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base repository: postgresql-cfbot/postgresql
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head repository: postgresql-cfbot/postgresql
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compare: cf/5620
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  • 4 commits
  • 5 files changed
  • 2 contributors

Commits on Apr 1, 2025

  1. Improve acounting for memory used by shared hash tables 

    pg_shmem_allocations tracks the memory allocated by ShmemInitStruct(),
but for shared hash tables that covered only the header and hash
directory.  The remaining parts (segments and buckets) were allocated
later using ShmemAlloc(), which does not update the shmem accounting.
Thus, these allocations were not shown in pg_shmem_allocations.

This commit improves the situation by allocating all the hash table
parts at once, using a single ShmemInitStruct() call. This way the
ShmemIndex entries (and thus pg_shmem_allocations) better reflect the
proper size of the hash table.

This affects allocations for private (non-shared) hash tables too, as
the hash_create() code is shared. For non-shared tables this however
makes no practical difference.

This changes the alignment a bit. ShmemAlloc() aligns the chunks using
CACHELINEALIGN(), which means some parts (header, directory, segments)
were aligned this way. Allocating all parts as a single chunks removes
this (implicit) alignment. We've considered adding explicit alignment,
but we've decided not to - it seems to be merely a coincidence due to
using the ShmemAlloc() API, not due to necessity.

Author: Rahila Syed <[email protected]>
Reviewed-by: Andres Freund <[email protected]>
Reviewed-by: Nazir Bilal Yavuz <[email protected]>
Reviewed-by: Tomas Vondra <[email protected]>
Discussion: https://postgr.es/m/CAH2L28vHzRankszhqz7deXURxKncxfirnuW68zD7+hVAqaS5GQ@mail.gmail.com
    @Rahila
    Rahila authored and Commitfest Bot committed Apr 1, 2025
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  2. Improve accounting for PredXactList, RWConflictPool and PGPROC 

    Various places allocated shared memory by first allocating a small chunk
using ShmemInitStruct(), followed by ShmemAlloc() calls to allocate more
memory. Unfortunately, ShmemAlloc() does not update ShmemIndex, so this
affected pg_shmem_allocations - it only shown the initial chunk.

This commit modifies the following allocations, to allocate everything
as a single chunk, and then split it internally.

- PredXactList
- RWConflictPool
- PGPROC structures
- Fast-Path lock arrays

Author: Rahila Syed <[email protected]>
Reviewed-by: Andres Freund <[email protected]>
Reviewed-by: Nazir Bilal Yavuz <[email protected]>
Reviewed-by: Tomas Vondra <[email protected]>
Discussion: https://postgr.es/m/CAH2L28vHzRankszhqz7deXURxKncxfirnuW68zD7+hVAqaS5GQ@mail.gmail.com
    @Rahila
    Rahila authored and Commitfest Bot committed Apr 1, 2025
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  3. Add cacheline padding between heavily accessed arrays

    @Rahila
    Rahila authored and Commitfest Bot committed Apr 1, 2025
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  4. [CF 5620] v9 - Improve monitoring of shared memory allocations 

    This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/5620

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/CAH2L28vaktm0UXw19y22w+DThcqV80-UKtVfMxPeVw8ro2yTDg@mail.gmail.com
Author(s): Rahila Syed
    Commitfest Bot committed Apr 1, 2025
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