On 8/12/21 4:26 AM, Tomas Vondra wrote:
> On 8/11/21 2:48 AM, Peter Geoghegan wrote:
>> On Wed, Jun 23, 2021 at 7:19 AM Andrey V. Lepikhov
>> <a.lepikhov@postgrespro.ru> wrote:
>>> Ivan Frolkov reported a problem with choosing a non-optimal index during
>>> a query optimization. This problem appeared after building of an
>>> extended statistics.
>>
>> Any thoughts on this, Tomas?
>>
>
> Thanks for reminding me, I missed / forgot about this thread.
>
> I agree the current behavior is unfortunate, but I'm not convinced the
> proposed patch is fixing the right place - doesn't this mean the index
> costing won't match the row estimates displayed by EXPLAIN?
I think, it is not a problem. In EXPLAIN you will see only 1 row
with/without this patch.
>
> I wonder if we should teach clauselist_selectivity about UNIQUE indexes,
> and improve the cardinality estimates directly, not just costing for
> index scans.
This idea looks better. I will try to implement it.
>
> Also, is it correct that the patch calculates num_sa_scans only when
> (numIndexTuples >= 0.0)?
Thanks, fixed.
--
regards,
Andrey Lepikhov
Postgres Professional
