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: 2024-03-01T04:15:05Z
Lists: pgsql-hackers 
I'm looking at RT_FREE_RECURSE again (only used for DSA memory), and
I'm not convinced it's freeing all the memory. It's been many months
since we discussed this last, but IIRC we cannot just tell DSA to free
all its segments, right? Is there currently anything preventing us
from destroying the whole DSA area at once?

+ /* The last level node has pointers to values */
+ if (shift == 0)
+ {
+   dsa_free(tree->dsa, ptr);
+   return;
+ }

IIUC, this doesn't actually free leaves, it only frees the last-level
node. And, this function is unaware of whether children could be
embedded values. I'm thinking we need to get rid of the above
pre-check and instead, each node kind to have something like (e.g.
node4):

RT_PTR_ALLOC child = n4->children[i];

if (shift > 0)
  RT_FREE_RECURSE(tree, child, shift - RT_SPAN);
else if (!RT_CHILDPTR_IS_VALUE(child))
  dsa_free(tree->dsa, child);

...or am I missing something?

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