would likely be a smaller patch than what
you have now, which is something.

-- 
Robert Haas
EDB: http://www.enterprisedb.com