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Re: Buffer locking is special (hints, checksums, AIO writes)

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: Kirill Reshke <reshkekirill@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Matthias van de Meent <boekewurm+postgres@gmail.com>, pgsql-hackers@postgresql.org, Thomas Munro <thomas.munro@gmail.com>, Noah Misch <noah@leadboat.com>, Robert Haas <robertmhaas@gmail.com>, Michael Paquier <michael.paquier@gmail.com>
Date: 2026-01-14T00:49:00Z
Lists: pgsql-hackers 
Hi,

On 2026-01-13 10:05:02 -0500, Melanie Plageman wrote:
> On Mon, Jan 12, 2026 at 7:33 PM Andres Freund <andres@anarazel.de> wrote:
> >
> > - added a commit that renames ResOwnerReleaseBufferPin to
> >   ResOwnerReleaseBuffer (et al), as it now also releases content locks if held
> >
> >   I kept this separate as I'm not yet sure about the new name, partially due
> >   to there also being a "buffer io" resowner.  I tried "buffer ownership" for
> >   the resowner that tracks pins and locks, but that was long and not clearly
> >   better.
> 
> I didn't look at the patch but I strongly agree that
> ResOwnerReleaseBufferPin() should not also release locks, so it should
> have a new name.

OK.

> Ironic that ResOwnerReleaseBufferIO() releases pins and not locks.

Not sure I follow? I don't think it releases pins? And why should it release
locks?


> What about ResOwnerReleaseBufferClaim() or
> ResOwnerReleaseBufferAccess() or ResOwnerReleaseBufferHold()?

I'm inclined to go with just ResOwnerReleaseBuffer() at the moment. Buffer IO
kind of is a subsidiary thing, and it requires holding a pin as well, so it
doesn't feel too wrong.

I also wonder if we could merge BufferIO into the private refcount
infrastructure, similar to how the patches store the lockmode in the private
refcount.  The separate resowner acquisition does show up in profiles when
reading from the kernel page cache, so that'd be a nice (but small)
improvement.

Greetings,

Andres Freund

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. bufmgr: Fix ordering of checks in PinBuffer()

  2. Use UnlockReleaseBuffer() in more places

  3. bufmgr: Make UnlockReleaseBuffer() more efficient

  4. bufmgr: Don't copy pages while writing out

  5. Fix use of wrong variable in _hash_kill_items()

  6. Fix bug due to confusion about what IsMVCCSnapshot means

  7. bufmgr: Switch to standard order in MarkBufferDirtyHint()

  8. bufmgr: Remove the, now obsolete, BM_JUST_DIRTIED

  9. Require share-exclusive lock to set hint bits and to flush

  10. heapam: Don't mimic MarkBufferDirtyHint() in inplace updates

  11. bufmgr: Allow conditionally locking of already locked buffer

  12. bufmgr: Avoid spurious compiler warning after fcb9c977aa5

  13. lwlock: Remove ForEachLWLockHeldByMe

  14. lwlock: Remove support for disowned lwlwocks

  15. bufmgr: Implement buffer content locks independently of lwlocks

  16. bufmgr: Change BufferDesc.state to be a 64-bit atomic

  17. lwlock: Improve local variable name

  18. lwlock: Invert meaning of LW_FLAG_RELEASE_OK

  19. bufmgr: Make definitions related to buffer descriptor easier to modify

  20. heapam: Add batch mode mvcc check and use it in page mode

  21. freespace: Don't modify page without any lock

  22. heapam: Move logic to handle HEAP_MOVED into a helper function

  23. bufmgr: Optimize & harmonize LockBufHdr(), LWLockWaitListLock()

  24. bufmgr: Add one-entry cache for private refcount

  25. bufmgr: Separate keys for private refcount infrastructure

  26. Add pg_atomic_unlocked_write_u64

  27. Rename BUFFERPIN wait event class to BUFFER

  28. bufmgr: Turn BUFFER_LOCK_* into an enum

  29. lwlock: Fix, currently harmless, bug in LWLockWakeup()

  30. bufmgr: Use atomic sub for unpinning buffers

  31. bufmgr: Allow some buffer state modifications while holding header lock

  32. bufmgr: Fix valgrind checking for buffers pinned in StrategyGetBuffer()

  33. bufmgr: Don't lock buffer header in StrategyGetBuffer()

  34. bufmgr: fewer calls to BufferDescriptorGetContentLock

  35. bufmgr: Fix signedness of mask variable in BufferSync()

  36. bufmgr: Introduce FlushUnlockedBuffer

  37. Improve ReadRecentBuffer() scalability