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: John Naylor <johncnaylorls@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: 2024-03-21T07:02:05Z
Lists: pgsql-hackers

Attachments

On Thu, Mar 21, 2024 at 3:10 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Thu, Mar 21, 2024 at 12:40 PM John Naylor <johncnaylorls@gmail.com> wrote:
> >
> > 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.
>
> 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. 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, the user will have to prepare a DSA area
> only for the shared tidstore. So we might be able to expect that the
> DSA passed-in to TidStoreCreate() is empty and its segment sizes can
> be adjustable.

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.

I've attached a PoC patch for discussion.

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