Horton

Re: AIO v2.5

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Noah Misch <noah@leadboat.com>
Cc: 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: 2025-03-29T14:48:10Z
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 aio: Fix reference to outdated name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

Hi,

On 2025-03-29 06:41:43 -0700, Noah Misch wrote:
> On Fri, Mar 28, 2025 at 11:35:23PM -0400, Andres Freund wrote:
> > But I finally got to a point where the code ends up readable, without undue
> > duplication.  It would, leaving some nasty hack aside, require a
> > errhint_internal() - but I can't imagine a reason against introducing that,
> > given we have it for the errmsg and errhint.
>
> Introducing that is fine.

Cool.


> > Here's the relevant code:
> >
> > 	/*
> > 	 * Treat a read that had both zeroed buffers *and* ignored checksums as a
> > 	 * special case, it's too irregular to be emitted the same way as the other
> > 	 * cases.
> > 	 */
> > 	if (zeroed_any && ignored_any)
> > 	{
> > 		Assert(zeroed_any && ignored_any);
> > 		Assert(nblocks > 1);	/* same block can't be both zeroed and ignored */
> > 		Assert(result.status != PGAIO_RS_ERROR);
> > 		affected_count = zeroed_or_error_count;
> >
> > 		ereport(elevel,
> > 				errcode(ERRCODE_DATA_CORRUPTED),
> > 				errmsg("zeroing %u pages and ignoring %u checksum failures among blocks %u..%u of relation %s",
> > 					   affected_count, checkfail_count, first, last, rpath.str),
>
> Translation stumbles on this one, because each of the first two %u are
> plural-sensitive.

Fair. We don't generally seem to have been very careful around this in relate
code, but there's no reason to just continue down that road when it's easy.

E.g. in md.c we unconditionally output "could not read blocks %u..%u in file \"%s\": %m"
even if it's just a single block...


> I'd do one of:
>
> - Call ereport() twice, once for zeroed pages and once for ignored checksums.
>   Since elevel <= ERROR here, that doesn't lose the second call.
>
> - s/pages/page(s)/ like msgid "There are %d other session(s) and %d prepared
>   transaction(s) using the database."

I think I like this better.


> > 	/*
> > 	 * The other messages are highly repetitive. To avoid duplicating a long
> > 	 * and complicated ereport(), gather the translated format strings
> > 	 * separately and then do one common ereport.
> > 	 */
> > 	if (result.status == PGAIO_RS_ERROR)
> > 	{
> > 		Assert(!zeroed_any);	/* can't have invalid pages when zeroing them */
> > 		affected_count = zeroed_or_error_count;
> > 		msg_one = _("invalid page in block %u of relation %s");
> > 		msg_mult = _("%u invalid pages among blocks %u..%u of relation %s");
> > 		det_mult = _("Block %u held first invalid page.");
> > 		hint_mult = _("See server log for the other %u invalid blocks.");
>
> For each hint_mult, we would usually use ngettext() instead of _().  (Would be
> errhint_plural() if not separated from its ereport().)  Alternatively,
> s/blocks/block(s)/ is fine.

I will go with the (s) here as well, this stuff is too rare to be worth having
pluralized messages imo.


> > Does that approach make sense?
>
> Yes.
> ...
> > I like the replacement.  It moves the important part to the front, and it's
> shorter.

Cool, I squashed them with the relevant changes now.


Attached is v2.14:

Changes:

- Added a commit to fix stats attribution of checksum errors, previously the
  checksum errors detected bufmgr.c/storage.c were always attributed to the
  current database

  This would have caused bigger issues with worker based IO, as IO workers
  aren't connected to databases.


- Added a commit to allow checksum error reports to happen in critical
  sections. For that a pgstat_prepare_report_checksum_failure() has to be
  called in the same backend, to report the critical section.

  Other suggestions for the name welcome.


- Expanded on the idea in 13 to track the number of invalid buffers in the
  IO's result, by also tracking checksum errors. Combined with the previous
  point, this fixes the issue of an assert during checksum failure reporting
  outlined in:

  https://postgr.es/m/5tyic6epvdlmd6eddgelv47syg2b5cpwffjam54axp25xyq2ga%40ptwkinxqo3az

  This required being a bit more careful with space in the error, to be able
  to squeeze in the checksum number.


- The ignore_checksum_failure of the issuer needs to be used when completing
  IO, not the one of the completor, particularly when using io_method=worker

  For that the access to ignore_checksum_failure had to be moved from
  PageIsVerified() to its callers.

  I added tests for ignore_checksum_failure, including its interplay with
  zero_damaged_pages.


- Deduplicated the error reporting in buffer_readv_report() somewhat by only
  having the selection of format strings be done in branches. I think this
  ends up a lot more readable than the huge ereport before.


- Added details about the changed error/warning logging to "bufmgr: Implement
  AIO read support"'s commit message.


- polished the commit to add PGAIO_RS_WARNING a bit, adding defines for the
  bit-widths of PgAioResult portions and added static asserts to verify them


- Squashed the changes that I had kept separately in v2.13, it was too hard to
  do that while doing the above changes.

  I did make the encoding function cast the arguments to uint32 before
  shifting. I think that's implied by the C integer promotion rules, but it
  seemed fishy enough to not want to believe in that.

  I also added a StaticAssertStmt() to ensure we are only using the available
  bit space.


- Added a test for a) checksum errors being detected b) CREATE DATABASE
  ... STRATEGY WAL_LOG

  The latter is interesting because it also provides test coverage for doing
  IO for objects in other databases.


- Removed an obsoleted inclusion of pg_trace.h in localbuf.c


TODO:

- I think the tests around zero_damaged_pages, ignore_checksum_failure should
  be expanded a bit more. There's two FIXME in the tests about that.

  At the moment there are two different test functions for zero_damaged_pages
  and ignore_checksum_failure, I'm not sure how good that is.

  I wanted to get this version out, because I have to run some errands,
  otherwise I'd have implemente them first...


Next steps:

- push the checksums stats fix


- unless somebody sees a reason to not use LOG_SERVER_ONLY in
  "aio: Implement support for reads in smgr/md/fd", push that

  Besides that the only change since Noah's last review of that commit is an
  added comment.


- push acronym, glossary change


- push pg_aios view (depends a tiny bit on the smgr/md/fd change above)


- push "localbuf: Track pincount in BufferDesc as well" - I think I addressed
  all of Noah's review feedback


- address the above TODO



Greetings,

Andres Freund