Anton Okolnychyi created SPARK-26205:
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Summary: Optimize In expression for bytes, shorts, ints
Key: SPARK-26205
URL: https://issues.apache.org/jira/browse/SPARK-26205
Project: Spark
Issue Type: Improvement
Components: SQL
Affects Versions: 3.0.0
Reporter: Anton Okolnychyi
Currently, {{In}} expressions are compiled into a sequence of if-else
statements, which results in O\(n\) time complexity. {{InSet}} is an optimized
version of {{In}}, which is supposed to improve the performance if the number
of elements is big enough. However, {{InSet}} actually degrades the performance
in many cases due to various reasons (benchmarks will be available in
SPARK-26203 and solutions are discussed in SPARK-26204).
The main idea of this JIRA is to make use of {{tableswitch}} and
{{lookupswitch}} bytecode instructions. In short, we can improve our time
complexity from O\(n\) to O\(1\) or at least O\(log n\) by using Java
{{switch}} statements. We will have O\(1\) time complexity if our case values
are compact and {{tableswitch}} can be used. Otherwise, {{lookupswitch}} will
give us O\(log n\).
An important benefit of the proposed approach is that we do not have to pay an
extra cost for autoboxing as in case of {{InSet}}. As a consequence, we can
substantially outperform {{InSet}} even on 250+ elements.
See
[here|https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-3.html#jvms-3.10]
and here for
[more|https://stackoverflow.com/questions/10287700/difference-between-jvms-lookupswitch-and-tableswitch]
information.
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