Horton

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

John Naylor <john.naylor@enterprisedb.com>

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From: John Naylor <john.naylor@enterprisedb.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>, Andres Freund <andres@anarazel.de>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2023-07-05T11:21:20Z
Lists: pgsql-hackers 
On Tue, Jul 4, 2023 at 12:49 PM Masahiko Sawada <sawada.mshk@gmail.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

Commits

  1. radixtree: Fix SIGSEGV at update of embeddable value to non-embeddable.

  2. Get rid of anonymous struct

  3. Teach radix tree to embed values at runtime

  4. Teach TID store to skip bitmap for small numbers of offsets

  5. Use bump context for TID bitmaps stored by vacuum

  6. Fix alignment of stack variable

  7. Use TidStore for dead tuple TIDs storage during lazy vacuum.

  8. Rethink create and attach APIs of shared TidStore.

  9. Fix inconsistent function prototypes with function definitions.

  10. Fix a calculation in TidStoreCreate().

  11. Fix potential integer handling issue in radixtree.h.

  12. Add TIDStore, to store sets of TIDs (ItemPointerData) efficiently.

  13. Fix link error for test_radixtree module on Windows

  14. Blind attempt to fix ODR violations

  15. Fix incorrect format specifier for int64

  16. Fix redefinition of typedefs

  17. Add template for adaptive radix tree

  18. Fix signedness error in 9f225e992 for gcc

  19. Introduce helper SIMD functions for small byte arrays

  20. Optimize vacuuming of relations with no indexes.

  21. Add bound check before bsearch() for performance

  22. Allocate consecutive blocks during parallel seqscans