Re: Postgres 15 SELECT query doesn't use index under RLS

Hi Tomek,

Unfortunately, I didn't dig into this. This request is recommended to 
provide when describing 
<https://wiki.postgresql.org/wiki/Slow_Query_Questions#Statistics:_n_distinct,_MCV,_histogram> 
slow query issues, but looks like it relates to JOINs in the query, 
which we don't have.

Kind regards,

Alexander

On 19.10.2023 09:43, Tomek wrote:
> Hi Alexander!
> Apart from the problem you are writing about I'd like to ask you to 
> explain how you interpret counted frac_MCV - for me it has no sense at 
> all to summarize most_common_freqs.
> Please rethink it and explain what was the idea of such SUM ? I 
> understand that it can be some measure for ratio of NULL values but 
> only in some cases when n_distinct is small.
>
> regards
>
>>
>>               Statistics: n_distinct, MCV, histogram
>>
>>         Useful to check statistics leading to bad join plan. SELECT
>>         (SELECT sum(x) FROM unnest(most_common_freqs) x) frac_MCV,
>>         tablename, attname, inherited, null_frac, n_distinct,
>>         array_length(most_common_vals,1) n_mcv,
>>         array_length(histogram_bounds,1) n_hist, correlation FROM
>>         pg_stats WHERE attname='...' AND tablename='...' ORDER BY 1
>>         DESC;
>>
>>         Returns 0 rows.
>>
>>
>>         Kind regards,
>>
>>         Alexander
>>