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From "Zoltan Haindrich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-19501) Fix HyperLogLog to be threadsafe
Date Mon, 14 May 2018 12:04:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-19501?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16474085#comment-16474085
] 

Zoltan Haindrich commented on HIVE-19501:
-----------------------------------------

I think adding sync-s would probably slow things even more down; Gopal's wip patch in HIVE-18866
also removes these fields

> 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
>            Assignee: Laszlo Bodor
>            Priority: Major
>         Attachments: HIVE-19501.01.patch
>
>
> 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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