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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: Jakub Wartak <jakub.wartak@enterprisedb.com>, Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-04-07T14:17:12Z
Lists: pgsql-hackers 
On Sat, Apr 4, 2026 at 4:12 AM Lukas Fittl <lukas@fittl.com> wrote:
> I think we should document the restrictions on advice names here (i.e.
> they must be alphanumeric or contain an underscore, not start with a
> digit, and maximum NAMEDATLEN).

I committed 0001 without this change. Please feel free to propose a
clean-up patch that adds this. I wasn't certain where the best place
to add it was, or what the wording ought to be exactly.

> > +/*
> > + * Remove all stashes and entries from shared memory.
> > + *
> > + * This is intended to be called before reloading from a dump file, so that
> > + * a failed previous attempt doesn't leave stale data behind.
> > + */
> > +void
> > +pgsa_reset_all_stashes(void)
> > +{
>
> I think this might be good to expose on the SQL level as well - in
> case someone accidentally created a lot of stashes it could be tedious
> to remove them all, e.g. if they wanted to clear all the memory after
> an experiment.

From SQL, you can just do select pg_drop_advice_stash(stash_name) from
pg_get_advice_stashes(), which seems good enough to me. If there's a
compelling reason to have more than that, we can think about it, but I
don't particularly see one, and having fewer exposed entrypoints is
better, ceteris paribus. One disadvantage of that approach is that if
it fails due to some concurrency issue, then you might end up with
some stashes dropped and others not, but I don't see this as being
such a frequent operation that it should really cause an issue.

> > diff --git a/contrib/pg_stash_advice/stashpersist.c b/contrib/pg_stash_advice/stashpersist.c
> > new file mode 100644
> > index 00000000000..da96ee0d803
> > --- /dev/null
> > +++ b/contrib/pg_stash_advice/stashpersist.c
> >...
> > +            /* Parse the query ID. */
> > +            errno = 0;
> > +            queryId = strtoll(queryid_str, &endptr, 10);
> > +            if (*endptr != '\0' || errno != 0 || queryid_str == endptr)
> > +                ereport(ERROR,
> > +                        (errcode(ERRCODE_DATA_CORRUPTED),
> > +                         errmsg("syntax error in file \"%s\" line %u: invalid query ID \"%s\"",
> > +                                PGSA_DUMP_FILE, lineno, queryid_str)));
> > +
>
> It might be worth adding a queryId == 0 check here, since we won't
> check it later, and its helpful to avoid unpredictable behavior just
> in case someone decided to mess with the file manually.

Good point. Added that and committed 0002. I also changed the
write-to-the-persist file path to take only shared locks instead of
exclusive, since the latter seems unnecessary.

-- 
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.