Horton

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

John Naylor <johncnaylorls@gmail.com>

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From: John Naylor <johncnaylorls@gmail.com>
To: Masahiko Sawada <sawada.mshk@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: 2024-03-21T03:40:05Z
Lists: pgsql-hackers 
On Thu, Mar 21, 2024 at 9:37 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Wed, Mar 20, 2024 at 11:19 PM John Naylor <johncnaylorls@gmail.com> wrote:
> > Are they (the blocks to be precise) really out of order? The VALUES
> > statement is ordered, but after inserting it does not output that way.
> > I wondered if this is platform independent, but CI and our dev
> > machines haven't failed this test, and I haven't looked into what
> > determines the order. It's easy enough to hide the blocks if we ever
> > need to, as we do elsewhere...
>
> It seems not necessary as such a test is already covered by
> test_radixtree. I've changed the query to hide the output blocks.

Okay.

> The buildfarm has been all-green so far.

Great!

> I've attached the latest vacuum improvement patch.
>
> I just remembered that the tidstore cannot still be used for parallel
> vacuum with minimum maintenance_work_mem. Even when the shared
> tidstore is empty, its memory usage reports 1056768 bytes, a bit above
> 1MB (1048576 bytes). We need something discussed on another thread[1]
> in order to make it work.

For exactly this reason, we used to have a clamp on max_bytes when it
was internal to tidstore, so that it never reported full when first
created, so I guess that got thrown away when we got rid of the
control object in shared memory. Forcing callers to clamp their own
limits seems pretty unfriendly, though.

The proposals in that thread are pretty simple. If those don't move
forward soon, a hackish workaround would be to round down the number
we get from dsa_get_total_size to the nearest megabyte. Then
controlling min/max segment size would be a nice-to-have for PG17, not
a prerequisite.

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