Horton

Re: AIO v2.0

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org
Date: 2024-09-06T01:42:24Z
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 aio: Fix reference to outdated name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 Sun, 1 Sept 2024 at 18:28, Andres Freund <andres@anarazel.de> wrote:
>                                 0 workers       1 worker        2 workers       4 workers
> master:                         65.753          33.246          21.095          12.918
> aio v2.0, worker:               21.519          12.636          10.450          10.004
> aio v2.0, uring*:               31.446          17.745          12.889          10.395
> aio v2.0, uring**               23.497          13.824          10.881          10.589
> aio v2.0, direct, worker:       22.377          11.989          09.915          09.772
> aio v2.0, direct, uring*:       24.502          12.603          10.058          09.759

I took this for a test drive on an AMD 3990x machine with a 1TB
Samsung 980 Pro SSD on PCIe 4.  I only tried io_method = io_uring, but
I did try with and without direct IO.

This machine has 64GB RAM and I was using ClickBench Q2 [1], which is
"SELECT SUM(AdvEngineID), COUNT(*), AVG(ResolutionWidth) FROM hits;"
(for some reason they use 0-based query IDs). This table is 64GBs
without indexes.

I'm seeing direct IO slower than buffered IO with smaller worker
counts. That's counter to what I would have expected as I'd have
expected the memcpys from the kernel space to be quite an overhead in
the buffered IO case. With larger worker counts the bottleneck is
certainly disk. The part that surprised me was that the bottleneck is
reached more quickly with buffered IO. I was seeing iotop going up to
5.54GB/s at higher worker counts.

times in milliseconds
workers    buffered    direct    cmp
0    58880    102852    57%
1    33622    53538    63%
2    24573    40436    61%
4    18557    27359    68%
8    14844    17330    86%
16    12491    12754    98%
32    11802    11956    99%
64    11895    11941    100%

Is there some other information I can provide to help this make sense?
(Or maybe it does already to you.)

David

[1] https://github.com/ClickHouse/ClickBench/blob/main/postgresql-tuned/queries.sql