Horton

Re: [PoC] Improve dead tuple storage for lazy vacuum

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-07-19T23:49:15Z
Lists: pgsql-hackers

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Hi,

On 2021-07-19 15:20:54 +0900, Masahiko Sawada wrote:
> BTW is the implementation of the radix tree approach available
> somewhere? If so I'd like to experiment with that too.
>
> >
> > I have toyed with implementing adaptively large radix nodes like
> > proposed in https://db.in.tum.de/~leis/papers/ART.pdf - but haven't
> > gotten it quite working.
>
> That seems promising approach.

I've since implemented some, but not all of the ideas of that paper
(adaptive node sizes, but not the tree compression pieces).

E.g. for

select prepare(
1000000, -- max block
20, -- # of dead tuples per page
10, -- dead tuples interval within a page
1 -- page inteval
);
        attach  size    shuffled	ordered
array    69 ms  120 MB  84.87 s          8.66 s
intset  173 ms   65 MB  68.82 s         11.75 s
rtbm    201 ms   67 MB  11.54 s          1.35 s
tbm     232 ms  100 MB   8.33 s          1.26 s
vtbm    162 ms   58 MB  10.01 s          1.22 s
radix    88 ms   42 MB  11.49 s          1.67 s

and for
select prepare(
1000000, -- max block
10, -- # of dead tuples per page
1, -- dead tuples interval within a page
1 -- page inteval
);

        attach  size    shuffled	ordered
array    24 ms   60MB   3.74s            1.02 s
intset   97 ms   49MB   3.14s            0.75 s
rtbm    138 ms   36MB   0.41s            0.14 s
tbm     198 ms  101MB   0.41s            0.14 s
vtbm    118 ms   27MB   0.39s            0.12 s
radix    33 ms   10MB   0.28s            0.10 s

(this is an almost unfairly good case for radix)

Running out of time to format the results of the other testcases before
I have to run, unfortunately. radix uses 42MB both in test case 3 and
4.


The radix tree code isn't good right now. A ridiculous amount of
duplication etc. The naming clearly shows its origins from a buffer
mapping radix tree...


Currently in a bunch of the cases 20% of the time is spent in
radix_reaped(). If I move that into radix.c and for bfm_lookup() to be
inlined, I get reduced overhead. rbtm for example essentially already
does that, because it does splitting of ItemPointer in rtbm.c.


I've attached my current patches against your tree.

Greetings,

Andres Freund

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