Re: Dump statistic issue with index on expressions

Hi, Maksim!

On Wed, May 20, 2026 at 12:52 PM Maksim.Melnikov
<m(dot)melnikov(at)postgrespro(dot)ru> wrote:
> On 5/11/26 02:42, Alexander Korotkov wrote:
> > On Wed, Feb 25, 2026 at 6:37 PM Maksim.Melnikov
> > <m(dot)melnikov(at)postgrespro(dot)ru> wrote:
> >> There is an issue on new feature dump statistics related to index
> >> processing.
> >> In case when table has more then one index and if one of them is index
> >> on expressions
> >> we can get error like this:
> >>
> >> pg_dump --verbose --statistics-only > /dev/null
> >> ...
> >> pg_dump: reading subscriptions
> >> pg_dump: reading subscription membership of tables
> >> pg_dump: reading dependency data
> >> pg_dump: saving encoding = UTF8
> >> pg_dump: saving "standard_conforming_strings = on"
> >> pg_dump: saving "search_path = "
> >> pg_dump: error: could not find index attname "source_system"
> >>
> >> For clarity, schema ddl attached
> >>
> >> CREATE TABLE test_table_stats (
> >> id uuid NOT NULL,
> >> body jsonb,
> >> source_system character varying,
> >> source_id character varying,
> >> model_name character varying NOT NULL
> >> );
> >>
> >> CREATE INDEX test_table_stats_source_system_text ON test_table_stats
> >> USING btree (upper((source_system)::text));
> >> CREATE UNIQUE INDEX test_table_stats_json_system_un ON test_table_stats
> >> USING btree (source_system, source_id, model_name);
> >>
> >> When pg_dump sequentially process indexes in case when index is
> >> processed after index on expression,
> >> it can use index attrs names of previously processed index. I've
> >> attached simple patch to fix it.
> > I see this is a bug indeed: an index with no expression can get its
> > indAttNames and nindAttNames from the previous index. But I didn't
> > manage to reproduce your case. dumpRelationStats_dumper() only
> > iterates indexes with pg_stats entry, and those are indexes with
> > expressions. Could you give more details on how did you reproduce
> > user-facing error? Which particular git commit did you use? How did
> > you fill the database step by step?
> >
> > ------
> > Regards,
> > Alexander Korotkov
> > Supabase
> >
> >
> Sorry for delay, I've tried to reproduce this issue for some time and
> detect that it isn't reproducable on vanilla postgresql.
> It seems, that our fork generate more records for pg_statistics unlike
> vanilla, that generate records only for indexes with expressions,
> more details can be found here in src/backend/commands/analyze.c
>
> static void
> do_analyze_rel(Relation onerel, VacuumParams *params,
> List *va_cols, AcquireSampleRowsFunc acquirefunc,
> BlockNumber relpages, bool inh, bool in_outer_xact,
> int elevel)
> {
> ......
> thisdata->tupleFract = 1.0; /* fix later if partial */
> if (indexInfo->ii_Expressions != NIL && va_cols == NIL)
> {
> ListCell *indexpr_item =
> list_head(indexInfo->ii_Expressions);
>
> thisdata->vacattrstats = (VacAttrStats **)
> palloc(indexInfo->ii_NumIndexAttrs *
> sizeof(VacAttrStats *));
> .....
> thisdata->attr_cnt = tcnt;
>
>
> Anyway, it seems code, reported before, isn't ideal and prone to bugs.
> In my opinion better fix it.
> Hope it will be helpful.

Thank you. Now this is clear. No user-facing error, but an internal
inconsistency. I'm going to push (and backpatch) this after release
freeze is lifted.

------
Regards,
Alexander Korotkov
Supabase