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Re: pg_plan_advice

Andrei Lepikhov <lepihov@gmail.com>

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From: Andrei Lepikhov <lepihov@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>
Cc: Alexander Lakhin <exclusion@gmail.com>, Lukas Fittl <lukas@fittl.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-04-04T09:34:35Z
Lists: pgsql-hackers 
On 4/4/26 05:14, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> The terms that I'm thinking in are "how much redesign will we accept
> post-feature-freeze, in either pg_plan_advice or test_plan_advice,
> before choosing to revert those modules entirely for v19?".  I think
> that running those tests serially is a sufficiently low-risk option
> that it'd be okay to put it in post-freeze, even very long after.
> I'm not sure that any of the other group-1 or group-2 options you
> suggested would be okay post-freeze.  (Of course, ultimately that'd
> be the RMT's decision not mine.)
> 
> I believe that we probably will need to do something in this
> area before v19 release.  If we're willing to commit to it being
> "run the tests serially", then sure we can wait awhile before
> actually doing that.  Maybe we'll even think of a better idea
> ... but what we can do about this post-freeze seems pretty
> constrained to me.

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

-- 
regards, Andrei Lepikhov,
pgEdge

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.