Horton

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

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Yura Sokolov <y.sokolov@postgrespro.ru>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-07-28T18:41:39Z
Lists: pgsql-hackers 
Hi,


On 2021-07-25 19:07:18 +0300, Yura Sokolov wrote:
> I've dreamed to write more compact structure for vacuum for three
> years, but life didn't give me a time to.
> 
> Let me join to friendly competition.
> 
> I've bet on HATM approach: popcount-ing bitmaps for non-empty elements.

My concern with several of the proposals in this thread is that they
over-optimize for this specific case. It's not actually that crucial to
have a crazily optimized vacuum dead tid storage datatype. Having
something more general that also performs reasonably for the dead tuple
storage, but also performs well in a number of other cases, makes a lot
more sense to me.


> (Bad radix result probably due to smaller cache in notebook's CPU ?)

Probably largely due to the node dispatch. a) For some reason gcc likes
jump tables too much, I get better numbers when disabling those b) the
node type dispatch should be stuffed into the low bits of the pointer.


> select prepare(1000000, 2, 100, 1);
> 
>        attach  size   shuffled
> array    6ms    12MB   53.42s
> intset  23ms    16MB   54.99s
> rtbm   115ms    38MB    8.19s
> tbm    186ms   100MB    8.37s
> vtbm   105ms    59MB    9.08s
> radix   64ms    42MB   10.41s
> svtm    73ms    10MB    7.49s

> Test4
> 
> select prepare(1000000, 100, 1, 1);
> 
>        attach  size   shuffled
> array  304ms   600MB   75.12s
> intset 775ms    98MB   47.49s
> rtbm   356ms    38MB    4.11s
> tbm    539ms   100MB    4.20s
> vtbm   493ms    42MB    4.44s
> radix  263ms    42MB    6.05s
> svtm   360ms     8MB    3.49s
> 
> Therefore Specialized Vaccum Tid Map always consumes least memory amount
> and usually faster.

Impressive.

Greetings,

Andres Freund

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