Horton

Re: AIO v2.5

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Andres Freund <andres@anarazel.de>
Cc: Antonin Houska <ah@cybertec.at>, 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>
Date: 2025-03-26T00:19:15Z
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 aio: Fix reference to outdated name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 Mon, Mar 24, 2025 at 09:18:06PM -0400, Andres Freund wrote:
> Attached v2.12, with the following changes:

> TODO:

>   Wonder if it's worth adding some coverage for when checksums are disabled?
>   Probably not necessary?

Probably not necessary, agreed.  Orthogonal to AIO, it's likely worth a CI
"SPECIAL" and/or buildfarm animal that runs all tests w/ checksums disabled.


> Subject: [PATCH v2.12 01/28] aio: Be more paranoid about interrupts

Ready for commit


> Subject: [PATCH v2.12 02/28] aio: Pass result of local callbacks to
>  ->report_return

Ready for commit w/ up to one cosmetic change:

> @@ -296,7 +299,9 @@ pgaio_io_call_complete_local(PgAioHandle *ioh)
>  
>  	/*
>  	 * Note that we don't save the result in ioh->distilled_result, the local
> -	 * callback's result should not ever matter to other waiters.
> +	 * callback's result should not ever matter to other waiters. However, the
> +	 * local backend does care, so we return the result as modified by local
> +	 * callbacks, which then can be passed to ioh->report_return->result.
>  	 */
>  	pgaio_debug_io(DEBUG3, ioh,
>  				   "after local completion: distilled result: (status %s, id %u, error_data %d, result %d), raw_result: %d",

Should this debug message remove the word "distilled", since this commit
solidifies distilled_result as referring to the complete_shared result?


> Subject: [PATCH v2.12 03/28] aio: Add liburing dependency

Ready for commit


> Subject: [PATCH v2.12 04/28] aio: Add io_method=io_uring

Ready for commit w/ open_fd.fixup


> Subject: [PATCH v2.12 05/28] aio: Implement support for reads in smgr/md/fd

Ready for commit w/ up to two cosmetic changes:

> +/*
> + * AIO error reporting callback for mdstartreadv().
> + *
> + * Errors are encoded as follows:
> + * - PgAioResult.error_data != 0 encodes IO that failed with errno != 0

I recommend replacing "errno != 0" with either "that errno" or "errno ==
error_data".

Second, the aio_internal.h comment changes discussed in
postgr.es/m/20250325155808.f7.nmisch@google.com and earlier.


> Subject: [PATCH v2.12 06/28] aio: Add README.md explaining higher level design

Ready for commit

(This and the previous patch have three spots that would change with the
s/prep/start/ renames.  No opinion on whether to rename before or rename
after.)


> Subject: [PATCH v2.12 07/28] localbuf: Track pincount in BufferDesc as well

The plan here looks good:
postgr.es/m/dbeeaize47y7esifdrinpa2l7cqqb67k72exvuf3appyxywjnc@7bt76mozhcy2


> Subject: [PATCH v2.12 08/28] bufmgr: Implement AIO read support

See review here and later discussion:
postgr.es/m/20250325022037.91.nmisch@google.com


> Subject: [PATCH v2.12 09/28] bufmgr: Use AIO in StartReadBuffers()

Ready for commit after a batch of small things, all but one of which have no
implications beyond code cosmetics.  This is my first comprehensive review of
this patch.  I like the test coverage (by the end of the patch series).  For
anyone else following, I found "diff -w" helpful for the bufmgr.c changes.
That's because a key part is former WaitReadBuffers() code moving up an
indentation level to its home in new subroutine AsyncReadBuffers().

>  	Assert(*nblocks == 1 || allow_forwarding);
>  	Assert(*nblocks > 0);
>  	Assert(*nblocks <= MAX_IO_COMBINE_LIMIT);
> +	Assert(*nblocks == 1 || allow_forwarding);

Duplicates the assert three lines back.

> +		nblocks = aio_ret->result.result;
> +
> +		elog(DEBUG3, "partial read, will retry");
> +
> +	}
> +	else if (aio_ret->result.status == PGAIO_RS_ERROR)
> +	{
> +		pgaio_result_report(aio_ret->result, &aio_ret->target_data, ERROR);
> +		nblocks = 0;			/* silence compiler */
> +	}
>  
>  	Assert(nblocks > 0);
>  	Assert(nblocks <= MAX_IO_COMBINE_LIMIT);
>  
> +	operation->nblocks_done += nblocks;

I struggled somewhat from the variety of "nblocks" variables: this local
nblocks, operation->nblocks, actual_nblocks, and *nblocks in/out parameters of
some functions.  No one of them is clearly wrong to use the name, and some of
these names are preexisting.  That said, if you see opportunities to push in
the direction of more-specific names, I'd welcome it.

For example, this local variable could become add_to_nblocks_done instead.

> +		AsyncReadBuffers(operation, &nblocks);

I suggest renaming s/nblocks/ignored_nblocks_progress/ here.

> +	 * If we need to wait for IO before we can get a handle, submit already
> +	 * staged IO first, so that other backends don't need to wait. There

s/already staged/already-staged/.  Normally I'd skip this as nitpicking, but I
misread this particular sentence twice, as "submit" being the subject that
"staged" something.  (It's still nitpicking, alas.)

>  		/*
>  		 * How many neighboring-on-disk blocks can we scatter-read into other
>  		 * buffers at the same time?  In this case we don't wait if we see an
> -		 * I/O already in progress.  We already hold BM_IO_IN_PROGRESS for the
> +		 * I/O already in progress.  We already set BM_IO_IN_PROGRESS for the
>  		 * head block, so we should get on with that I/O as soon as possible.
> -		 * We'll come back to this block again, above.
> +		 *
> +		 * We'll come back to this block in the next call to
> +		 * StartReadBuffers() -> AsyncReadBuffers().

Did this mean to say "WaitReadBuffers() -> AsyncReadBuffers()"?  I'm guessing
so, since WaitReadBuffers() is the one that loops.  It might be referring to
read_stream_start_pending_read()'s next StartReadBuffers(), though.

I think this could just delete the last sentence.  The function header comment
already mentions the possibility of reading a subset of the request.  This
spot doesn't need to detail how the higher layers come back to here.

> +		smgrstartreadv(ioh, operation->smgr, forknum,
> +					   blocknum + nblocks_done,
> +					   io_pages, io_buffers_len);
> +		pgstat_count_io_op_time(io_object, io_context, IOOP_READ,
> +								io_start, 1, *nblocks_progress * BLCKSZ);

We don't assign *nblocks_progress until lower in the function, so I think
"io_buffers_len" should replace "*nblocks_progress" here.  (This is my only
non-cosmetic comment on this patch.)


> Subject: [PATCH v2.12 10/28] aio: Basic read_stream adjustments for real AIO

(Still reviewing this and later patches, but incidental observations follow.)


> Subject: [PATCH v2.12 16/28] aio: Add test_aio module

> +use List::Util qw(sample);

sample() is new in 2020:
https://metacpan.org/release/PEVANS/Scalar-List-Utils-1.68/source/Changes#L100

Hence, I'd expect some buildfarm failures.  I'd try to use shuffle(), then
take the first N elements.

> +++ b/src/test/modules/test_aio/test_aio.c
> @@ -0,0 +1,712 @@
> +/*-------------------------------------------------------------------------
> + *
> + * delay_execution.c
> + *		Test module to allow delay between parsing and execution of a query.
> + *
> + * The delay is implemented by taking and immediately releasing a specified
> + * advisory lock.  If another process has previously taken that lock, the
> + * current process will be blocked until the lock is released; otherwise,
> + * there's no effect.  This allows an isolationtester script to reliably
> + * test behaviors where some specified action happens in another backend
> + * between parsing and execution of any desired query.
> + *
> + * Copyright (c) 2020-2025, PostgreSQL Global Development Group
> + *
> + * IDENTIFICATION
> + *	  src/test/modules/test_aio/test_aio.c

To elaborate on my last review, the entire header comment was a copy from
delay_execution.c.  v2.12 fixes the IDENTIFICATION, but the rest needs
updates.

Thanks,
nm