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>, Jelte Fennema-Nio <postgres@jeltef.nl>, Antonin Houska <ah@cybertec.at>
Date: 2025-04-07T19:24:42Z
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 aio: Fix reference to outdated name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 2025-04-05 06:43:52 -0700, Noah Misch wrote:
> Yeah.  Maybe this (untested):

Something like that works. I adopted your formulation of this, mine was in
GetLocalVictimBuffer(), which seems slightly less future proof.


> > > If that's right, it would still be nice to reach the right
> > > VALGRIND_MAKE_MEM_DEFINED() without involving bufmgr.
> >
> > I think that would be possible if we didn't do VALGRIND_MAKE_MEM_NOACCESS() in
> > UnpinBuffer()/UnpinLocalBuffer(). But with that I don't see how we can avoid
> > needing to remark the region as accessible?
>
> Yes, it's not that we should remove VALGRIND_MAKE_MEM_DEFINED() from bufmgr.
> I was trying to think about future AIO callers (e.g. RelationCopyStorage())
> and how they'd want things to work.

Ah, I now understand what you mean.  I'm inclined to leave that out for now,
we can do that later. I spent a bit of time experimenting with going bigger,
but I think it's important to get skink a bit less red.


> That said, perhaps we should just omit the io_uring-level Valgrind calls and
> delegate the problem to higher layers until there's a concrete use case:

Yes, I think that's the right answer for now. Applied your suggested comment.


I looked for a good place to add a comment to method_io_uring.c, but couldn't
really come up with anything convincing.  Then I thought the
 * "Start" routines for individual IO operations
comment in aio_io.c might be a good place, but also failed to come up with
anything particularly convincing.


> > > - A complete_local callback solves those problems.  However, if the
> > >   AIO-defining subxact aborted, then we shouldn't set DEFINED at all, since
> > >   the buffer mapping may have changed by the time of complete_local.
> >
> > I don't think that is possible, due to the aio subsystem owned pin?
>
> We currently drop the shared buffer AIO subsystem pin in complete_shared
> (buffer_readv_complete_one() -> TerminateBufferIO()).  I was trying to say
> that if we put a VALGRIND_MAKE_MEM_DEFINED in complete_local without changing
> anything else, it would have this problem.

Ah, yes, I see what you mean.


> We probably wouldn't want to move the shared buffer pin drop to
> complete_local without a strong reason.

Agreed.


> > I think the point about non-aio uses is a fair one, but I don't quite know how
> > to best solve it right now, due to the local buffer issue you mentioned. I'd
> > guess that we'd best put it somewhere
> > a) in pgaio_io_process_completion(), if definer==completor || !PGAIO_HF_REFERENCES_LOCAL
> > b) pgaio_io_call_complete_local(), just before calling
> >    pgaio_io_call_complete_local() if PGAIO_HF_REFERENCES_LOCAL
>
> I think that would do nothing wrong today, but it uses
> !PGAIO_HF_REFERENCES_LOCAL as a proxy for "target memory is already DEFINED,
> or a higher layer will make it DEFINED".  While !PGAIO_HF_REFERENCES_LOCAL
> does imply that today, I think that's a bufmgr-specific conclusion.  I have no
> particular reason to expect that to hold for future AIO use cases.  As above,
> I'd be inclined to omit the io_uring-level Valgrind calls until we have a
> concrete use case to drive their design.  How do you see it?

Yea, I'm not sure either.  I think we'll best wait until we have non-bufmgr
AIO to address all this. That'll make it easier to shake out.



I think eventually we should do an explicit
- VALGRIND_CHECK_MEM_IS_ADDRESSABLE() in pgaio_io_start_readv

- VALGRIND_CHECK_MEM_IS_DEFINED() in pgaio_io_start_writev

- VALGRIND_MAKE_MEM_DEFINED() in when a READV completes, although some of the
  details of when/where to do that aren't entirely clear to me yet. I suspect
  we might have to do it in pgaio_io_start_readv(), because it's harder to
  reliably do it later


I've pushed the patches. Thanks for the discussion, somehow the mix of shared
memory with valgrind tracking accessibility/definedness in a process local
manner is somewhat mindbending.

Greetings,

Andres Freund