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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