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Posted to issues@beam.apache.org by "Monica Song (Jira)" <ji...@apache.org> on 2020/09/02 04:55:00 UTC

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

     [ https://issues.apache.org/jira/browse/BEAM-10824?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Monica Song updated BEAM-10824:
-------------------------------
    Component/s:     (was: beam-model)
                 sdk-py-core

> Hash in stats.ApproximateUniqueCombineFn NON-deterministic
> ----------------------------------------------------------
>
>                 Key: BEAM-10824
>                 URL: https://issues.apache.org/jira/browse/BEAM-10824
>             Project: Beam
>          Issue Type: Bug
>          Components: sdk-py-core
>            Reporter: Monica Song
>            Priority: P1
>              Labels: hash
>   Original Estimate: 24h
>          Time Spent: 1h 50m
>  Remaining Estimate: 22h 10m
>
> 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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