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Re: pg_plan_advice

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Lukas Fittl <lukas@fittl.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-03-26T17:20:21Z
Lists: pgsql-hackers

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On Thu, Mar 26, 2026 at 9:55 AM Robert Haas <robertmhaas@gmail.com> wrote:
> Whoops. Obviously got the wrong thing stuck in my cut and paste buffer
> when I was writing that. Thanks for checking it. I'm going to go ahead
> and commit this, because I'm pretty confident that it's correct, and
> the rest of these patches are not going to fix the buildfarm
> instability without it, and I'm pretty sure multiple committers are
> pretty tired of seeing these test_plan_advice failures already.

Done.

> Right, the comment isn't quite correct. I don't think your rewording
> is quite right either, though, because there's really no reason to
> mention plan_name here at all. I'll adjust it.

Done and committed, after also adjusting the memory context handling
to avoid re-breaking GEQO.

> The dangling pointers are a good point; I agree that's bad. However,
> I'd be more inclined to fix it by nulling out the alternative_root
> pointers at the end of set_plan_references. I think that would just be
> the case where root->isAltSubplan[ndx] && root->isUsedSubplan[ndx].
> The reason I'm reluctant to just store the name is that there's not an
> easy way to find a PlannerInfo by name. I originally proposed an
> "allroots" list in PlannerGlobal, but we went with subplanNames on
> Tom's suggestion. I subsequently realized that this kind of stinks for
> code that is trying to use this infrastructure for anything, for
> exactly this reason, but Tom never responded and I never pressed the
> issue. But I think we're boxing ourselves into a corner if we just
> keep storing names that can't be looked up everywhere. It doesn't
> matter for the issue before us, so maybe doing as you say here is the
> right idea just so we can move forward, but I think we're probably
> kidding ourselves a little bit.

Here's a new version, where I've replaced alternative_root by
alternative_plan_name, serving the same function.

-- 
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.