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: 2024-03-06T03:59:34Z
Lists: pgsql-hackers 
On Tue, Mar 5, 2024 at 11:12 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Tue, Mar 5, 2024 at 6:41 PM John Naylor <johncnaylorls@gmail.com> wrote:

> > Done in v66-0009. I'd be curious to hear any feedback. I like the
> > aspect that the random numbers come from a different seed every time
> > the test runs.
>
> The new tests look good. Here are some comments:
>
> ---
> +               expected = keys[i];
> +               iterval = rt_iterate_next(iter, &iterkey);
>
> -               ndeleted++;
> +               EXPECT_TRUE(iterval != NULL);
> +               EXPECT_EQ_U64(iterkey, expected);
> +               EXPECT_EQ_U64(*iterval, expected);
>
> Can we verify that the iteration returns keys in ascending order?

We get the "expected" value from the keys we saved in the now-sorted
array, so we do already. Unless I misunderstand you.

> ---
> +     /* reset random number generator for deletion */
> +     pg_prng_seed(&state, seed);
>
> Why is resetting the seed required here?

Good catch - My intention was to delete in the same random order we
inserted with. We still have the keys in the array, but they're sorted
by now. I forgot to go the extra step and use the prng when generating
the keys for deletion -- will fix.

> ---
> The radix tree (and dsa in TSET_SHARED_RT case) should be freed at the end.

Will fix.

> ---
>     radixtree_ctx = AllocSetContextCreate(CurrentMemoryContext,
>                                           "test_radix_tree",
>                                           ALLOCSET_DEFAULT_SIZES);
>
> We use a mix of ALLOCSET_DEFAULT_SIZES and ALLOCSET_SMALL_SIZES. I
> think it's better to use either one for consistency.

Will change to "small", since 32-bit platforms will use slab for leaves.

I'll look at the memory usage and estimate what 32-bit platforms will
use, and maybe adjust the number of keys. A few megabytes is fine, but
not many megabytes.

> > I'd like to push 0001 and 0002 shortly, and then do another sweep over
> > 0003, with remaining feedback, and get that in so we get some
> > buildfarm testing before the remaining polishing work on
> > tidstore/vacuum.
>
> Sounds a reasonable plan. 0001 and 0002 look good to me. I'm going to
> polish tidstore and vacuum patches and update commit messages.

Sounds good.

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