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Re: pg_plan_advice

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Lukas Fittl <lukas@fittl.com>, 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: 2026-01-08T23:29:38Z
Lists: pgsql-hackers 
On Thu, Jan 08, 2026 at 11:07:31AM -0500, Robert Haas wrote:
> On Wed, Jan 7, 2026 at 2:04 AM Lukas Fittl <lukas@fittl.com> wrote:
>> That said, good news: After a bunch of iterations, I get a clean
>> pass on the pg_hint_plan regression tests, whilst completely
>> dropping its copying of core code and hackish re-run of
>> set_plain_rel_pathlist. See [0] for a draft PR (on my own fork of
>> pg_hint_plan) with individual patches that explain some regression
>> test differences.
> 
> That sounds AWESOME.

So you are telling me that I can commit code that deletes code.  Count
me in.  The project has some merge requests that I've been holding on
a bit due to what's happening here and because I did not really look
at the internals that have changed.  It's great to see that you have
begun an investigation, Lukas.

>> The biggest change in the regression test output was due to how the
>> "Parallel" hint worked in pg_hint_plan (basically it was setting
>> parallel_*_cost to zero, and then messed with the gucs that factor
>> into compute_parallel_worker) -- I think the only sensible thing to
>> do is to change that in pg_hint_plan, and instead rely on rejecting
>> non-partial paths with PGS_CONSIDER_NONPARTIAL if "hard"
>> enforcement of parallelism is requested. That caused some minor
>> plan changes, but I think they can still be argued to be matching
>> the user's intent of "make a scan involving this relation
>> parallel".
> 
> Cool. I'm sort of curious what changed, but maybe it's not important
> enough to spend time discussing right now.

I suspect that this is going to be an incremental integration process,
and it smells to me that it is going to require more than one major
release before being able to remove the whole set of hacks that
pg_hint_plan has been using, particularly with the GUCs, the costing
and the forced update of the backend routines which is a ugly
historical hack.  Saying that, I would need to look at the plan
outputs to be sure, perhaps we would be OK even with slight changes.
These happen every year, because the plans tested are complex enough
that some of the sub-paths are changed, but the hints still work
properly.  This year for v19 we have at least the changes in the
expression names.
--
Michael

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.