Horton

Re: AIO v2.5

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Andres Freund <andres@anarazel.de>
Cc: Antonin Houska <ah@cybertec.at>, 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>, Jelte Fennema-Nio <postgres@jeltef.nl>
Date: 2025-03-23T16:32:48Z
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 aio: Fix reference to outdated name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

On Sun, Mar 23, 2025 at 11:57:48AM -0400, Andres Freund wrote:
> On 2025-03-22 19:09:55 -0700, Noah Misch wrote:
> > On Thu, Mar 20, 2025 at 09:58:37PM -0400, Andres Freund wrote:
> > > Attached v2.11
> >
> > > Subject: [PATCH v2.11 05/27] aio: Add io_method=io_uring

> > > --- a/src/backend/utils/activity/wait_event_names.txt
> > > +++ b/src/backend/utils/activity/wait_event_names.txt
> > > @@ -192,6 +192,8 @@ ABI_compatibility:
> > >
> > >  Section: ClassName - WaitEventIO
> > >
> > > +AIO_IO_URING_SUBMIT	"Waiting for IO submission via io_uring."
> > > +AIO_IO_URING_COMPLETION	"Waiting for IO completion via io_uring."
> > >  AIO_IO_COMPLETION	"Waiting for IO completion."
> >
> > I'm wondering if there's an opportunity to enrich the last two wait event
> > names and/or descriptions.  The current descriptions suggest to me more
> > similarity than is actually there.  Inputs to the decision:
> >
> > - AIO_IO_COMPLETION waits for an IO in PGAIO_HS_DEFINED, PGAIO_HS_STAGED, or
> >   PGAIO_HS_COMPLETED_IO to reach PGAIO_HS_COMPLETED_SHARED.  The three
> >   starting states are the states where some other backend owns the next
> >   action, so the current backend can only wait to be signaled.
> >
> > - AIO_IO_URING_COMPLETION waits for the kernel to do enough so we can move
> >   from PGAIO_HS_SUBMITTED to PGAIO_HS_COMPLETED_IO.
> >
> > Possible names and descriptions, based on PgAioHandleState enum names and
> > comments:
> >
> > AIO_IO_URING_COMPLETED_IO	"Waiting for IO result via io_uring."
> > AIO_COMPLETED_SHARED	"Waiting for IO shared completion callback."
> >
> > If "shared completion callback" is too internals-focused, perhaps this:
> >
> > AIO_IO_URING_COMPLETED_IO	"Waiting for IO result via io_uring."
> > AIO_COMPLETED_SHARED	"Waiting for IO completion to update shared memory."
> 
> Hm, right now AIO_IO_COMPLETION also covers the actual "raw" execution of the
> IO with io_method=worker/sync.

Right, it could start with the IO in PGAIO_HS_DEFINED and end with the IO in
PGAIO_HS_COMPLETED_SHARED.  So another part of the wait may be the definer
doing work before exiting batch mode.

> For that AIO_COMPLETED_SHARED would be
> inappropriate.

The concept I had in mind was "waiting to reach PGAIO_HS_COMPLETED_SHARED,
whatever obstacles that involves".

Another candidate description string:

AIO_COMPLETED_SHARED	"Waiting for another process to complete IO."

> We could use a different wait event if wait for an IO via CV in
> PGAIO_HS_SUBMITTED, with a small refactoring of pgaio_io_wait().  But I'm not
> sure that would get you that far - we don't broadcast the CV when
> transitioning from PGAIO_HS_SUBMITTED -> PGAIO_HS_COMPLETED_IO, so the wait
> event would stay the same, now wrong, wait event until the shared callback
> completes. Obviously waking everyone up just so they can use a differen wait
> event doesn't make sense.

Agreed.  The mapping of code ranges to wait events seems fine to me.  I'm mainly
trying to optimize the wait event description strings to fit those code ranges.

> A more minimal change would be to narrow AIO_IO_URING_COMPLETION to
> "execution" or something like that, to hint at a separation between the raw IO
> being completed and the IO, including the callbacks completing.

Yes, that would work for me.

> > > --- a/doc/src/sgml/config.sgml
> > > +++ b/doc/src/sgml/config.sgml
> > > @@ -2710,6 +2710,12 @@ include_dir 'conf.d'
> > >              <literal>worker</literal> (execute asynchronous I/O using worker processes)
> > >             </para>
> > >            </listitem>
> > > +          <listitem>
> > > +           <para>
> > > +            <literal>io_uring</literal> (execute asynchronous I/O using
> > > +            io_uring, if available)
> >
> > I feel the "if available" doesn't quite fit, since we'll fail if unavailable.
> > Maybe just "(execute asynchronous I/O using Linux io_uring)" with "Linux"
> > there to reduce surprise on other platforms.
> 
> You're right, the if available can be misunderstood. But not mentioning that
> it's an optional dependency seems odd too. What about something like
> 
>            <para>
>             <literal>io_uring</literal> (execute asynchronous I/O using
>             io_uring, requires postgres to have been built with
>             <link linkend="configure-option-with-liburing"><option>--with-liburing</option></link> /
>             <link linkend="configure-with-liburing-meson"><option>-Dliburing</option></link>)
>            </para>

I'd change s/postgres to have been built/a build with/ since the SGML docs
don't use the term "postgres" that way.  Otherwise, that works for me.

> Should the docs for --with-liburing/-Dliburing mention it's linux only? We
> don't seem to do that for things like systemd (linux), selinux (linux) and
> only kinda for bonjour (macos).

No need, I think.