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: Robert Haas <robertmhaas@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-07-30T19:34:12Z
Lists: pgsql-hackers 
Hi,

On 2021-07-30 15:13:49 -0400, Robert Haas wrote:
> On Thu, Jul 29, 2021 at 3:14 PM Andres Freund <andres@anarazel.de> wrote:
> > I think those advantages are far outstripped by the big disadvantage of
> > needing to either size the array accurately from the start, or to
> > reallocate the whole array.  Our current pre-allocation behaviour is
> > very wasteful for most vacuums but doesn't handle large work_mem at all,
> > causing unnecessary index scans.
> 
> I agree that the current pre-allocation behavior is bad, but I don't
> really see that as an issue with my idea. Fixing that would require
> allocating the array in chunks, but that doesn't really affect the
> core of the idea much, at least as I see it.

Well, then it'd not really be the "simple array approach" anymore :)


> But I accept that Yura has a very good point about the memory usage of
> what I was proposing.

The lower memory usage also often will result in a better cache
utilization - which is a crucial factor for index vacuuming when the
index order isn't correlated with the heap order. Cache misses really
are a crucial performance factor there.

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