[ https://issues.apache.org/jira/browse/SPARK-17074?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Zhenhua Wang updated SPARK-17074: --------------------------------- Description: 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. We first use [SPARK-18000] and [SPARK-17881] to compute equi-width histograms (for both numeric and string types) or endpoints of equi-height histograms (for numeric type only). Then, if we get endpoints of a equi-height histogram, we need to compute ndv's between those endpoints by [SPARK-17997] to form the equi-height histogram. This Jira incorporates three Jiras mentioned above to support needed aggregation functions. We need to resolve them before this one. was: 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. > 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. > We first use [SPARK-18000] and [SPARK-17881] to compute equi-width histograms (for both numeric and string types) or endpoints of equi-height histograms (for numeric type only). Then, if we get endpoints of a equi-height histogram, we need to compute ndv's between those endpoints by [SPARK-17997] to form the equi-height histogram. > This Jira incorporates three Jiras mentioned above to support needed aggregation functions. We need to resolve them before this one. -- This message was sent by Atlassian JIRA (v6.3.4#6332) --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscribe@spark.apache.org For additional commands, e-mail: issues-help@spark.apache.org