Horton

Re: AIO v2.5

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Antonin Houska <ah@cybertec.at>
Cc: Noah Misch <noah@leadboat.com>, 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: 2025-03-14T19:43:15Z
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 aio: Fix reference to outdated name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,

On 2025-03-13 11:53:03 +0100, Antonin Houska wrote:
> Attached are a few proposals for minor comment fixes.

Thanks, applied.


> Besides that, it occurred to me when I was trying to get familiar with the
> patch set (respectable work, btw) that an additional Assert() statement could
> make sense:

Yea, it does. I added it to another place as well.


Attached is v2.8 with the following changes:

- I wasn't happy with the way StartReadBuffers(), WaitReadBuffers() and
  AsyncReadBuffers() interacted. The io_method=sync path in particular was too
  cute by half, calling WaitReadBuffers() from within WaitReadBuffers().

  I think the new state considerably better.

  Plenty other smaller changes as part of that. One worth calling out is that
  ReadBuffersCanStartIO() now submits staged IO before actually blocking. Not
  the prettiest code, but I think it's ok.


- Added a function to assert the sanitiy of a ReadBuffersOperation

  While doing the refactoring for the prior point, I temporarily had a bug
  that returned buffers for which IO wasn't actually performed. Surprisingly
  the only assertion that triggered was when that buffer was read again by
  another operation, because it had been marked dirty, despite never being
  valid.

  Now there's a function that can be used to check that the buffers referenced
  by a ReadBuffersOperation are in a sane state.

  I guess this could be committed independently, but it'd not be entirely
  trivial to extract, so I'm currently leaning against doing that.


- Previously VacuumCostActive accounting happened after IO completion. But
  that doesn't seem quite right, it'd allow to submit a lot of IO at
  once. It's now moved to AsyncReadBuffers()


- With io_method=sync or with worker and temp tables, smgrstartreadv() would
  actually execute the IO. But the time accounting was done entirely around
  pgaio_wref_wait(). Now it's done in both places.


- Rebased onto newer version of Thomas' read_stream.c changes

  With that newer version the integration with read stream for actually doing
  AIO is a bit simpler.  There's one FIXME in the patch, because I don't
  really understand what a comment is referring to.

  I also split out a more experimental patch to make more efficient use of
  batching in read stream, the heuristics are more complicated, and it works
  well enough without.


- I added a commit to clean up the buffer access accounting for the case that
  a buffer was read in concurrently. That IMO is somewhat bogus on master, and
  it seemed to get more bogus with AIO.


- Integrated Antonin Houska's fixes and Assert suggestion


- Added a patch to address the smgr.c/md.c interrupt issue (a problem in master), see
  https://postgr.es/m/3vae7l5ozvqtxmd7rr7zaeq3qkuipz365u3rtim5t5wdkr6f4g@vkgf2fogjirl



I think the reasonable next steps are:

- Commit "localbuf: *" commits


- Commit temp table tests, likely after lowering the minimum temp_buffers setting


- Pursue a fix of the smgr interupt issue on the referenced thread

  This can happen in parallel with AIO patches up to
  "aio: Implement support for reads in smgr/md/fd"


- Commit the core AIO infrastructure patch after doing a few more passes


- Commit IO worker support


- In parallel: Find a way to deal with the set_max_safe_fds() issue that we've
  been discussing on this thread recently. As that only affects io_uring, it
  doesn't have to block other patches going in.


- Do a round of review of the read_stream changes Thomas recently posted (and
  that are also included here)


- Try to get some more review for the bufmgr.c related changes. I've whacked
  them around a fair bit lately.


- Try to get Thomas to review my read_stream.c changes



Open items:

- The upstream BAS_BULKREAD is so small that throughput is substantially worse
  once a table reaches 1/4 shared_buffers. That patch in the patchset as-is is
  probably not good enough, although I am not sure about that


- The set_max_safe_fds() issue for io_uring


- Right now effective_io_concurrency cannot be set > 0 on Windows and other
  platforms that lack posix_fadvise. But with AIO we can read ahead without
  posix_fadvise().

  It'd not really make anything worse than today to not remove the limit, but
  it'd be pretty weird to prevent windows etc from benefiting from AIO.  Need
  to look around and see whether it would require anything other than doc
  changes.


Greetings,

Andres Freund