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From "Brock Noland (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-8707) Fix ordering differences due to Java 8 HashMap function
Date Sun, 16 Nov 2014 01:38:34 GMT

    [ https://issues.apache.org/jira/browse/HIVE-8707?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14213830#comment-14213830
] 

Brock Noland commented on HIVE-8707:
------------------------------------

Thank you Mohit! The change looks great. I am wondering should we do something to document
that these maps should be a deterministic ordered map? For example we could add a javadoc
to their declaration, create a tiny wrapper {{LinkedHashMap}} say called {{DeterminsiticOrderedMap}}
or just put a comment where we create the Map saying must be deterministic referencing this
jIRA?

> Fix ordering differences due to Java 8 HashMap function
> -------------------------------------------------------
>
>                 Key: HIVE-8707
>                 URL: https://issues.apache.org/jira/browse/HIVE-8707
>             Project: Hive
>          Issue Type: Sub-task
>            Reporter: Mohit Sabharwal
>            Assignee: Mohit Sabharwal
>         Attachments: HIVE-8707.1.patch, HIVE-8707.patch
>
>
> Java 8 uses a different hash function for HashMap, which is leading to iteration order
differences in several cases. (See [Java8|http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/8-b132/java/util/HashMap.java?av=f#336]
vs [Java7|http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/7-b147/java/util/HashMap.java#HashMap.hash%28int%29])
> For example:
>   - In Explain output: Stages are numbered differently  
>   - In PostExecutePrinter hook, table order is different in lineage.



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