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: Noah Misch <noah@leadboat.com>
Cc: John Naylor <johncnaylorls@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2024-04-25T02:49:38Z
Lists: pgsql-hackers

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On Thu, Apr 25, 2024 at 6:03 AM Noah Misch <noah@leadboat.com> wrote:
>
> On Mon, Apr 15, 2024 at 04:12:38PM +0700, John Naylor wrote:
> > - Some paths for single-value leaves are not covered:
> >
> > https://anarazel.de/postgres/cov/16-vs-HEAD-2024-04-14/src/include/lib/radixtree.h.gcov.html#L904
> > https://anarazel.de/postgres/cov/16-vs-HEAD-2024-04-14/src/include/lib/radixtree.h.gcov.html#L954
> > https://anarazel.de/postgres/cov/16-vs-HEAD-2024-04-14/src/include/lib/radixtree.h.gcov.html#L2606
> >
> > However, these paths do get regression test coverage on 32-bit
> > machines. 64-bit builds only have leaves in the TID store, which
> > doesn't (currently) delete entries, and doesn't instantiate the tree
> > with the debug option.
> >
> > - In RT_SET "if (found)" is not covered:
> >
> > https://anarazel.de/postgres/cov/16-vs-HEAD-2024-04-14/src/include/lib/radixtree.h.gcov.html#L1768
> >
> > That's because we don't yet have code that replaces an existing value
> > with a value of a different length.
>
> I saw a SIGSEGV there when using tidstore to write a fix for something else.
> Patch attached.

Great find, thank you for the patch!

The fix looks good to me. I think we can improve regression tests for
better coverage. In TidStore on a 64-bit machine, we can store 3
offsets in the header and these values are embedded to the leaf page.
With more than 3 offsets, the value size becomes more than 16 bytes
and a single value leaf. Therefore, if we can add the test with the
array[1,2,3,4,100], we can cover the case of replacing a single-value
leaf with a different size new single-value leaf. Now we add 9 pairs
of do_gset_block_offset() and check_set_block_offsets(). If these are
annoying, we can remove the cases of array[1] and array[1,2].

I've attached a new patch. In addition to the new test case I
mentioned, I've added some new comments and removed an unnecessary
added line in test_tidstore.sql.

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