Horton

Re: AIO v2.5

Alexander Lakhin <exclusion@gmail.com>

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From: Alexander Lakhin <exclusion@gmail.com>
To: Andres Freund <andres@anarazel.de>
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: 2025-04-15T18:00:00Z
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 aio: Fix reference to outdated name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

Attachments

Hello Andres,

14.04.2025 19:06, Andres Freund wrote:
> 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)?

Yes, I used --enable-cassert; no explicit optimization setting and no huge
pages configured. pg_config says:
CONFIGURE =  '--enable-debug' '--enable-cassert' '--enable-tap-tests' '--with-liburing'
CC = gcc
CPPFLAGS = -D_GNU_SOURCE
CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels 
-Wmissing-format-attribute -Wimplicit-fallthrough=3 -Wcast-function-type -Wshadow=compatible-local -Wformat-security 
-fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -Wno-stringop-truncation -g -O2

Please look at the complete script attached. I've just run it and got:
iteration 56 (jobs: 44)
Tue Apr 15 06:30:52 PM CEST 2025
dropdb: error: database removal failed: ERROR:  could not read blocks 0..0 in file "global/1213": Operation canceled
2025-04-15 18:31:00.650 CEST [1612266] LOG:  could not read blocks 0..0 in file "global/1213": Operation canceled
2025-04-15 18:31:00.650 CEST [1612266] CONTEXT:  completing I/O on behalf of process 1612271
2025-04-15 18:31:00.650 CEST [1612266] STATEMENT:  DROP DATABASE db3;

I used gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0, but now I've also
reproduced the issue with CC=clang (18.1.3 (1ubuntu1)).

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

>> 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.

Best regards,
Alexander Lakhin
Neon (https://neon.tech)