Horton

Re: AIO v2.5

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Alexander Lakhin <exclusion@gmail.com>
Cc: Noah Misch <noah@leadboat.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: 2025-04-14T16:06:24Z
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 aio: Fix reference to outdated name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

Hi,

On 2025-04-13 09:00:01 +0300, Alexander Lakhin wrote:
> 07.04.2025 22:10, Alexander Lakhin wrote:
> > > I ran it for a while in a VM, it hasn't triggered yet. Neither on xfs nor on
> > > tmpfs.
> > 
> > Before sharing the script I tested it on two my machines, but I had
> > anticipated that the error can be hard to reproduce. Will try to reduce
> > the reproducer...
> 
> I've managed to reduce it to the following:

Thanks a lot for working on that!


> [reproducer]
> 
> It fails for me as below:
> iteration 13 (jobs: 25)
> Sun Apr 13 05:31:47 AM UTC 2025
> iteration 14 (jobs: 67)
> Sun Apr 13 05:31:50 AM UTC 2025
> dropdb: error: database removal failed: ERROR:  could not read blocks 0..0 in file "global/1213": Operation canceled
> 2025-04-13 05:31:58.930 UTC [1153451] LOG:  could not read blocks 0..0 in file "global/1213": Operation canceled
> 2025-04-13 05:31:58.930 UTC [1153451] CONTEXT:  completing I/O on behalf of process 1153456
> 2025-04-13 05:31:58.930 UTC [1153451] STATEMENT:  DROP DATABASE db5;
> 2025-04-13 05:31:58.930 UTC [1153456] ERROR:  could not read blocks 0..0 in file "global/1213": Operation canceled
> 2025-04-13 05:31:58.930 UTC [1153456] STATEMENT:  DROP DATABASE db6;
> 2025-04-13 05:31:58.931 UTC [1034758] LOG:  checkpoint complete: wrote 3
> buffers (0.0%), wrote 0 SLRU buffers; 0 WAL file(s) added, 0 removed, 0
> recycled; write=0.002 s, sync=0.001 s, total=0.002 s; sync files=0,
> longest=0.000 s, average=0.000 s; distance=18 kB, estimate=458931 kB;
> lsn=16/54589E08, redo lsn=16/54586F88
> 2025-04-13 05:31:58.931 UTC [1034758] LOG:  checkpoint starting: immediate force wait

Unfortunately I'm several hundred iterations in, without reproducing the
issue. I'm bad at statistics, but I think that makes it rather unlikely that I
will, without changing some aspect.

Was this an assert enabled build? What compiler and what optimization settings
did you use? Do you have huge pages configured (so that the default
huge_pages=try would end up with huge pages)?

So far I've been trying to use a cassert enabled build built with -O0, without
huge pages. After the current test run I'll switch to cassert+-O2.



> I reproduced this error on three different machines (all are running
> Ubuntu 24.04, two with kernel version 6.8, one with 6.11), with PGDATA
> located on tmpfs.

That's another variable to try - so far I've been trying this on 6.15.0-rc1
[1].  I guess I'll have to set up a ubuntu 24.04 VM and try with that.

Greetings,

Andres Freund


[1] I wanted to play with io_uring changes that were recently merged. Namely
support for readv/writev of "fixed" buffers. That avoids needing to pin/unpin
buffers while IO is ongoing, which turns out to be a noticeable bottleneck in
some workloads, particularly when using 1GB huge pages.