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
