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Posted to dev@calcite.apache.org by "Haisheng Yuan (Jira)" <ji...@apache.org> on 2020/06/30 04:06:00 UTC

[jira] [Created] (CALCITE-4096) Change Pair.hashCode() not to use XOR

Haisheng Yuan created CALCITE-4096:
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             Summary: Change Pair.hashCode() not to use XOR
                 Key: CALCITE-4096
                 URL: https://issues.apache.org/jira/browse/CALCITE-4096
             Project: Calcite
          Issue Type: Improvement
          Components: core
            Reporter: Haisheng Yuan


JDK Map Entry uses XOR maybe because it is unlikely to use Map Entry as the HashMap key.

But Pair in Calcite is a general data structure, it is used in several places as the key of HashMap/HashSet. XOR is not a good candidate for hash algorithm, it is more likely to generate hash collision than simple prime multiplication, especially when pair.left equals pair.right.



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