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

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?

--
John Naylor
EDB: http://www.enterprisedb.com