Horton

Re: AIO v2.4

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: pgsql-hackers@postgresql.org
Cc: Thomas Munro <thomas.munro@gmail.com>, pgsql-hackers@postgresql.org, Heikki Linnakangas <hlinnaka@iki.fi>, Noah Misch <noah@leadboat.com>, Robert Haas <robertmhaas@gmail.com>, Jakub Wartak <jakub.wartak@enterprisedb.com>
Date: 2025-02-19T19:10:44Z
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 aio: Fix reference to outdated name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

Attachments

Hi,

Attached is v2.4 of the AIO patchset.

Changes:

- Introduce "batchmode", while not in batchmode, IOs get submitted immediately.

  Thomas didn't like how this worked previously, and while this was a
  surprisingly large amount of work, I agree that it looks better now.

  I vaccilated a bunch on the naming. For now it's

  extern void pgaio_enter_batchmode(void);
  extern void pgaio_exit_batchmode(void);

  I did adjust the README and wrote a reasonably long comment above enter:
  https://github.com/anarazel/postgres/blob/a324870186ddff9a31b10472b790eb4e744c40b3/src/backend/storage/aio/aio.c#L931-L960


- Batchmode needs to be exited in case of errors, for that

  - a new pgaio_after_error() call has been added to all the relevant places

  - xact.c calls to aio have been (re-)added to check that there are no
    in-progress batches / unsubmitted IOs at the end of a transaction.

    Before that I had just removed at-eoxact "callbacks" :)

    This checking has holes though:
    https://postgr.es/m/upkkyhyuv6ultnejrutqcu657atw22kluh4lt2oidzxxtjqux3%40a4hdzamh4wzo

    Because this only means that we will not detect all buggy code, rather
    than misbehaving for correct code, I think this may be ok for now.


- Renamed aio_init.h to aio_subsys.h

  The newly added pgaio_after_error() calls would have required including
  aio.h in a good bit more places that won't themselves issue AIO. That seemed
  wrong.  There already was a aio_init.h to avoid needing to include aio.h in
  places like ipci.c, but it seemed wrong to put pgaio_after_error() in
  aio_init.h.  So I renamed it to aio_subsys.h - not sure that's the best
  name, but I can live with it.


- Now that Thomas submitted the necessary read_stream.c improvements, the
  prior big TODO about one StartReadBuffers() call needing to start many IOs
  has been addressed.

  Thomas' thread: https://postgr.es/m/CA%2BhUKGK_%3D4CVmMHvsHjOVrK6t4F%3DLBpFzsrr3R%2BaJYN8kcTfWg%40mail.gmail.com

  For now I've also included Thomas patches in my queue, but they should get
  pushed independently.  Review comments specific to those patches probably
  are better put on the other thread.

  Thomas' patches also fix several issues that were addressed in my WIP
  adjustments to read_stream.c.  There are a few left, but it does look
  better.

  The included commits are 0003-0008.


- I rewrote the tests into a tap test. That was exceedingly painful. Partially
  due to tap infrastructure bugs on windows that would sometimes cause
  inscrutable failures, see
  https://www.postgresql.org/message-id/wmovm6xcbwh7twdtymxuboaoarbvwj2haasd3sikzlb3dkgz76%40n45rzycluzft

  I just pushed that fix earlier today.


- Added docs for new GUCs, moved them to a more appropriate section

  See also https://postgr.es/m/x3tlw2jk5gm3r3mv47hwrshffyw7halpczkfbk3peksxds7bvc%40lguk43z3bsyq


- If IO workers fail to reopen the file for an IO, the IO is now marked as
  failed. Previously we'd just hang.

  To test this I added an injection point that triggers the failure. I don't
  know how else this could be tested.


- Added liburing dependency build documentation


- Added check hook to ensure io_max_concurrency = isn't set to 0 (-1 is for
  auto-config)


- Fixed that with io_method == sync we'd issue fadvise calls when not
  appropriate, that was a consequence of my hacky read_stream.c changes.


- Renamed some the aio<->bufmgr.c interface functions. Don't think they're
  quite perfect, but they're in later patches, so I don't want to focus too
  much on them rn.


- Comment improvements etc.


- Got rid of an unused wait event and renamed other wait events to make more
  sense.


- Previously the injection points were added as part of the test patch, I now
  moved them into the commits adding the code being tested. Was too annoying
  to edit otherwise.


Todo:

- there's a decent amount of FIXMEs in later commits related to ereport(LOG)s
  needing relpath() while in a critical section.  I did propose a solution to
  that yesterday:

  https://postgr.es/m/h3a7ftrxypgxbw6ukcrrkspjon5dlninedwb5udkrase3rgqvn%403cokde6btlrl

- A few more corner case tests for the interaction of multiple backends trying
  to do IO on overlapping buffers would be good.

- Our temp table test coverage is atrociously bad


Questions:

- The test module requires StartBufferIO() to be visible outside of bufmgr.c -
  I think that's ok, would be good to know if others agree.


I'm planning to push the first two commits soon, I think they're ok on their
own, even if nothing else were to go in.


Greetings,

Andres Freund