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https://issues.apache.org/jira/browse/FLINK-11964?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jingsong Lee updated FLINK-11964:
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Summary: Avoid hash collision of partition and bucket in HybridHashTable in
Blink SQL (was: Avoid hash collision of partition and bucket in
HybridHashTable)
> Avoid hash collision of partition and bucket in HybridHashTable in Blink SQL
> ----------------------------------------------------------------------------
>
> Key: FLINK-11964
> URL: https://issues.apache.org/jira/browse/FLINK-11964
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / Operators
> Reporter: Jingsong Lee
> Priority: Major
>
> In HybridHashTable, first select the corresponding partition according to
> hashCode, and then select the bucket in the partition according to hashCode,
> using the same hashCode can easily cause hash collision.
> Consider doing some mix to hashCode when choosing bucket.
> Like JDK HashMap, 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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