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: 2025-03-23T02:09:55Z
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 aio: Fix reference to outdated name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 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

Apart from some isolated cosmetic points, this is ready to commit:

> +			ereport(ERROR,
> +					errcode(err),
> +					errmsg("io_uring_queue_init failed: %m"),
> +					hint != NULL ? errhint("%s", hint) : 0);

https://www.postgresql.org/docs/current/error-style-guide.html gives the example:

BAD:    open() failed: %m
BETTER: could not open file %s: %m

Hence, this errmsg should change, perhaps to:
"could not setup io_uring queues: %m".

> +		pgaio_debug_io(DEBUG3, ioh,
> +					   "wait_one io_gen: %llu, ref_gen: %llu, cycle %d",
> +					   (long long unsigned) ref_generation,
> +					   (long long unsigned) ioh->generation,

In the message string, io_gen appears before ref_gen.  In the subsequent args,
the order is swapped relative to the message string.

> --- 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."

> --- 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.

> Subject: [PATCH v2.11 06/27] aio: Implement support for reads in smgr/md/fd

(Still reviewing this one.)