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JIRA issue: [SPARK-4570](https://issues.apache.org/jira/browse/SPARK-4570) We are planning to create a `BroadcastLeftSemiJoinHash` to implement the broadcast join for `left semijoin` In left semijoin : If the size of data from right side is smaller than the user-settable threshold `AUTO_BROADCASTJOIN_THRESHOLD`, the planner would mark it as the `broadcast` relation and mark the other relation as the stream side. The broadcast table will be broadcasted to all of the executors involved in the join, as a `org.apache.spark.broadcast.Broadcast` object. It will use `joins.BroadcastLeftSemiJoinHash`.,else it will use `joins.LeftSemiJoinHash`. The benchmark suggests these made the optimized version 4x faster when `left semijoin` <pre><code> Original: left semi join : 9288 ms Optimized: left semi join : 1963 ms </code></pre> The micro benchmark load `data1/kv3.txt` into a normal Hive table. Benchmark code: <pre><code> def benchmark(f: => Unit) = { val begin = System.currentTimeMillis() f val end = System.currentTimeMillis() end - begin } val sc = new SparkContext( new SparkConf() .setMaster("local") .setAppName(getClass.getSimpleName.stripSuffix("$"))) val hiveContext = new HiveContext(sc) import hiveContext._ sql("drop table if exists left_table") sql("drop table if exists right_table") sql( """create table left_table (key int, value string) """.stripMargin) sql( s"""load data local inpath "/data1/kv3.txt" into table left_table""") sql( """create table right_table (key int, value string) """.stripMargin) sql( """ |from left_table |insert overwrite table right_table |select left_table.key, left_table.value """.stripMargin) val leftSimeJoin = sql( """select a.key from left_table a |left semi join right_table b on a.key = b.key""".stripMargin) val leftSemiJoinDuration = benchmark(leftSimeJoin.count()) println(s"left semi join : $leftSemiJoinDuration ms ") </code></pre> Author: wangxiaojing <u9jing@gmail.com> Closes #3442 from wangxiaojing/SPARK-4570 and squashes the following commits: a4a43c9 [wangxiaojing] rebase f103983 [wangxiaojing] change style fbe4887 [wangxiaojing] change style ff2e618 [wangxiaojing] add testsuite 1a8da2a [wangxiaojing] add BroadcastLeftSemiJoinHash |
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