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
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