GitHub user seyfe opened a pull request:
https://github.com/apache/spark/pull/15032
[SPARK-17480][SQL] Improve perf of gatherCompressibilityStats by removing
List.length
## What changes were proposed in this pull request?
Scala's List.length method is O(N) and it makes the
gatherCompressibilityStats function O(N^2). Eliminate the List.length calls by
writing it in Scala way.
https://github.com/scala/scala/blob/2.10.x/src/library/scala/collection/LinearSeqOptimized.scala#L36
## How was this patch tested?
Profiled a Spark job and found that CompressibleColumnBuilder is using 39%
of the CPU. Out of this 39%
CompressibleColumnBuilder->gatherCompressibilityStats is using 23% of it. 6.24%
of the CPU is spend on List.length which is called inside
gatherCompressibilityStats.
After this change we started to save 6.24% of the CPU.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/seyfe/spark gatherCompressibilityStats
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/15032.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #15032
----
commit f181b92c1f3a4f91707bc1912dde29987b01c08f
Author: Ergin Seyfe <[email protected]>
Date: 2016-09-09T19:16:39Z
Improve performance of gatherCompressibilityStats by removing List.length
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