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https://issues.apache.org/jira/browse/SPARK-21923?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Apache Spark reassigned SPARK-21923:
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Assignee: (was: Apache Spark)
> Avoid call reserveUnrollMemoryForThisTask every record
> ------------------------------------------------------
>
> Key: SPARK-21923
> URL: https://issues.apache.org/jira/browse/SPARK-21923
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Affects Versions: 2.2.0
> Reporter: Xianyang Liu
>
> When Spark persist data to Unsafe memory, we call the method
> `MemoryStore.putIteratorAsValues`, which need synchronize the `memoryManager`
> for every record write. This implementation is not necessary, we can apply
> for more memory at a time to reduce unnecessary synchronization.
> Test case:
> ```scala
> val start = System.currentTimeMillis()
> val data = sc.parallelize(0 until Integer.MAX_VALUE, 100)
> .persist(StorageLevel.OFF_HEAP)
> .count()
> println(System.currentTimeMillis() - start)
> ```
> Test result:
> before
> | 27647 | 29108 | 28591 | 28264 | 27232 |
> after
> | 26868 | 26358 | 27767 | 26653 | 26693 |
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