[jira] [Created] (KYLIN-1379) More stable precise count distinct implements after KYLIN-1186

["Yerui Sun (JIRA)" <ji...@apache.org>]

Yerui Sun created KYLIN-1379:
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             Summary: More stable precise count distinct implements after KYLIN-1186
                 Key: KYLIN-1379
                 URL: https://issues.apache.org/jira/browse/KYLIN-1379
             Project: Kylin
          Issue Type: Improvement
          Components: Job Engine
    Affects Versions: v2.1, v1.3
            Reporter: Yerui Sun
            Assignee: Yerui Sun


After KYLIN-1186, we've gained the ability to count distinct int type columns.
However, the implements of KYLIN-1186 is not stable, especially in 2.x-staging branch.
The reason is that the measure's maxlength is used to allocate memory in 2.x version, and the BitmapMeasure is hardcoded to 8MB in KYLIN-1186, causing OOM when cube building.
To resolve this problem, we have introduce precision on the bitmap measure, such as bitmap(100), bitmap(10000), bitmap(1000000), meaning the measure could accept 100/10000/1M cardinality at most. This solution should be fine, considering the reality, if the count value over 1000000, the hyperloglog measure which produce approx. result should be acceptable.



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