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: 2025-03-30T02:45:13Z
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 aio: Fix reference to outdated name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 Sat, Mar 29, 2025 at 08:39:54PM -0400, Andres Freund wrote:
> On 2025-03-29 14:29:29 -0700, Noah Misch wrote:
> > On Wed, Mar 26, 2025 at 09:07:40PM -0400, Andres Freund wrote:

> > The choice between LOG and LOG_SERVER_ONLY doesn't matter much for $SUBJECT.
> > If a client has decided to set client_min_messages that high, the client might
> > be interested in the fact that it got side-tracked completing someone else's
> > IO.  On the other hand, almost none of those sidetrack events will produce
> > messages.  The main argument I'd envision for LOG_SERVER_ONLY is that we
> > consider the message content sensitive, but I don't see the message content as
> > materially sensitive.
> 
> I don't think it's sensitive - it just seems a bit sillier to send the same
> thing to the client twice than to the server log.

Ah, that adds weight to the benefit of LOG_SERVER_ONLY.

> I'm happy to change it to
> LOG if you prefer. Your points below mean some comments need to be updated in
> smgr/md.c anyway.

Nah.

> > > +/*
> > > + * smgrstartreadv() -- asynchronous version of smgrreadv()
> > > + *
> > > + * This starts an asynchronous readv IO using the IO handle `ioh`. Other than
> > > + * `ioh` all parameters are the same as smgrreadv().
> >
> > I would add a comment starting with:
> >
> >   Compared to smgrreadv(), more responsibilities fall on layers above smgr.
> >   Higher layers handle partial reads.  smgr will ereport(LOG_SERVER_ONLY) some
> >   problems, but higher layers are responsible for pgaio_result_report() to
> >   mirror that news to the user and (for ERROR) abort the (sub)transaction.
> 
> Hm - if we document that in all the smgrstart* we'd end up with something like
> that in a lot of places - but OTOH, this is the first one so far...

Alternatively, to avoid duplication:

  See $PLACE for the tasks that the caller's layer owns, in contrast to smgr
  owning them for smgrreadv().

> > I say "comment starting with", because I think there's a remaining decision
> > about who owns the zeroing currently tied to smgrreadv().  An audit of
> > mdreadv() vs. AIO counterparts found this part of mdreadv():
> >
> > 			if (nbytes == 0)
> > 			{
> > 				/*
> > 				 * We are at or past EOF, or we read a partial block at EOF.
> > 				 * Normally this is an error; upper levels should never try to
> > 				 * read a nonexistent block.  However, if zero_damaged_pages
> > 				 * is ON or we are InRecovery, we should instead return zeroes
> > 				 * without complaining.  This allows, for example, the case of
> > 				 * trying to update a block that was later truncated away.
> > 				 */
> > 				if (zero_damaged_pages || InRecovery)
> > 				{
> >
> > I didn't write a test to prove its absence, but I'm not finding such code in
> > the AIO path.
> 
> Yes, there is no such codepath
> 
> A while ago I had started a thread about whether the above codepath is
> necessary

postgr.es/m/3qxxsnciyffyf3wyguiz4besdp5t5uxvv3utg75cbcszojlz7p@uibfzmnukkbd
which I had forgotten completely.

I've redone your audit, and I agree the InRecovery case is dead code.
check-world InRecovery reaches mdstartreadv() and mdreadv() only via
XLogReadBufferExtended(), vm_readbuf(), and fsm_readbuf().

The zero_damaged_pages case entails more of a judgment call about whether or
not its rule breakage eclipses its utility.  Fortunately, a disappointed
zero_damaged_pages user could work around that code's absence by stopping the
server and using "dd" to extend the segment with zeros.

> I had planned to put in an error into mdreadv() at the time, but somehow lost
> track of that - I kind of mentally put this issue into the "done" category :(

> At the very least we need to add a comment about this though.

I'm fine with either of:

1. Replace that mdreadv() code with an error.

2. Update comment in mdreadv() that we're phasing out this code due the
   InRecovery case's dead code status and the zero_damaged_pages problems; AIO
   intentionally doesn't replicate it.  Maybe add Assert(false).

I'd do (2) for v18, then do (1) first thing in v19 development.

> > > +	*zeroed_or_error_count = rem_error & ((1 << 7) - 1);
> > > +	rem_error >>= 7;
> >
> > These raw "7" are good places to use your new #define values.  Likewise in
> > buffer_readv_encode_error().
> 
> Which define value are you thinking of here? I don't think any of the ones I
> added apply?  But I think you're right it'd be good to have some define for
> it, at least locally.

It was just my imagination.  Withdrawn.

> It's now:
> 
> /*
>  * We need a backend-local completion callback for shared buffers, to be able
>  * to report checksum errors correctly. Unfortunately that can only safely
>  * happen if the reporting backend has previously called
>  * pgstat_prepare_report_checksum_failure(), which we can only guarantee in
>  * the backend that started the IO. Hence this callback.
>  */

Sounds good.

> Updated to:
> 	/*
> 	 * Throw a WARNING/LOG, as instructed by PIV_LOG_*, if the checksum fails,
> 	 * but only after we've checked for the all-zeroes case.
> 	 */
> 
> I found one more, the newly added comment about checksum_failure_p was still
> talking about ignore_checksum_failure, but it should now be IGNORE_CHECKSUM_FAILURE.

That works.

> > > Subject: [PATCH v2.14 18/29] aio: Add test_aio module
> >
> > I didn't yet re-review the v2.13 or 2.14 changes to this one.  That's still in
> > my queue.
> 
> That's good - I think some of the tests need to expand a bit more. Since
> that's at the end of the dependency chain...

Okay, I'll delay on re-reviewing that one.  When it's a good time, please put
the CF entry back in Needs Review.  The patches before it are all ready for
commit after the above points of this mail.