Horton

Re: AIO v2.5

Melanie Plageman <melanieplageman@gmail.com>

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From: Melanie Plageman <melanieplageman@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Antonin Houska <ah@cybertec.at>, Noah Misch <noah@leadboat.com>, 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: 2025-03-19T17:20:17Z
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 aio: Fix reference to outdated name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, Mar 18, 2025 at 4:12 PM Andres Freund <andres@anarazel.de> wrote:
>
> Attached is v2.10,

I noticed a few comments could be improved in  0011: bufmgr: Use AIO
in StartReadBuffers()

In WaitReadBuffers(), this comment is incomplete:

        /*
-        * Skip this block if someone else has already completed it.  If an
-        * I/O is already in progress in another backend, this will wait for
-        * the outcome: either done, or something went wrong and we will
-        * retry.
+        * If there is an IO associated with the operation, we may need to
+        * wait for it. It's possible for there to be no IO if
         */

In WaitReadBuffers(), too many thes

        /*
         * Most of the the the one IO we started will read in everything.  But
         * we need to deal with short reads and buffers not needing IO
         * anymore.
         */

In ReadBuffersCanStartIO()

+       /*
+        * Unfortunately a false returned StartBufferIO() doesn't allow to
+        * distinguish between the buffer already being valid and IO already
+        * being in progress. Since IO already being in progress is quite
+        * rare, this approach seems fine.
+        */

maybe reword "a false returned StartBufferIO()"

Above and in AsyncReadBuffers()

 * To support retries after short reads, the first operation->nblocks_done is
 * buffers are skipped.

can't quite understand this

+ * On return *nblocks_progres is updated to reflect the number of buffers
progress spelled wrong

     * A secondary benefit is that this would allows us to measure the time in
     * pgaio_io_acquire() without causing undue timer overhead in the common,
     * non-blocking, case.  However, currently the pgstats infrastructure
     * doesn't really allow that, as it a) asserts that an operation can't
     * have time without operations b) doesn't have an API to report
     * "accumulated" time.
     */

allows->allow

What would the time spent in pgaio_io_acquire() be reported as? Time
submitting IOs? Time waiting for a handle? And what is "accumulated"
time here? It seems like you just add the time to the running total
and that is already accumulated.

- Melanie