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Re: pg_plan_advice

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Andrei Lepikhov <lepihov@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Alexander Lakhin <exclusion@gmail.com>, Lukas Fittl <lukas@fittl.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-04-04T18:42:19Z
Lists: pgsql-hackers 
On Sat, Apr 4, 2026 at 5:34 AM Andrei Lepikhov <lepihov@gmail.com> wrote:
> As you work on the code, please keep the pg_plan_advice issue [1] in
> mind. I came across it while designing the optimisation in [2]. Even if
> [2] is not added to the Postgres core, this still looks like a valid
> query plan and may be proposed by an extension. So, the hinting module
> should avoid conflicts with other extensions, just as pg_hint_plan does.
>
> [1] pg_plan_advice fails when NestLoop outer side is Sort over FunctionScan
> https://www.postgresql.org/message-id/78dd9572-7569-4025-984d-e07d7f381b6e@gmail.com
> [2] Try a presorted outer path when referenced by an ORDER BY prefix
> https://www.postgresql.org/message-id/19a9265c-c441-4a43-bc0d-dac533438da0%40gmail.com

I'll take a look at that issue when I have a free moment. We certainly
cannot promise in general that pg_plan_advice will be able to make
sense of plans that PostgreSQL's own planner does not produce; that
would require magical code. But there might be something that can be
done to ameliorate this particular instance.

By the way, I'm really glad you hit that error. That particular error
check is there precisely to find plans that pg_plan_advice isn't able
to understand, and it sounds like it is doing its job as intended.
Having problems isn't great, but knowing that you have problems is a
lot better than still having them but not knowing about it.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

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.