Horton

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: Peter Geoghegan <pg@bowt.ie>
Cc: Melanie Plageman <melanieplageman@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, pgsql-hackers@postgresql.org, Thomas Munro <thomas.munro@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Noah Misch <noah@leadboat.com>, Robert Haas <robertmhaas@gmail.com>, Michael Paquier <michael.paquier@gmail.com>
Date: 2025-12-03T01:18:38Z
Lists: pgsql-hackers

Commits

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

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

  2. lwlock: Remove ForEachLWLockHeldByMe

  3. bufmgr: Implement buffer content locks independently of lwlocks

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

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

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

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

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

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

  10. bufmgr: Separate keys for private refcount infrastructure

  11. Add pg_atomic_unlocked_write_u64

  12. Rename BUFFERPIN wait event class to BUFFER

  13. bufmgr: Turn BUFFER_LOCK_* into an enum

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

  15. bufmgr: Use atomic sub for unpinning buffers

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

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

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

  19. bufmgr: fewer calls to BufferDescriptorGetContentLock

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

  21. bufmgr: Introduce FlushUnlockedBuffer

  22. Improve ReadRecentBuffer() scalability

Hi,

On 2025-12-02 20:12:14 -0500, Peter Geoghegan wrote:
> On Tue, Dec 2, 2025 at 7:47 PM Andres Freund <andres@anarazel.de> wrote:
> > On 2025-11-25 11:54:00 -0500, Andres Freund wrote:
> > > Thanks a lot for that detailed review!  A few questions and comments, before I
> > > try to address the comments in the next version.
> >
> > Here's that new new version, with the following changes
> 
> _bt_check_unique will hold an exclusive buffer lock on the page being
> LP_DEAD-set in the vast majority of cases. Should we expect your
> changes to have no effect at all in that common case?

If we already have an exclusive lock, BufferBeginSetHintBits() will quickly
return true and won't ever return false.


> The BTP_HAS_GARBAGE flag is deprecated these days; we basically don't
> use it anymore. How much value might there be in avoiding setting
> BTP_HAS_GARBAGE as a way of being able to use BufferSetHintBits16 more
> often in nbtree?

None of the MarkBufferDirtyHint() cases in nbtree that had to be modified
looked like they would benefit from BufferSetHintBits16(), since they will
typically modify the page multiple times.  But maybe I'm just misunderstanding
what you mean?

Greetings,

Andres Freund