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https://issues.apache.org/jira/browse/SPARK-18231?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15728425#comment-15728425
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Apache Spark commented on SPARK-18231:
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User 'a-roberts' has created a pull request for this issue:
https://github.com/apache/spark/pull/16196
> Optimise SizeEstimator implementation
> -------------------------------------
>
> Key: SPARK-18231
> URL: https://issues.apache.org/jira/browse/SPARK-18231
> Project: Spark
> Issue Type: Improvement
> Affects Versions: 1.6.2, 2.0.1
> Reporter: Adam Roberts
>
> The SizeEstimator is used in Spark to determine whether or not we need to
> spill -- we know spilling typically has an adverse impact on performance and
> it's something we want to minimise
> We can improve the implementation of SizeEstimator in a variety of ways to
> gain a performance and increase and ultimately a reduction in footprint by
> spilling less
> There are two phases involved here
> 1) refactor to use more efficient data structures, to avoid some reflection
> calls (expensive), to remove the use of ScalaRunTime.array_apply, to use
> ThreadLocalRandom, to store an array of field offsets instead of a list of
> pointer fields and to improve the performance of the sample method
> 2) add JDK specialisms to use exact object sizes to reduce overestimations
> for both Open/Oracle JDK users and IBM Java users. With an accurate estimator
> we can therefore spill less (--footprint, ++performance -- we have observed a
> 15% reduction in RDD sizes leading to potentially double digit performance
> gains on HiBench and micro benchmarks)
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