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Zhenhua Wang edited comment on SPARK-17074 at 10/13/16 12:55 AM: ----------------------------------------------------------------- Well, I've got stuck here for a few days. I went through the QuantileSummaries paper and our code in Spark, and I still don't have any clue how to implement the second method and get its bounds. So I decide to adopt the first method for now, such that it won't block our progress on CBO work. We can implement the other one in the future. A PR for a new agg function for string histogram (equi-width) is already sent. I'll start to work on this one today and send a pr in the following days. Thanks! was (Author: zenwzh): Well, I've got stuck here for a few days. I went through the QuantileSummaries paper and our code in Spark, and I still don't have any clue how to implement the second method and get its bounds. So I decide to adopt the first method for now, such that it won't block our progress on CBO work. We can implement the other one in the future. A PR for a new agg function for string histogram is already sent. I'll start to work on this one today and send a pr in the following days. Thanks! > 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. -- This message was sent by Atlassian JIRA (v6.3.4#6332) --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@spark.apache.org For additional commands, e-mail: issues-h...@spark.apache.org