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: 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: 2025-03-20T17:05:05Z
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 aio: Fix reference to outdated name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 2025-03-19 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.


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. Not pretty, but it'd be harder to just submit
shortend IOs in multiple IO methods.  It'd be even better if we could
trivially use something like randomize_mem(), but it's only conditionally
compiled...

Greetings,

Andres Freund