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: 2024-03-21T07:35:08Z
Lists: pgsql-hackers 
On Thu, Mar 21, 2024 at 1:11 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:

> Or we can have a new function for dsa.c to set the initial and max
> segment size (or either one) to the existing DSA area so that
> TidStoreCreate() can specify them at creation.

I didn't like this very much, because it's splitting an operation
across an API boundary. The caller already has all the information it
needs when it creates the DSA. Straw man proposal: it could do the
same for local memory, then they'd be more similar. But if we made
local contexts the responsibility of the caller, that would cause
duplication between creating and resetting.

> In shared TidStore
> cases, since all memory required by shared radix tree is allocated in
> the passed-in DSA area and the memory usage is the total segment size
> allocated in the DSA area

...plus apparently some overhead, I just found out today, but that's
beside the point.

On Thu, Mar 21, 2024 at 2:02 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> Yet another idea is that TidStore creates its own DSA area in
> TidStoreCreate(). That is, In TidStoreCreate() we create a DSA area
> (using dsa_create()) and pass it to RT_CREATE(). Also, we need a new
> API to get the DSA area. The caller (e.g. parallel vacuum) gets the
> dsa_handle of the DSA and stores it in the shared memory (e.g. in
> PVShared). TidStoreAttach() will take two arguments: dsa_handle for
> the DSA area and dsa_pointer for the shared radix tree. This idea
> still requires controlling min/max segment sizes since dsa_create()
> uses the 1MB as the initial segment size. But the TidStoreCreate()
> would be more user friendly.

This seems like an overall simplification, aside from future size
configuration, so +1 to continue looking into this. If we go this
route, I'd like to avoid a boolean parameter and cleanly separate
TidStoreCreateLocal() and TidStoreCreateShared(). Every operation
after that can introspect, but it's a bit awkward to force these cases
into the same function. It always was a little bit, but this change
makes it more so.

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