From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Multi-column distinctness. |
Date: | 2015-09-05 19:46:42 |
Message-ID: | 20150905194642.GB3133@momjian.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Fri, Aug 28, 2015 at 05:33:34PM +0900, Kyotaro HORIGUCHI wrote:
> Hello, this patch enables planner to be couscious of inter-column
> correlation.
>
> Sometimes two or more columns in a table has some correlation
> which brings underestimate, which leads to wrong join method and
> ends with slow execution.
>
> Tomas Vondra is now working on heavily-equipped multivariate
> statistics for OLAP usage. In contrast, this is a lightly
> implemented solution which calculates only the ratio between a
> rows estimated by current method and a actual row number. I think
> this doesn't conflict with his work except the grammar part.
I am very glad multi-variate statistics are being addressed. I think
this is our most common cause of optimizer failures.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2015-09-05 20:05:02 | Re: Fix small bug for build without HAVE_SYMLINK |
Previous Message | dinesh kumar | 2015-09-05 19:45:09 | Re: [PATCH] SQL function to report log message |