On 5 September 2015 at 20:46, Bruce Momjian <bruce@momjian.us> wrote:
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.
Glad to see you agree.
Why have you said this on *this* patch, when Tomas' patch has been very obviously addressing this problem since January, with very little traction.
Please add your backing to Tomas' patch.
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Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
