Horton

Re: AIO v2.5

Noah Misch <noah@leadboat.com>

View thread
From: Noah Misch <noah@leadboat.com>
To: Andres Freund <andres@anarazel.de>
Cc: Alexander Lakhin <exclusion@gmail.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>, Antonin Houska <ah@cybertec.at>
Date: 2025-05-09T02:22:27Z
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 aio: Fix reference to outdated name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, May 08, 2025 at 09:06:18PM -0400, Andres Freund wrote:
> On 2025-05-02 20:05:11 -0700, Noah Misch wrote:
> > On Wed, Apr 30, 2025 at 04:00:35PM -0400, Andres Freund wrote:

> We do need to hold interrupts in a few other places, I think - with some debug
> infrastructure (things like calling ProcessBarrierSmgrRelease() whenever
> interrupts could be processed and calling CFI() in errstart() in its return
> false case) it's possible to find state confusions which trigger
> assertions. The issue is that pgaio_io_update_state() contains a
> pgaio_debug_io() and executing pgaio_closing_fd() in places that call
> pgaio_io_update_state() doesn't end well.  There's a similar danger with the
> debug message in pgaio_io_reclaim().
> 
> In the attached patch I added an assertion to pgaio_io_update_state()
> verifying that interrupts are held and added code to hold interrupts in the
> relevant places.

Works for me.

> > For the "no free IOs despite no in-flight IOs" case, I'd replace the
> > ereport(ERROR) with "return;" since we now know interrupt processing reclaimed
> > an IO.
> 
> Hm - it seems better to me to check if there are now free handles and return
> if that's the case, but to keep the error check in case there actually is no
> free IO? That seems like a not implausible bug...

Works for me.

> > Then decide what protection if any, we need against bugs causing an
> > infinite loop in caller pgaio_io_acquire().  What's the case motivating the
> > unbounded loop in pgaio_io_acquire(), as opposed to capping at two
> > pgaio_io_acquire_nb() calls?  If the theory is that pgaio_io_acquire() could
> > be reentrant, what scenario would reach that reentrancy?
> 
> I do not remember why I wrote this as an endless loop.  If you prefer I could
> change that as part of this patch.

I asked because it would be sad to remove the ereport(ERROR) like I proposed
and then have a bug cause a real infinite loop.  Removing the loop was one way
to prove that can't happen.  As you say, another way would be keeping the
ereport(ERROR) and guarding it with a free-handles check, like in your patch
today.  I don't have a strong preference between those.

> It does seem rather dangerous that errstart() processes interrupts for debug
> messages, but only if the debug message is actually logged. That's really a
> recipe for hard to find bugs.  I wonder if we should, at least in assertion
> mode, process interrupts even if not emitting the message.

Yes, that sounds excellent to have.