Re: Choosing values for multivariate MCV lists - Mailing list pgsql-hackers

From Dean Rasheed
Subject Re: Choosing values for multivariate MCV lists
Date
Msg-id CAEZATCVQYRScftGh-k_An8yo0d=GwNKzEUOR=t4g7Zw9Qd1=kQ@mail.gmail.com
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In response to Re: Choosing values for multivariate MCV lists  (Tomas Vondra <tomas.vondra@2ndquadrant.com>)
Responses Re: Choosing values for multivariate MCV lists  (Tomas Vondra <tomas.vondra@2ndquadrant.com>)
List pgsql-hackers
On Sat, 22 Jun 2019 at 15:10, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
> One annoying thing I noticed is that the base_frequency tends to end up
> being 0, most likely due to getting too small. It's a bit strange, though,
> because with statistic target set to 10k the smallest frequency for a
> single column is 1/3e6, so for 2 columns it'd be ~1/9e12 (which I think is
> something the float8 can represent).
>

Yeah, it should be impossible for the base frequency to underflow to
0. However, it looks like the problem is with mcv_list_items()'s use
of %f to convert to text, which is pretty ugly.

Regards,
Dean



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