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Re: pg_plan_advice

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Haibo Yan <tristan.yim@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-01-06T19:50:46Z
Lists: pgsql-hackers 
On Mon, Dec 29, 2025 at 6:34 PM Haibo Yan <tristan.yim@gmail.com> wrote:
> 1. GEQO interaction (patch 4):
> Since GEQO relies on randomized search, is there a risk that the optimizer may fail to explore the specific join order or path that is being enforced by the advice mask? In that case, could this lead to failures such as inability to construct the required join relation or excessive planning time if the desired path is not sampled?

The interaction of this feature with GEQO definitely needs more study.
If you have some time to work on this, I think testing and reporting
results would be quite useful. However, I don't think we should ever
get planner failure, and I'm doubtful about excessive planning time as
well. The effect of plan advice is to disable some paths just as if
enable_<whatever> were set to false, so if you provide very specific
advice while planning with GEQO, I think you might just end up with a
disabled path that doesn't account for the advice. However, this
should be checked, and I haven't gotten there yet. I'll add an XXX to
the README to make sure this doesn't get forgotten.

> 2. Parallel query serialization (patches 1–3):
> Several new fields (subrtinfos, elidedNodes, child_append_relid_sets) are added to PlannedStmt, but I did not see corresponding changes in outfuncs.c / readfuncs.c. Without serialization support, parallel workers executing subplans or Append nodes may not receive this metadata. Is this handled elsewhere, or is it something still pending?

I believe that gen_node_support.pl should take care of this
automatically unless the node type is flagged as
pg_node_attr(custom_read_write).

> 3. Alias handling when generating advice (patch 5):
> In pgpa_output_relation_name, the advice string is generated using get_rel_name(relid), which resolves to the underlying table name rather than the RTE alias. In self-join cases this could be ambiguous (e.g., my_table vs my_table). Would it be more appropriate to use the RTE alias when available?

No. That function is only used for indexes.

> 4. Minor typo (patch 4):
> In src/include/nodes/relation.h, parititonwise appears to be a typo and should likely be partitionwise.

Will fix, thanks.

-- 
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.