Re: Choosing values for multivariate MCV lists

From: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Choosing values for multivariate MCV lists
Date: 2019-06-23 19:48:26
Message-ID: CAEZATCVQYRScftGh-k_An8yo0d=GwNKzEUOR=t4g7Zw9Qd1=kQ@mail.gmail.com
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-hackers

On Sat, 22 Jun 2019 at 15:10, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)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

In response to

Responses

Browse pgsql-hackers by date

  From Date Subject
Next Message Peter Eisentraut 2019-06-23 19:55:47 Re: using explicit_bzero
Previous Message Peter Eisentraut 2019-06-23 19:44:15 Re: how to run encoding-dependent tests by default