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

On Wed, Jul 5, 2023 at 8:21 PM John Naylor <john(dot)naylor(at)enterprisedb(dot)com> wrote:
>
> On Tue, Jul 4, 2023 at 12:49 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > As you mentioned, the 1-byte value is embedded into 8 byte so 7 bytes
> > are unused, but we use less memory since we use less slab contexts and
> > save fragmentations.
>
> Thanks for testing. This tree is sparse enough that most of the space is taken up by small inner nodes, and not by leaves. So, it's encouraging to see a small space savings even here.
>
> > I've also tested some large value cases (e.g. the value is 80-bytes)
> > and got a similar result.
>
> Interesting. With a separate allocation per value the overhead would be 8 bytes, or 10% here. It's plausible that savings elsewhere can hide that, globally.
>
> > Regarding the codes, there are many todo and fixme comments so it
> > seems to me that your recent work is still in-progress. What is the
> > current status? Can I start reviewing the code or should I wait for a
> > while until your recent work completes?
>
> Well, it's going to be a bit of a mess until I can demonstrate it working (and working well) with bitmap heap scan. Fixing that now is just going to create conflicts. I do have a couple small older patches laying around that were quick experiments -- I think at least some of them should give a performance boost in loading speed, but haven't had time to test. Would you like to take a look?

Yes, I can experiment with these patches in the meantime.

Regards,

--
Masahiko Sawada
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