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: Andres Freund <andres@anarazel.de>
Cc: John Naylor <john.naylor@enterprisedb.com>, Nathan Bossart <nathandbossart@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2022-11-30T16:08:27Z
Lists: pgsql-hackers 
On Wed, Nov 23, 2022 at 2:10 AM Andres Freund <andres@anarazel.de> wrote:
>
> On 2022-11-21 17:06:56 +0900, Masahiko Sawada wrote:
> > Sure. I've attached the v10 patches. 0004 is the pure refactoring
> > patch and 0005 patch introduces the pointer tagging.
>
> This failed on cfbot, with som many crashes that the VM ran out of disk for
> core dumps. During testing with 32bit, so there's probably something broken
> around that.
>
> https://cirrus-ci.com/task/4635135954386944
>
> A failure is e.g. at: https://api.cirrus-ci.com/v1/artifact/task/4635135954386944/testrun/build-32/testrun/adminpack/regress/log/initdb.log
>
> performing post-bootstrap initialization ... ../src/backend/lib/radixtree.c:1696:21: runtime error: member access within misaligned address 0x590faf74 for type 'struct radix_tree_control', which requires 8 byte alignment
> 0x590faf74: note: pointer points here
>   90 11 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
>               ^

radix_tree_control struct has two pg_atomic_uint64 variables, and the
assertion check in pg_atomic_init_u64() failed:

static inline void
pg_atomic_init_u64(volatile pg_atomic_uint64 *ptr, uint64 val)
{
    /*
     * Can't necessarily enforce alignment - and don't need it - when using
     * the spinlock based fallback implementation. Therefore only assert when
     * not using it.
     */
#ifndef PG_HAVE_ATOMIC_U64_SIMULATION
    AssertPointerAlignment(ptr, 8);
#endif
    pg_atomic_init_u64_impl(ptr, val);
}

I've investigated this issue and have a question about using atomic
variables on palloc'ed memory. In non-parallel vacuum cases,
radix_tree_control is allocated via aset.c. IIUC in 32-bit machines,
the memory allocated by aset.c is 4-bytes aligned so these atomic
variables are not always 8-bytes aligned. Is there any way to enforce
8-bytes aligned memory allocations in 32-bit machines?

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