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Posted to issues@beam.apache.org by "Monica Song (Jira)" <ji...@apache.org> on 2020/08/27 17:43:00 UTC

[jira] [Created] (BEAM-10824) Hash in stats.ApproximateUniqueCombineFn NON-deterministic

Monica Song created BEAM-10824:
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             Summary: Hash in stats.ApproximateUniqueCombineFn NON-deterministic
                 Key: BEAM-10824
                 URL: https://issues.apache.org/jira/browse/BEAM-10824
             Project: Beam
          Issue Type: Bug
          Components: beam-model
            Reporter: Monica Song


The python hash() function is non-deterministic. As a result, different workers will map identical values to different hashes. This leads to overestimation of the number of unique values (by several magnitudes, in my experience x1000) in a distributed processing model. 

[https://github.com/apache/beam/blob/master/sdks/python/apache_beam/transforms/stats.py#L218]

 

 



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