Horton
Menu

Re: pg_plan_advice

Robert Haas <robertmhaas@gmail.com>

View thread
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: 2026-04-04T22:52:21Z
Lists: pgsql-hackers 
On Sat, Apr 4, 2026 at 5:02 PM Andrei Lepikhov <lepihov@gmail.com> wrote:
> That’s exactly what concerns me. I see it as a potential design flaw if
> the extension has to make assumptions about possible plan configurations.
> I’m not sure how it works in detail, of course. However, when I designed
> Postgres replanning in the past, and made similar core changes to what
> you’ve done for pg_plan_advice, this kind of problem couldn’t have
> happened. So, I think it’s worth questioning the current approach and
> looking for other options.

I mean, any plan stability feature is intrinsically tied to a
particular planner. Nobody thinks you can use Aurora Postgres's Query
Plan Management feature with MySQL or DB2 or Oracle. Those products
obviously have to have their own features for plan stability. The same
is true here. There's more overlap because you're creating the plan
out of the same basic building blocks rather than an entirely
different set of things, but if you assemble them in a way that
PostgreSQL doesn't, then some things may not work. pg_plan_advice is
one of those things; the executor is another. Of course, I don't think
anybody here is keen to break stuff for no good reason, which is why I
will take a look at the report you posted. But fundamentally, it's the
same issue. If somebody uses a plugin that replaces large parts of the
plan with a CustomScan, pg_plan_advice isn't going to work with that,
either: how could it possibly? Maybe there could be some way to make
pg_plan_advice pluggable so that if extensions fiddle with the planner
they can also do matching fiddling with pg_plan_advice if they're so
inclined, but having it "just work" would require magic.

-- 
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.