Horton

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

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: John Naylor <johncnaylorls@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>, Nathan Bossart <nathandbossart@gmail.com>, Andres Freund <andres@anarazel.de>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>
Date: 2023-12-21T01:32:37Z
Lists: pgsql-hackers 
On Thu, Dec 21, 2023 at 10:19 AM John Naylor <johncnaylorls@gmail.com> wrote:
>
> On Wed, Dec 20, 2023 at 6:36 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > I've updated the new patch set that incorporated comments I got so
> > far. 0007, 0008, and 0012 patches are updates from the v45 patch set.
> > In addition to the review comments, I made some changes in tidstore to
> > make it independent from heap. Specifically, it uses MaxOffsetNumber
> > instead of MaxHeapTuplesPerPage. Now we don't need to include
> > htup_details.h. It enlarged MaxBlocktableEntrySize but it's still 272
> > bytes.
>
> That's a good idea.
>
> > BTW regarding the previous comment I got before:
> >
> > > - RT_PTR_ALLOC *slot;
> > > + RT_PTR_ALLOC *slot = NULL;
> > >
> > > We have a macro for invalid pointer because of DSA.
> >
> > I think that since *slot is a pointer to a RT_PTR_ALLOC it's okay to set NULL.
>
> Ah right, it's the address of the slot.
>
> > I'm going to update RT_DUMP() and RT_DUMP_NODE() codes for the next step.
>
> That could probably use some discussion. A few months ago, I found the
> debugging functions only worked when everything else worked. When
> things weren't working, I had to rip one of these functions apart so
> it only looked at one node. If something is broken, we can't count on
> recursion or iteration working, because we won't get that far. I don't
> remember how things are in the current patch.

Agreed.

I found the following comment and wanted to discuss:

// this might be better as "iterate over nodes", plus a callback to
RT_DUMP_NODE,
// which should really only concern itself with single nodes
RT_SCOPE void
RT_DUMP(RT_RADIX_TREE *tree)

If it means we need to somehow use the iteration functions also for
dumping the whole tree, it would probably need to refactor the
iteration codes so that the RT_DUMP() can use them while dumping
visited nodes. But we need to be careful of not adding overheads to
the iteration performance.

>
> I've finished the node shrinking and addressed some fixme/todo areas
> -- can I share these and squash your v46 changes first?

Cool! Yes, please do so.

Regards,

-- 
Masahiko Sawada
Amazon Web Services: https://aws.amazon.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