Horton

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

Masahiko Sawada <sawada.mshk@gmail.com>

View thread View on postgr.es
From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Hannu Krosing <hannuk@google.com>
Cc: Peter Geoghegan <pg@bowt.ie>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-07-09T08:36:31Z
Lists: pgsql-hackers 
On Thu, Jul 8, 2021 at 10:40 PM Hannu Krosing <hannuk@google.com> wrote:
>
> Very nice results.
>
> I have been working on the same problem but a bit different solution -
> a mix of binary search for (sub)pages and 32-bit bitmaps for
> tid-in-page.
>
> Even with currebnt allocation heuristics (allocate 291 tids per page)
> it initially allocate much less space, instead of current 291*6=1746
> bytes per page it needs to allocate 80 bytes.
>
> Also it can be laid out so that it is friendly to parallel SIMD
> searches doing up to 8 tid lookups in parallel.

Interesting.

>
> That said, for allocating the tid array, the best solution is to
> postpone it as much as possible and to do the initial collection into
> a file, which
>
> 1) postpones the memory allocation to the beginning of index cleanups
>
> 2) lets you select the correct size and structure as you know more
> about the distribution at that time
>
> 3) do the first heap pass in one go and then advance frozenxmin
> *before* index cleanup

I think we have to do index vacuuming before heap vacuuming (2nd heap
pass). So do you mean that it advances relfrozenxid of pg_class before
both index vacuuming and heap vacuuming?

Regards,

--
Masahiko Sawada
EDB:  https://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