Horton

Re: AIO v2.2

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: pgsql-hackers@postgresql.org
Date: 2025-01-07T16:32:10Z
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 aio: Fix reference to outdated name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 2025-01-07 18:08:51 +0200, Heikki Linnakangas wrote:
> On LWLockDisown():
> 
> > +/*
> > + * Stop treating lock as held by current backend.
> > + *
> > + * After calling this function it's the callers responsibility to ensure that
> > + * the lock gets released, even in case of an error. This only is desirable if
> > + * the lock is going to be released in a different process than the process
> > + * that acquired it.
> > + *
> > + * Returns the mode in which the lock was held by the current backend.
> 
> Returning the lock mode feels a bit ad hoc..

It seemed useful to me, that way callers could verify that the released lock
level is actually what it expected. What do we gain by hiding this information
anyway?

Orthogonal: I think it was a mistake that LWLockRelease() didn't require the
to-be-releaased lock mode to be passed in...


> > + * NB: This will leave lock->owner pointing to the current backend (if
> > + * LOCK_DEBUG is set). We could add a separate flag indicating that, but it
> > + * doesn't really seem worth it.
> 
> Hmm. I won't insist, but I feel it probably would be worth it. This is only
> in LOCK_DEBUG mode so there's no performance penalty in non-debug builds,
> and when you do compile with LOCK_DEBUG you probably appreciate any extra
> information.

I actually thought it'd be more useful if it stays pointing to the 'original
owner'.

When you say "it" would be worth it, you mean resetting owner, or adding a
flag indicating that it's a disowned lock?



> > + * NB: This does not call RESUME_INTERRUPTS(), but leaves that responsibility
> > + * of the caller.
> > + */
> 
> That feels weird. The only caller outside lwlock.c does call
> RESUME_INTERRUPTS() immediately.

Yea, I didn't feel happy with it either. It just seemed that the cure (a
separate function, or a parameter indicating whether interrupts should be
resumed) was as bad as the disease.


> Perhaps it'd make for a better external interface if LWLockDisown() did call
> RESUME_INTERRUPTS(), and there was a separate internal version that didn't.

Hm, that seems more complicated than it's worth.  I'd either leave it as-is,
or add a parameter to LWLockDisown to indicate if interrupts should be
resumed.


> And it might make more sense for the external version to return 'void' while
> we're at it. Returning a value that the caller ignores is harmless, of
> course, but it feels a bit weird. It makes you wonder what you're supposed
> to do with it.

This one I disagree with, I think it makes a lot of sense to return the lock
mode of the lock you just disowned.

Doubtful it matters, but the compiler can trivially optimize that out for the
lwlock.c callers.


> > +	{
> > +		{"io_method", PGC_POSTMASTER, RESOURCES_MEM,
> > +			gettext_noop("Selects the method of asynchronous I/O to use."),
> > +			NULL
> > +		},
> > +		&io_method,
> > +		DEFAULT_IO_METHOD, io_method_options,
> > +		NULL, assign_io_method, NULL
> > +	},
> > +
> 
> The description is a bit funny because synchronous I/O is one of the
> possible methods.

Hah.  How about:

"Selects the method of, potentially asynchronous, IO execution."?

Greetings,

Andres Freund