Xianyang Liu created SPARK-21923:
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Summary: 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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