Sean Owen created SPARK-17331:
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Summary: Avoid allocating 0-length arrays
Key: SPARK-17331
URL: https://issues.apache.org/jira/browse/SPARK-17331
Project: Spark
Issue Type: Improvement
Components: MLlib, Spark Core
Affects Versions: 2.0.0
Reporter: Sean Owen
Assignee: Sean Owen
Priority: Trivial
I've noticed a number of places in the code that allocate 0-length arrays.
Since all 0-length arrays of a type are equivalent, it's often possible to
avoid these allocations.
Where it actually likely matters is {{UTF8String}}, which does it in a several
places and which can even be replaced by {{UTF8String.EMPTY_UTF8}}, saving even
more allocations.
It _could_ be worth refactoring other occurrences, mostly of "new byte[0]", to
simply use a reference to one fixed static instance of it. But I avoided that
in the Java code on the grounds that it's a little clunky and can be added if
it proves to be a hotspot.
Same in Scala, where {{Array[T]()}} can be replaced by {{Array.empty}}. This
actually still allocates a 0-length array. However the former call actually
allocates *two* empty arrays because of varargs. The latter is simpler and
widely used in the code, so, seems worth touching up to save some garbage.
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