Horton

Re: AIO v2.0

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Jakub Wartak <jakub.wartak@enterprisedb.com>, Thomas Munro <thomas.munro@gmail.com>
Cc: pgsql-hackers@postgresql.org, Heikki Linnakangas <hlinnaka@iki.fi>, 陈宗志 <baotiao@gmail.com>
Date: 2025-01-06T16:28:39Z
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 aio: Fix reference to outdated name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 2024-12-19 17:29:12 -0500, Andres Freund wrote:
> > Not about patch itself, but questions about related stack functionality:
> > ----------------------------------------------------------------------------------------------------
> >
> >
> > 7. Is pg_stat_aios still on the table or not ? (AIO 2021 had it). Any hints
> > on how to inspect real I/O calls requested to review if the code is issuing
> > sensible calls: there's no strace for uring, or do you stick to DEBUG3 or
> > perhaps using some bpftrace / xfsslower is the best way to go ?
> 
> I think we still want something like it, but I don't think it needs to be in
> the initial commits.

After I got this question from Thomas as well, I started hacking one up.

What information would you like to see?

Here's what I currently have:
┌─[ RECORD 1 ]───┬────────────────────────────────────────────────┐
│ pid            │ 358212                                         │
│ io_id          │ 2050                                           │
│ io_generation  │ 4209                                           │
│ state          │ COMPLETED_SHARED                               │
│ operation      │ read                                           │
│ offset         │ 509083648                                      │
│ length         │ 262144                                         │
│ subject        │ smgr                                           │
│ iovec_data_len │ 32                                             │
│ raw_result     │ 262144                                         │
│ result         │ OK                                             │
│ error_desc     │ (null)                                         │
│ subject_desc   │ blocks 1372864..1372895 in file "base/5/16388" │
│ flag_sync      │ f                                              │
│ flag_localmem  │ f                                              │
│ flag_buffered  │ t                                              │
├─[ RECORD 2 ]───┼────────────────────────────────────────────────┤
│ pid            │ 358212                                         │
│ io_id          │ 2051                                           │
│ io_generation  │ 4199                                           │
│ state          │ IN_FLIGHT                                      │
│ operation      │ read                                           │
│ offset         │ 511967232                                      │
│ length         │ 262144                                         │
│ subject        │ smgr                                           │
│ iovec_data_len │ 32                                             │
│ raw_result     │ (null)                                         │
│ result         │ UNKNOWN                                        │
│ error_desc     │ (null)                                         │
│ subject_desc   │ blocks 1373216..1373247 in file "base/5/16388" │
│ flag_sync      │ f                                              │
│ flag_localmem  │ f                                              │
│ flag_buffered  │ t                                              │


I didn't think that pg_stat_* was quite the right namespace, given that it
shows not stats, but the currently ongoing IOs.  I am going with pg_aios for
now, but I don't particularly like that.


I think we'll want a pg_stat_aio as well, tracking things like:

- how often the queue to IO workes was full
- how many times we submitted IO to the kernel (<= #ios with io_uring)
- how many times we asked the kernel for events (<= #ios with io_uring)
- how many times we had to wait for in-flight IOs before issuing more IOs

Greetings,

Andres Freund