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Re: pg_plan_advice

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Alexander Lakhin <exclusion@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Lukas Fittl <lukas@fittl.com>, Andrei Lepikhov <lepihov@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-04-06T19:52:51Z
Lists: pgsql-hackers 
On Sun, Apr 5, 2026 at 4:00 AM Alexander Lakhin <exclusion@gmail.com> wrote:
> I and SQLsmith have discovered one more anomaly (reproduced starting from
> e0e4c132e):
> load 'test_plan_advice';
> select object_type from
>   (select object_type from information_schema.element_types limit 1),
>   lateral
>   (select sum(1) over (partition by a) from generate_series(1, 2) g(a) where false);
>
> triggers an internal error:
> ERROR:  XX000: no rtoffset for plan unnamed_subquery
> LOCATION:  pgpa_plan_walker, pgpa_walker.c:110
>
> Could you please have a look?

Thanks for the report. What seems to be happening here is that the
whole query is replaced by a single Result node, since the join must
be empty. But that means that unnamed_subquery doesn't make it into
the final plan tree, and then pgpa_plan_walker() is sad about not
finding it. Normally it wouldn't care, but apparently this query
involves at least one semijoin someplace that the planner considered
converting into a regular join with one side made unique, so
pgpa_plan_walker() has an entry in sj_unique_rels and then wants to
adjust that entry for the final, flattened range table, and it can't.
I'm inclined to think that the fix is just:

-            elog(ERROR, "no rtoffset for plan %s", proot->plan_name);
+            continue;

...plus a comment update, but I want to spend some time mulling over
whether that might break anything else before I go do 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.