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: 2025-03-20T18:19:04Z
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 aio: Fix reference to outdated name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 01:05:05PM -0400, Andres Freund wrote:
> On 2025-03-19 18:17:37 -0400, Andres Freund wrote:
> > On 2025-03-19 14:25:30 -0700, Noah Misch wrote:
> > > > +		 * marked as failed. In case of a partial read, some buffers may be
> > > > +		 * ok.
> > > > +		 */
> > > > +		failed =
> > > > +			prior_result.status == ARS_ERROR
> > > > +			|| prior_result.result <= buf_off;
> > >
> > > I didn't run an experiment to check the following, but I think this should be
> > > s/<=/</.  Suppose we requested two blocks and read some amount of bytes
> > > [1*BLCKSZ, 2*BLSCKSZ - 1].  md_readv_complete will store result=1.  buf_off==0
> > > should compute failed=false here, but buf_off==1 should compute failed=true.
> > 
> > Huh, you might be right. I thought I wrote a test for this, I wonder why it
> > didn't catch the problem...
> 
> It was correct as-is. With result=1 you get precisely the result you describe
> as the desired outcome, no?
>    prior_result.result <= buf_off
>    ->
>    1 <= 0 -> failed = 0
>    1 <= 1 -> failed = 1
> 
> but if it were < as you suggest:
> 
>    prior_result.result < buf_off
>    ->
>    1 < 0 -> failed = 0
>    1 < 1 -> failed = 0
> 
> I.e. we would assume that the second buffer also completed.

That's right.  I see it now.  My mistake.

> What does concern me is that the existing tests do *not* catch the problem if
> I turn "<=" into "<".  The second buffer in this case wrongly gets marked as
> valid. We do retry the read (because bufmgr.c thinks only one block was read),
> but find the buffer to already be valid.
> 
> The reason the test doesn't fail, is that the way I set up the "short read"
> tests. The injection point runs after the IO completed and just modifies the
> result. However, the actual buffer contents still got modified.
> 
> 
> The easiest way around that seems to be to have the injection point actually
> zero out the remaining memory.

Sounds reasonable and sufficient.

FYI, I've resumed the comprehensive review.  That's still ongoing.