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[jira] [Created] (HIVE-19501) Fix HyperLogLog to be threadsafe


Zoltan Haindrich created HIVE-19501:
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             Summary: Fix HyperLogLog to be threadsafe
                 Key: HIVE-19501
                 URL: https://issues.apache.org/jira/browse/HIVE-19501
             Project: Hive
          Issue Type: Bug
            Reporter: Zoltan Haindrich


not sure if this is an issue in reality or not; but there are 3 static fields in HyperLogLog which are rewritten during working; if there are multiple threads are calculating HLL in the same JVM, there is a theoretical chance that they might overwrite eachothers value...

static fields:
https://github.com/apache/hive/blob/8028ce8a4cf5a03e2998c33e032a511fae770b47/standalone-metastore/src/main/java/org/apache/hadoop/hive/common/ndv/hll/HyperLogLog.java#L65

usage:
https://github.com/apache/hive/blob/8028ce8a4cf5a03e2998c33e032a511fae770b47/standalone-metastore/src/main/java/org/apache/hadoop/hive/common/ndv/hll/HyperLogLog.java#L216



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