On Sat, 7 Nov 2026 at 21:07, PG Bug reporting form <noreply(at)postgresql(dot)org>
wrote:
> The following bug has been logged on the website:
>
> Bug reference: 19849
> Logged by: Atish Prakash
> Email address: 125atishprak(at)gmail(dot)com
> PostgreSQL version: 18.6
> Operating system: Linux x86_64
> Description:
>
> With extended statistics on an array or tsvector expression, once ANALYZE
> finds no
> elements common enough to store, queries that use the statistics fail at
> planning
> time with an internal error. Elements that are all distinct are enough to
> trigger
> this, as is a column of empty arrays.
>
> CREATE TABLE tags(id int, a int[]);
> INSERT INTO tags
> SELECT i, ARRAY[i, i + 1000000] FROM generate_series(1, 50000) i;
> CREATE STATISTICS s_a ON (a || a) FROM tags;
> ANALYZE tags;
>
> SELECT count(*) FROM tags WHERE (a || a) @> '{5}';
>
> Actual, on 19rc1 and master:
>
> ERROR: unexpected null value in cached tuple for catalog pg_statistic
> column stavalues3
>
> Expected, as on 18.6: the query runs and returns 1.
>
> Also failing the same way:
> - (t || t) on text[], with @>
> - (v || v) on tsvector, with @@ (the message names stavalues1)
> - the array operators && and <@, and = ANY
>
> A range expression with no non-empty values also stores a NULL stavalues,
> but the
> query I tried, (a * a) && '[1,2)', did not fail.
>
> A plain column with the same data, and an expression index with the same
> data, do
> not fail.
>
> Cause: commit 261f89a976 ("Track the maximum possible frequency of non-MCE
> array
> elements") stores a statistics slot even when there are no values. It
> changed the
> test in update_attstats() from numvalues > 0 to stavalues != NULL, but
> serialize_expr_stats() in extended_stats.c still tests numvalues[k] > 0, so
> the slot
> kind and numbers are stored with a NULL stavalues. get_attstatsslot() then
> fails in
> SysCacheGetAttrNotNull(). I identified the commit from the code and the
> commit
> message, and did not bisect.
>
> A possible patch is attached
> (0001-fix-expression-stats-empty-stavalues.patch). It
> changes that test to match update_attstats(). With it, the queries above
> return
> correct results on master, and all 239 core regression tests pass. It adds
> no new
> test.
>
> Found with statistics round-trip tests. I reproduced and checked the result
> myself.
>
>
>