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

[Tomek]

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
>>
>

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

[Alexander Okulovich]

Hi Tomek,

Unfortunately, I didn't dig into this. This request is recommended to 
provide when describing 
 
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