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: 2025-03-25T15:57:58Z
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 aio: Fix reference to outdated name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 2025-03-25 07:11:20 -0700, Noah Misch wrote:
> On Mon, Mar 24, 2025 at 10:52:19PM -0400, Andres Freund wrote:
> > Is it actually sane to use WARNING here? At least for ZERO_ON_ERROR that could
> > trigger a rather massive flood of messages to the client in a *normal*
> > situation. I'm thinking of something like an insert extending a relation some
> > time after an immediate restart and encountering a lot of FSM corruption (due
> > to its non-crash-safe-ness) during the search for free space and the
> > subsequent FSM vacuum.  It might be ok to LOG that, but sending a lot of
> > WARNINGs to the client seems not quite right.
> 
> Orthogonal to AIO, I do think LOG (or even DEBUG1?) is better for
> ZERO_ON_ERROR.  The ZERO_ON_ERROR case also should not use
> ERRCODE_DATA_CORRUPTED.  (That errcode shouldn't appear for business as usual.
> It should signify wrong or irretrievable query results, essentially.)

I strongly agree on the errcode - basically makes it much harder to use the
errcode to trigger alerting. And we don't have any other way to do that...

I'm, obviously, positive on not using WARNING for ZERO_ON_ERROR. I'm neutral
on LOG vs DEBUG1, I can see arguments for either.


> For zero_damaged_pages, WARNING seems at least defensible, and
> ERRCODE_DATA_CORRUPTED is right.  It wouldn't be the worst thing to change
> zero_damaged_pages to LOG and let the complete_shared runner log it, as long
> as we release-note that.  It's superuser-only, and the superuser can learn to
> check the log.  One typically should use zero_damaged_pages in one session at
> a time, so the logs won't be too confusing.

It's obviously tempting to go for that, I'm somewhat undecided what the best
way is right now.  There might be a compromise, see below:


> > If we want to implement it, I think we could introduce PGAIO_RS_WARN, which
> > then could tell the stager to issue the WARNING. It would add a bit of
> > distributed cost, both to callbacks and users of AIO, but it might not be too
> > bad.

FWIW, I prototyped this, it's not hard.

But it can't replace the current WARNING with 100% fidelity: If we read 60
blocks in a single smgrreadv, we today would would emit 60 WARNINGs.  But we
can't encode that many block offset in single PgAioResult, there's not enough
space, and enlarging it far enough doesn't seem to make sense either.


What we *could* do is to emit one WARNING for each bufmgr.c smgrstartreadv(),
with that warning saying that there were N zeroed blocks in a read from block
N to block Y and a HINT saying that there are more details in the server log.



> Another thought on complete_shared running on other backends: I wonder if we
> should push an ErrorContextCallback that adds "CONTEXT: completing I/O of
> other process" or similar, so people wonder less about how "SELECT FROM a" led
> to a log message about IO on table "b".

I've been wondering about that as well, and yes, we probably should.

I'd add the pid of the backend that started the IO to the message - although
need to check whether we're trying to keep PIDs of other processes from
unprivileged users.

I think we probably should add a similar, but not equivalent, context in io
workers. Maybe "I/O worker executing I/O on behalf of process %d".

Greetings,

Andres Freund