From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
---|---|
To: | Alexander Korotkov <aekorotkov(at)gmail(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Statistics and selectivity estimation for ranges |
Date: | 2012-08-06 14:09:09 |
Message-ID: | 501FD005.3020808@enterprisedb.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On 04.08.2012 12:31, Alexander Korotkov wrote:
> Hackers,
>
> attached patch is for collecting statistics and selectivity estimation for
> ranges.
>
> In order to make our estimations accurate for every distribution of
> ranges, we would collect 2d-distribution of lower and upper bounds of range
> into some kind of 2d-histogram. However, this patch use some simplification
> and assume distribution of lower bound and distribution of length to be
> independent.
Sounds reasonable. Another possibility would be to calculate the average
length for each lower-bound bin. So you would e.g know the average
length of values with lower bound between 1-10, and the average length
of values with lower bound between 10-20, and so forth. Within a bin,
you would have to assume that the distribution of the lengths is fixed.
PS. get_position() should guard against division by zero, when subdiff
returns zero.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
From | Date | Subject | |
---|---|---|---|
Next Message | Amit Kapila | 2012-08-06 14:23:44 | Re: WIP patch for LATERAL subqueries |
Previous Message | Amit Kapila | 2012-08-06 14:07:12 | Re: WIP patch for LATERAL subqueries |