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: 2025-03-25T02:20:37Z
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 aio: Fix reference to outdated name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 Thu, Mar 20, 2025 at 09:58:37PM -0400, Andres Freund wrote:
> Subject: [PATCH v2.11 09/27] bufmgr: Implement AIO read support

[I checked that v2.12 doesn't invalidate these review comments, but I didn't
technically rebase the review onto v2.12's line numbers.]

>  static void
>  TerminateBufferIO(BufferDesc *buf, bool clear_dirty, uint32 set_flag_bits,
> -				  bool forget_owner)
> +				  bool forget_owner, bool syncio)
>  {
>  	uint32		buf_state;
>  
> @@ -5586,6 +5636,14 @@ TerminateBufferIO(BufferDesc *buf, bool clear_dirty, uint32 set_flag_bits,
>  	if (clear_dirty && !(buf_state & BM_JUST_DIRTIED))
>  		buf_state &= ~(BM_DIRTY | BM_CHECKPOINT_NEEDED);
>  
> +	if (!syncio)
> +	{
> +		/* release ownership by the AIO subsystem */
> +		Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
> +		buf_state -= BUF_REFCOUNT_ONE;
> +		pgaio_wref_clear(&buf->io_wref);
> +	}

Looking at the callers:

ZeroAndLockBuffer[1083]        TerminateBufferIO(bufHdr, false, BM_VALID, true, true);
ExtendBufferedRelShared[2869]  TerminateBufferIO(buf_hdr, false, BM_VALID, true, true);
FlushBuffer[4827]              TerminateBufferIO(buf, true, 0, true, true);
AbortBufferIO[6637]            TerminateBufferIO(buf_hdr, false, BM_IO_ERROR, false, true);
buffer_readv_complete_one[7279] TerminateBufferIO(buf_hdr, false, set_flag_bits, false, false);
buffer_writev_complete_one[7427] TerminateBufferIO(buf_hdr, clear_dirty, set_flag_bits, false, false);

I think we can improve on the "syncio" arg name.  The first two aren't doing
IO, and AbortBufferIO() may be cleaning up what would have been an AIO if it
hadn't failed early.  Perhaps name the arg "release_aio" and pass
release_aio=true instead of syncio=false (release_aio = !syncio).

> +		 * about which buffers are target by IO can be hard to debug, making

s/target/targeted/

> +static pg_attribute_always_inline PgAioResult
> +buffer_readv_complete_one(uint8 buf_off, Buffer buffer, uint8 flags,
> +						  bool failed, bool is_temp)
> +{
...
> +		if ((flags & READ_BUFFERS_ZERO_ON_ERROR) || zero_damaged_pages)
> +		{
> +			ereport(WARNING,
> +					(errcode(ERRCODE_DATA_CORRUPTED),
> +					 errmsg("invalid page in block %u of relation %s; zeroing out page",

My earlier review requested s/LOG/WARNING/, but I wasn't thinking about this
in full depth.  In the !is_temp case, this runs in a complete_shared callback.
A process unrelated to the original IO may run this callback.  That's
unfortunate in two ways.  First, that other process's client gets an
unexpected WARNING.  The process getting the WARNING may not even have
zero_damaged_pages enabled.  Second, the client of the process that staged the
IO gets no message.

AIO ERROR-level messages handle this optimally.  We emit a LOG-level message
in the process that runs the complete_shared callback, and we arrange for the
ERROR-level message in the stager.  That would be ideal here: LOG in the
complete_shared runner, WARNING in the stager.

One could simplify things by forcing io_method=sync under ZERO_ON_ERROR ||
zero_damaged_pages, perhaps as a short-term approach.

Thoughts?