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

From: Tomek <tomekphotos(at)gmail(dot)com>
To: "aokulovich(at)stiltsoft(dot)com" <aokulovich(at)stiltsoft(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Postgres 15 SELECT query doesn't use index under RLS
Date: 2023-10-19 07:43:44
Message-ID: CACUaW3RUoQu6i7LHUOPe3Rg28AzTc052GH-Pn1fK1+nZaukQ7A@mail.gmail.com
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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
>>
>

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