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: 2025-04-25T16:44:14Z
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 aio: Fix reference to outdated name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 2025-04-15 21:00:00 +0300, Alexander Lakhin wrote:
> Please take a look also at the simple reproducer for the crash inside
> pg_get_aios() I mentioned upthread:
> for i in {1..100}; do
>   numjobs=12
>   echo "iteration $i"
>   date
>   for ((j=1;j<=numjobs;j++)); do
>     ( createdb db$j; for k in {1..300}; do
>         echo "CREATE TABLE t (a INT); CREATE INDEX ON t (a); VACUUM t;
>               SELECT COUNT(*) >= 0 AS ok FROM pg_aios; " \
>         | psql -d db$j >/dev/null 2>&1;
>       done; dropdb db$j; ) &
>   done
>   wait
>   psql -c 'SELECT 1' || break;
> done
> 
> it fails for me as follows:
> iteration 20
> Tue Apr 15 07:21:29 PM EEST 2025
> dropdb: error: connection to server on socket "/tmp/.s.PGSQL.55432" failed: No such file or directory
>        Is the server running locally and accepting connections on that socket?
> ...
> 2025-04-15 19:21:30.675 EEST [3111699] LOG:  client backend (PID 3320979) was terminated by signal 11: Segmentation fault
> 2025-04-15 19:21:30.675 EEST [3111699] DETAIL:  Failed process was running: SELECT COUNT(*) >= 0 AS ok FROM pg_aios;
> 2025-04-15 19:21:30.675 EEST [3111699] LOG:  terminating any other active server processes

Thanks for that.  The bug turns out to be pretty stupid - pgaio_io_reclaim()
resets the fields in PgAioHandle *before* updating the generation/state. That
opens up a window in which pg_get_aios() thinks the copied PgAioHandle is
valid, even though it was taken while the fields were being reset.

Once I had figured that out, it was easy to make it more reproducible - put a
pg_usleep() between the fields being reset in pgaio_io_reclaim() and the
generation increase / state update.

The fix is simple, increment generation and state before resetting fields.

Will push the fix for that soon.

Greetings,

Andres Freund