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: 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: 2025-04-01T16:07:27Z
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 aio: Fix reference to outdated name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 Tue, Apr 01, 2025 at 11:55:20AM -0400, Andres Freund wrote:
> On 2025-04-01 08:11:59 -0700, Noah Misch wrote:
> > On Mon, Mar 31, 2025 at 08:41:39PM -0400, Andres Freund wrote:

> I haven't yet pushed the changes, but will work on that in the afternoon.
> 
> I plan to afterwards close the CF entry and will eventually create a new one
> for write support, although probably only rebasing onto
> https://postgr.es/m/stj36ea6yyhoxtqkhpieia2z4krnam7qyetc57rfezgk4zgapf%40gcnactj4z56m
> and addressing some of the locking issues.

Sounds good.

> WRT the locking issues, I've been wondering whether we could make
> LWLockWaitForVar() work that purpose, but I doubt it's the right approach.
> Probably better to get rid of the LWLock*Var functions and go for the approach
> I had in v1, namely a version of LWLockAcquire() with a callback that gets
> called between LWLockQueueSelf() and PGSemaphoreLock(), which can cause the
> lock acquisition to abort.

What are the best thing(s) to read to understand the locking issues?

> > > +# Verify checksum handling when creating database from an invalid database.
> > > +# This also serves as a minimal check that cross-database IO is handled
> > > +# reasonably.
> >
> > To me, "invalid database" is a term of art from the message "cannot connect to
> > invalid database".  Hence, I would change "invalid database" to "database w/
> > invalid block" or similar, here and below.  (Alternatively, just delete "from
> > an invalid database".  It's clear from the context.)
> 
> Yea, I agree, this is easy to misunderstand when stepping back. I went for "with
> an invalid block".

Sounds good.

> > > +	if (corrupt_checksum)
> > > +	{
> > > +		bool		successfully_corrupted = 0;
> > > +
> > > +		/*
> > > +		 * Any single modification of the checksum could just end up being
> > > +		 * valid again. To be sure
> > > +		 */
> >
> > Unfinished sentence.
> 
> Oops. See below.
> 
> 
> > That said, I'm not following why we'd need this loop.  If this test code
> > were changing the input to the checksum, it's true that an input bit flip
> > might reach the same pd_checksum.  The test case is changing pd_checksum,
> > not the input bits.
> 
> We might be changing the input, due to the zero/corrupt_header options. Or we
> might be called on a page that is *already* corrupted. I did encounter that
> situation once while writing tests, where the tests only passed if I made the
> + 1 a + 2. Which was, uh, rather confusing and left me feel like I was cursed
> that day.

Got it.

> > I don't see how changing pd_checksum could leave the
> > page still valid.  There's only one valid pd_checksum value for a given
> > input page.
> 
> I updated the comment to:
> 		/*
> 		 * Any single modification of the checksum could just end up being
> 		 * valid again, due to e.g. corrupt_header changing the data in a way
> 		 * that'd result in the "corrupted" checksum, or the checksum already
> 		 * being invalid. Retry in that, unlikely, case.
> 		 */

Works for me.