Horton

Re: AIO v2.5

Noah Misch <noah@leadboat.com>

View thread
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: 2025-03-20T01:11:18Z
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 aio: Fix reference to outdated name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 Wed, Mar 19, 2025 at 06:17:37PM -0400, Andres Freund wrote:
> On 2025-03-19 14:25:30 -0700, Noah Misch wrote:
> > commit 55b454d wrote:
> > >     aio: Infrastructure for io_method=worker
> >
> > > +		/* Try to launch one. */
> > > +		child = StartChildProcess(B_IO_WORKER);
> > > +		if (child != NULL)
> > > +		{
> > > +			io_worker_children[id] = child;
> > > +			++io_worker_count;
> > > +		}
> > > +		else
> > > +			break;				/* XXX try again soon? */
> >
> > I'd change the comment to something like one of:
> >
> >   retry after DetermineSleepTime()
> >   next LaunchMissingBackgroundProcesses() will retry in <60s
> 
> Hm, we retry more frequently that that if there are new connections...  Maybe
> just "try again next time"?

Works for me.

> > On Tue, Mar 18, 2025 at 04:12:18PM -0400, Andres Freund wrote:
> > > Subject: [PATCH v2.10 08/28] bufmgr: Implement AIO read support
> >
> > Some comments about BM_IO_IN_PROGRESS may need updates.  This paragraph:
> >
> > * The BM_IO_IN_PROGRESS flag acts as a kind of lock, used to wait for I/O on a
> > buffer to complete (and in releases before 14, it was accompanied by a
> > per-buffer LWLock).  The process doing a read or write sets the flag for the
> > duration, and processes that need to wait for it to be cleared sleep on a
> > condition variable.
> 
> First draft:
> * The BM_IO_IN_PROGRESS flag acts as a kind of lock, used to wait for I/O on a
> buffer to complete (and in releases before 14, it was accompanied by a
> per-buffer LWLock).  The process start a read or write sets the flag. When the
s/start/starting/
> I/O is completed, be it by the process that initiated the I/O or by another
> process, the flag is removed and the Buffer's condition variable is signalled.
> Processes that need to wait for the I/O to complete can wait for asynchronous
> I/O to using BufferDesc->io_wref and for BM_IO_IN_PROGRESS to be unset by
s/to using/by using/
> sleeping on the buffer's condition variable.

Sounds good.

> > And these individual lines from "git grep BM_IO_IN_PROGRESS":
> >
> >  *	i.e at most one BM_IO_IN_PROGRESS bit is set per proc.
> >
> > The last especially.
> 
> Huh - yea.  This isn't a "new" issue, I think I missed this comment in 16's
> 12f3867f5534.  I think the comment can just be deleted?

Hmm, yes, it's orthogonal to $SUBJECT and deletion works fine.

> > 		 * I/O already in progress.  We already hold BM_IO_IN_PROGRESS for the
> > 	 * only one process at a time can set the BM_IO_IN_PROGRESS bit.
> > 	 * only one process at a time can set the BM_IO_IN_PROGRESS bit.
> 
> > For the other three lines and the paragraph, the notion
> > of a process "holding" BM_IO_IN_PROGRESS or being the process to "set" it or
> > being the process "doing a read" becomes less significant when one process
> > starts the IO and another completes it.
> 
> Hm. I think they'd be ok as-is, but we can probably improve them. Maybe

Looking again, I agree they're okay.

> 
> 	 * Now it's safe to write buffer to disk. Note that no one else should
> 	 * have been able to write it while we were busy with log flushing because
> 	 * we got the exclusive right to perform I/O by setting the
> 	 * BM_IO_IN_PROGRESS bit.

That's fine too.  Maybe s/perform/stage/ or s/perform/start/.

> > I see this relies on md_readv_complete having converted "result" to blocks.
> > Was there some win from doing that as opposed to doing the division here?
> > Division here ("blocks_read = prior_result.result / BLCKSZ") would feel easier
> > to follow, to me.
> 
> It seemed like that would be wrong layering - what if we had an smgr that
> could store data in a compressed format? The raw read would be of a smaller
> size. The smgr API deals in BlockNumbers, only the md.c layer should know
> about bytes.

I hadn't thought of that.  That's a good reason.