Thread

Re: Wrong results with equality search using trigram index and non-deterministic collation

Zsolt Parragi <zsolt.parragi@percona.com> — 2026-05-07T19:00:04Z

Hello

> Does that mean that you could end up with wrong results (which would not
> be acceptable), or that you could end up with false positives that
> later get eliminated by the recheck (which would be fine)?

+ /*
+ * For non-C collations, extract the three bytes from each trigram
+ * and compare them using the collation's comparison function.
+ */

...

+ /* Use collation-aware comparison */
+ result = pg_strncoll(str_a, 3, str_b, 3, locale);
+ PG_RETURN_INT32(result);

For non-C collations, isn't the trigram likely a hash rather than a
proper string, where pg_strncoll won't work properly?