Jingsong Lee created FLINK-11964:
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Summary: Avoid hash collision of partition and bucket in
HybridHashTable
Key: FLINK-11964
URL: https://issues.apache.org/jira/browse/FLINK-11964
Project: Flink
Issue Type: Improvement
Components: Runtime / Operators
Reporter: Jingsong Lee
In HybridHashTable, first select the corresponding partition according to
hashCode, and then select the bucket in the partition according to hashCode, so
using the same hashCode can easily cause hash collision.
Consider doing some mix to hashCode when choosing bucket.
We can just XOR some shifted bits in the cheapest possible way to reduce
systematic lossage, as well as to incorporate impact of the highest bits that
would otherwise never be used in index calculations because of table bounds.
(bucket use power-of-two masking). Just like: (hash ^ (hash >>> 16))
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