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Re: pg_plan_advice

Alexandra Wang <alexandra.wang.oss@gmail.com>

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From: Alexandra Wang <alexandra.wang.oss@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Lukas Fittl <lukas@fittl.com>, Jacob Champion <jacob.champion@enterprisedb.com>, Dian Fay <di@nmfay.com>, Matheus Alcantara <matheusssilv97@gmail.com>, Jakub Wartak <jakub.wartak@enterprisedb.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-02-02T19:36:47Z
Lists: pgsql-hackers 
Hi Robert,

On Wed, Jan 28, 2026 at 9:14 AM Robert Haas <robertmhaas@gmail.com> wrote:

> Thanks to all who have reviewed so far, and please keep it coming. I
> am especially in need of more code review at this point.
>

Thanks for the patches! I’ve reviewed 0001 - 0003 so far; here are my
comments.

0001:
The code looks good to me. However, I feel a bit uneasy about not
seeing a test case for the additional subplan origin display added in
pg_overexplain. Maybe we could add the following test cases to
exercise that code:

-- should show "Subplan: sub"
EXPLAIN (RANGE_TABLE, COSTS OFF)
SELECT * FROM vegetables v,
       (SELECT * FROM vegetables WHERE genus = 'daucus' OFFSET 0) sub;

-- should show "Subplan: unnamed_subquery"
EXPLAIN (RANGE_TABLE, COSTS OFF)
SELECT * FROM vegetables v,
       (SELECT * FROM vegetables WHERE genus = 'daucus' OFFSET 0);

0002:
Looks good to me.

0003:
I see code like this:

@@ -2232,6 +2251,11 @@ accumulate_append_subpath(Path *path, List
**subpaths, List **special_subpaths)
  if (!apath->path.parallel_aware || apath->first_partial_path == 0)
  {
  *subpaths = list_concat(*subpaths, apath->subpaths);
+ *child_append_relid_sets =
+ lappend(*child_append_relid_sets, path->parent->relids);
+ *child_append_relid_sets =
+ list_concat(*child_append_relid_sets,
+ apath->child_append_relid_sets);

in accumulate_append_subpath(), but in get_singleton_append_subpath()
there are only calls to lappend() and no list_concat(). Is that
intentional? Do we also want to concatenate the newly pulled up
child_append_relid_sets with the existing ones in
get_singleton_append_subpath()?

In add_paths_to_append_rel():

@@ -1785,13 +1790,16 @@ add_paths_to_append_rel(PlannerInfo *root,
RelOptInfo *rel,
        {
            Path       *path = (Path *) lfirst(l);
            AppendPath *appendpath;
+           AppendPathInput append = {0};
+
+           append.partial_subpaths = list_make1(path);
+           append.child_append_relid_sets = list_make1(rel->relids);

Could you help me understand why we need to populate
append.child_append_relid_sets here? I don’t see this child rel being
pulled up at this point.

0004:
I’ve only read through the README and documentation so far; I’ll
continue reviewing the code in 0004.

Best,
Alex

-- 
Alexandra Wang
EDB: https://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.