[jira] [Created] (SPARK-17074) generate histogram information for column

["Ron Hu (JIRA)" <ji...@apache.org>]

Ron Hu created SPARK-17074:
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             Summary: generate histogram information for column
                 Key: SPARK-17074
                 URL: https://issues.apache.org/jira/browse/SPARK-17074
             Project: Spark
          Issue Type: Sub-task
          Components: Optimizer
    Affects Versions: 2.0.0
            Reporter: Ron Hu


We support two kinds of histograms: 
-	Equi-width histogram: We have a fixed width for each column interval in the histogram.  The height of a histogram represents the frequency for those column values in a specific interval.  For this kind of histogram, its height varies for different column intervals. We use the equi-width histogram when the number of distinct values is less than 254.
-	Equi-height histogram: For this histogram, the width of column interval varies.  The heights of all column intervals are the same.  The equi-height histogram is effective in handling skewed data distribution. We use the equi- height histogram when the number of distinct values is equal to or greater than 254.  




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