Horton

Re: AIO v2.5

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Noah Misch <noah@leadboat.com>
Cc: pgsql-hackers@postgresql.org, Thomas Munro <thomas.munro@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Robert Haas <robertmhaas@gmail.com>, Jakub Wartak <jakub.wartak@enterprisedb.com>
Date: 2025-03-12T16:10:42Z
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. aio: Fix assertion, clarify README

  2. aio: Fix reference to outdated name

  3. aio: Fix possible state confusions due to interrupt processing

  4. aio: Improve debug logging around waiting for IOs

  5. aio: Fix crash potential for pg_aios views due to late state update

  6. Increase BAS_BULKREAD based on effective_io_concurrency

  7. localbuf: Add Valgrind buffer access instrumentation

  8. aio: Make AIO more compatible with valgrind

  9. aio: Avoid spurious coverity warning

  10. tests: Fix incompatibility of test_aio with *_FORCE_RELEASE

  11. tests: Cope with WARNINGs during failed CREATE DB on windows

  12. aio: Add errcontext for processing I/Os for another backend

  13. aio: Add README.md explaining higher level design

  14. aio: Minor comment improvements

  15. aio: Add test_aio module

  16. aio: Add pg_aios view

  17. docs: Add acronym and glossary entries for I/O and AIO

  18. Enable IO concurrency on all systems

  19. read_stream: Introduce and use optional batchmode support

  20. docs: Reframe track_io_timing related docs as wait time

  21. bufmgr: Use AIO in StartReadBuffers()

  22. bufmgr: Implement AIO read support

  23. aio: Add WARNING result status

  24. Let caller of PageIsVerified() control ignore_checksum_failure

  25. pgstat: Allow checksum errors to be reported in critical sections

  26. Add errhint_internal()

  27. localbuf: Track pincount in BufferDesc as well

  28. aio, bufmgr: Comment fixes/improvements

  29. Fix mis-attribution of checksum failure stats to the wrong database

  30. aio: Implement support for reads in smgr/md/fd

  31. aio: Add io_method=io_uring

  32. aio: Add liburing dependency

  33. aio: Rename pgaio_io_prep_* to pgaio_io_start_*

  34. aio: Pass result of local callbacks to ->report_return

  35. aio: Be more paranoid about interrupts

  36. Redefine max_files_per_process to control additionally opened files

  37. aio: Change prefix of PgAioResultStatus values to PGAIO_RS_

  38. bufmgr: Improve stats when a buffer is read in concurrently

  39. aio: Add io_method=worker

  40. aio: Infrastructure for io_method=worker

  41. aio: Add core asynchronous I/O infrastructure

  42. aio: Basic subsystem initialization

  43. tests: Expand temp table tests to some pin related matters

  44. localbuf: Introduce FlushLocalBuffer()

  45. localbuf: Introduce TerminateLocalBufferIO()

  46. localbuf: Fix dangerous coding pattern in GetLocalVictimBuffer()

  47. localbuf: Introduce StartLocalBufferIO()

  48. localbuf: Introduce InvalidateLocalBuffer()

  49. Allow lwlocks to be disowned

  50. Make jsonb casts to scalar types translate JSON null to SQL NULL.

  51. bufmgr/smgr: Don't cross segment boundaries in StartReadBuffers()

  52. Use aux process resource owner in walsender

  53. bufmgr: Return early in ScheduleBufferTagForWriteback() if fsync=off

Hi,

On 2025-03-11 19:55:35 -0400, Andres Freund wrote:
> On 2025-03-11 12:41:08 -0700, Noah Misch wrote:
> > On Mon, Sep 16, 2024 at 01:51:42PM -0400, Andres Freund wrote:
> > > On 2024-09-16 07:43:49 -0700, Noah Misch wrote:
> > > > For non-sync IO methods, I gather it's essential that a process other than the
> > > > IO definer be scanning for incomplete IOs and completing them.
> >
> > > > Otherwise, deadlocks like this would happen:
> > >
> > > > backend1 locks blk1 for non-IO reasons
> > > > backend2 locks blk2, starts AIO write
> > > > backend1 waits for lock on blk2 for non-IO reasons
> > > > backend2 waits for lock on blk1 for non-IO reasons
> > > >
> > > > If that's right, in worker mode, the IO worker resolves that deadlock.  What
> > > > resolves it under io_uring?  Another process that happens to do
> > > > pgaio_io_ref_wait() would dislodge things, but I didn't locate the code to
> > > > make that happen systematically.
> > >
> > > Yea, it's code that I haven't forward ported yet. I think basically
> > > LockBuffer[ForCleanup] ought to call pgaio_io_ref_wait() when it can't
> > > immediately acquire the lock and if the buffer has IO going on.
> >
> > I'm not finding that code in v2.6.  What function has it?
> 
> My local version now has it... Sorry, I was focusing on the earlier patches
> until now.

Looking more at my draft, I don't think it was race-free.  I had a race-free
way of doing it in the v1 patch (by making lwlocks extensible, so the check
for IO could happen between enqueueing on the lwlock wait queue and sleeping
on the semaphore), but that obviously requires that infrastructure.

I want to focus on reads for now, so I'll add FIXMEs to the relevant places in
the patch to support AIO writes and focus on the rest of the patch for now.

Greetings,

Andres Freund