liupc commented on issue #23438: [SPARK-26525][SHUFFLE]Fast release ShuffleBlockFetcherIterator on completion of the iteration URL: https://github.com/apache/spark/pull/23438#issuecomment-459600935 @cloud-fan I verified this patch with some hacked code, it does work well. ``` override def compute(partition: Partition, context: TaskContext): Iterator[T] = { partition.asInstanceOf[CoalescedRDDPartition].parents.iterator.flatMap { parentPartition => if (parentPartition.index != partition.asInstanceOf[CoalescedRDDPartition].parents.head.index) { logInfo(s"First parent iterator already exhausted, just wait for heap dump...") Thread.sleep(Long.MaxValue) } firstParent[T].iterator(parentPartition, context) } } ``` First, start a spark-shell app ``` liupengcheng@dev:~/work/git/github-me/spark/bin$ ./spark-shell --master local-cluster[1,1,1024] 19/02/01 12:04:48 WARN Utils: Your hostname, dev resolves to a loopback address: 127.0.1.1; using 10.239.35.194 instead (on interface eno1) 19/02/01 12:04:48 WARN Utils: Set SPARK_LOCAL_IP if you need to bind to another address 19/02/01 12:04:49 WARN NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable Using Spark's default log4j profile: org/apache/spark/log4j-defaults.properties Setting default log level to "WARN". To adjust logging level use sc.setLogLevel(newLevel). For SparkR, use setLogLevel(newLevel). Spark context Web UI available at http://10.239.35.194:4040 Spark context available as 'sc' (master = local-cluster[1,1,1024], app id = app-20190201120456-0000). Spark session available as 'spark'. Welcome to ____ __ / __/__ ___ _____/ /__ _\ \/ _ \/ _ `/ __/ '_/ /___/ .__/\_,_/_/ /_/\_\ version 3.0.0-SNAPSHOT /_/ Using Scala version 2.12.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_144) Type in expressions to have them evaluated. Type :help for more information. scala> sc.parallelize((1 to 1000), 1000).repartition(1000).coalesce(1).collect() [Stage 1:> (0 + 1) / 1] ``` Second, when sleep at the hacked code, then do heapdump. `jmap -dump:alive,format=b,file=./a.hrpof 22551` // Notice that the `alive` would trigger full gc before heapdump Third, use visualVm to check the ShuffleBlockFetcherIterator refcount in the heap. 
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