Re: [PoC] Improve dead tuple storage for lazy vacuum

Hi,

On 2021-07-30 15:13:49 -0400, Robert Haas wrote:
> On Thu, Jul 29, 2021 at 3:14 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > I think those advantages are far outstripped by the big disadvantage of
> > needing to either size the array accurately from the start, or to
> > reallocate the whole array. Our current pre-allocation behaviour is
> > very wasteful for most vacuums but doesn't handle large work_mem at all,
> > causing unnecessary index scans.
>
> I agree that the current pre-allocation behavior is bad, but I don't
> really see that as an issue with my idea. Fixing that would require
> allocating the array in chunks, but that doesn't really affect the
> core of the idea much, at least as I see it.

Well, then it'd not really be the "simple array approach" anymore :)

> But I accept that Yura has a very good point about the memory usage of
> what I was proposing.

The lower memory usage also often will result in a better cache
utilization - which is a crucial factor for index vacuuming when the
index order isn't correlated with the heap order. Cache misses really
are a crucial performance factor there.

Greetings,

Andres Freund