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Posted to issues@impala.apache.org by "Peter Ebert (JIRA)" <ji...@apache.org> on 2019/07/12 22:09:00 UTC

[jira] [Created] (IMPALA-8759) Use double precision for HLL

Peter Ebert created IMPALA-8759:
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             Summary: Use double precision for HLL
                 Key: IMPALA-8759
                 URL: https://issues.apache.org/jira/browse/IMPALA-8759
             Project: IMPALA
          Issue Type: Improvement
            Reporter: Peter Ebert


For /be/src/exprs/aggregate-functions-ir.cc the finalize function uses a float which is only capable of 6-9 digits of precision.  More accurate estimates for larger cardinalities (beyond 999,999) should be possible with double precision.  Another c++ implementation uses double as well [https://github.com/dialtr/libcount]



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