Horton

Re: AIO v2.3

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Thomas Munro <thomas.munro@gmail.com>, pgsql-hackers@postgresql.org, Heikki Linnakangas <hlinnaka@iki.fi>, Noah Misch <noah@leadboat.com>, Jakub Wartak <jakub.wartak@enterprisedb.com>
Date: 2025-02-17T21:01:42Z
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 aio: Fix reference to outdated name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 2025-02-12 13:00:22 -0500, Robert Haas wrote:
> On Tue, Feb 11, 2025 at 4:43 PM Andres Freund <andres@anarazel.de> wrote:
> > One way we could avoid the need for a mechanism to reset-batch-in-progress
> > would be to make batch submission controlled by a flag on the IO. Something
> > like
> >     pgaio_io_set_flag(ioh, PGAIO_HF_BATCH_SUBMIT)
> >
> > IFF PGAIO_HF_BATCH_SUBMIT is set, the IOs would need to be explicitly
> > submitted using something like the existing
> >     pgaio_submit_staged();
> > (although renaming it to something with batch in the name might be
> > appropriate)
> >
> > That way there's no explicit "we are in a batch" state that needs to be reset
> > in case of errors.
> 
> I'll defer to Thomas or others on whether this is better or worse,
> because I don't know. It means that the individual I/Os have to know
> that they are in a batch, which isn't necessary with the begin/end
> batch interface. But if we're expecting that to happen in a pretty
> confined amount of code -- similar to WAL record construction -- then
> that might not be a problem anyway.
> 
> I think if you don't do this, I'd do (sub)xact callbacks rather than a
> resowner integration, unless you decide you want to support multiple
> concurrent batches. You don't really need or want to tie it to a
> resowner unless there are multiple objects each of which can have its
> own resources.

I have working code for that. There unfortunately is an annoying problem:

It afaict is not really possible to trigger a WARNING/ERRROR/Assert in xact
callbacks at the end of commands in an explicit transaction.  Consider
something like:

  BEGIN;
  SELECT start_but_not_end_aio_batch();

we would like to flag that the SELECT query started an AIO batch but didn't
end it. But at the momment there, afaict, is no proper way to do that, because
xact.c won't actually do much at the end of a command in a transaction block:

			/*
			 * This is the case when we have finished executing a command
			 * someplace within a transaction block.  We increment the command
			 * counter and return.
			 */
		case TBLOCK_INPROGRESS:
		case TBLOCK_IMPLICIT_INPROGRESS:
		case TBLOCK_SUBINPROGRESS:
			CommandCounterIncrement();
			break;

If one instead integrates with resowners, that kind of thing works, because
exec_simple_query() calls PortalDrop(), which in turn calls
ResourceOwnerRelease().


And we don't reliably warn at a later time. While xact.c integration triggers
a warning for:

  BEGIN;
  SELECT start_but_not_end_aio_batch();
  COMMIT;

as we'd still have the batch open at COMMIT, it wouldn't trigger for

  BEGIN;
  SELECT start_but_not_end_aio_batch();
  ROLLBACK;

as AbortTransaction() might be called in an error and therefore can't assume
that it's a problem for a batch to still be open.


I guess I could just put something alongside that CommandCounterIncrement()
call, but that doesn't seem right.  I guess putting it alongside the
ResourceOwnerRelease() in PortalDrop() is a bit less bad? But still doesn't
seem great.


Just using resowners doesn't seem right either, it's not really free to
register something with resowners, and for read intensive IO we can start a
*lot* of batches, so doing unnecessary work isn't great.

Greetings,

Andres Freund