RE: Histograms - When were they last created?

Siva,

Buckets are the groupings used to collect statistics for histograms. See the following excerpt
from Metalink note 35453.1

12.4.1 Height-Balanced Histograms

Oracle's histograms are height balanced (as opposed to width balanced). Width-balanced histograms divide the data into a fixed number of equal-width ranges and then count the number of values falling into each range. Height-balanced histograms place the same number of values into each range so that the endpoints of the range are determined by how many values are in that range.

For example, suppose that the values in a single column of a 1000-row table range between 1 and 100, and suppose that you want a 10-bucket histogram (ranges in a histogram are often referred to as "buckets"). In a width-balanced histogram, the buckets would be of equal width (1-10, 11-20, 21,-30, etc.) and each bucket would count the number of rows that fall into that range. In a height-balanced histogram, each bucket has the same height (in this case 100 rows), and then the endpoints for the buckets would be determined by the density of the distinct values in the column.

Hope this helps, Received on Wed Aug 16 2000 - 07:32:15 CDT