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Re: pg_plan_advice

David G. Johnston <david.g.johnston@gmail.com>

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From: "David G. Johnston" <david.g.johnston@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Alexandra Wang <alexandra.wang.oss@gmail.com>, Richard Guo <guofenglinux@gmail.com>, Lukas Fittl <lukas@fittl.com>, Tom Lane <tgl@sss.pgh.pa.us>, Jacob Champion <jacob.champion@enterprisedb.com>, Dian Fay <di@nmfay.com>, Matheus Alcantara <matheusssilv97@gmail.com>, Jakub Wartak <jakub.wartak@enterprisedb.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-03-02T23:11:17Z
Lists: pgsql-hackers

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On Mon, Mar 2, 2026 at 3:09 PM David G. Johnston <david.g.johnston@gmail.com>
wrote:

> On Sun, Mar 1, 2026 at 9:10 PM David G. Johnston <
> david.g.johnston@gmail.com> wrote:
>
>> On Fri, Feb 27, 2026 at 6:16 PM David G. Johnston <
>> david.g.johnston@gmail.com> wrote:
>>
>>> On Fri, Feb 27, 2026 at 3:46 PM Robert Haas <robertmhaas@gmail.com>
>>> wrote:
>>>
>>>> On Thu, Feb 26, 2026 at 8:55 AM Robert Haas <robertmhaas@gmail.com>
>>>> wrote:
>>>> > Thanks, Alex, for the review.
>>>>
>>>> Here's v18. In addition to fixing the problems pointed out by Alex,
>>>> there are a couple of significant changes in this version.
>>>>
>>>>
>>> I have a mind to walk through the readmes and sgmls but its going to be
>>> in chunks.  Here's one for the readme for pg_plan_advice with a couple of
>>> preliminary sgml changes.
>>>
>>>
>> 0003 sgml focus with some readme.
>>
>>
> And now 0004 sgml (no readme):
>
>
Lastly, 0007 sgml (stash)

Placed entry in correct position on contrib page.

Expanded a bit on the security aspect comment.  I suppose there is some
indirect exposure via decisions being made implying table sizes or
records-per-FK...I left that unmentioned.

Added some explicit limitations to user-supplied values.

I would personally like to see "pg_set_stashed_advice" returning something
besides void.  I would usually go for text, but maybe in the interest of
i18n an integer would suffice.  +1 if a row was added, -1 if a row is
removed, or 0 for an update.  That would necessitate any other no-op being
an error.  Presently, supplying NULL for the query_id is not an error -
that seems like an oversight.  Same goes for supplying NULL for
stash_name.  If both of those cases produce errors (leaving NULL
advice_string being a remove indicator) the integer return seems like it
should work just fine.

Sorta feels like this module would appreciate advice strings having a
comment feature - so instead of just leaving an empty string behind saying
"we know, no advice needed" - it could contain actual content that isn't
applied advice.  Given the complexity of planning, comments seem warranted
in the advice themselves in any case.

Feels like this module needs export and import functions, especially given
the intro paragraph about the contents being volatile.  Or maybe a psql
script example producing a dynamic script file involving \gexec.

David J.

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. pg_plan_advice: Fix another unique-semijoin bug.

  2. pg_plan_advice: Export feedback-related definitions.

  3. pg_plan_advice: Fix a bug when a subquery is pruned away entirely.

  4. pg_plan_advice: Add alternatives test to Makefile.

  5. pg_plan_advice: Handle non-repeatable TABLESAMPLE scans.

  6. pg_stash_advice: Allow stashed advice to be persisted to disk.

  7. Add pg_stash_advice contrib module.

  8. pg_plan_advice: Avoid assertion failure with partitionwise aggregate.

  9. pg_plan_advice: Invent DO_NOT_SCAN(relation_identifier).

  10. Add an alternative_plan_name field to PlannerInfo.

  11. pg_plan_advice: Refactor to invent pgpa_planner_info

  12. Respect disabled_nodes in fix_alternative_subplan.

  13. get_memoize_path: Don't exit quickly when PGS_NESTLOOP_PLAIN is unset.

  14. test_plan_advice: Set TAP test priority 50 in meson.build.

  15. pg_plan_advice: Avoid a crash under GEQO.

  16. Test pg_plan_advice using a new test_plan_advice module.

  17. pg_plan_advice: Always install pg_plan_advice.h, and in the right place

  18. pg_plan_advice: Fix failures to accept identifier keywords.

  19. Add pg_plan_advice contrib module.

  20. Allow extensions to mark an individual index as disabled.

  21. Replace get_relation_info_hook with build_simple_rel_hook.

  22. Store information about Append node consolidation in the final plan.

  23. Store information about elided nodes in the final plan.

  24. Store information about range-table flattening in the final plan.

  25. Pass cursorOptions to planner_setup_hook.

  26. Fix PGS_CONSIDER_NONPARTIAL interaction with Materialize nodes.

  27. Fix mistakes in commit 4020b370f214315b8c10430301898ac21658143f

  28. Allow for plugin control over path generation strategies.

  29. Update some comments for fasthash

  30. Allow passing a pointer to GetNamedDSMSegment()'s init callback.

  31. Don't reset the pathlist of partitioned joinrels.

  32. Treat number of disabled nodes in a path as a separate cost metric.