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From "Edward Capriolo (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-7121) Use murmur hash to distribute HiveKey
Date Sun, 25 May 2014 16:59:01 GMT

    [ https://issues.apache.org/jira/browse/HIVE-7121?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14008377#comment-14008377
] 

Edward Capriolo commented on HIVE-7121:
---------------------------------------

Does this effect bucketed tables? I think it does and then we can not just change the hash
code because that would break assumptions of what is in the bucket. IE i create a bucket in
hive 12, and in hive 13 different data would be in the bucket.

I think this is why:

org.apache.hadoop.hive.cli.TestMinimrCliDriver.testCliDriver_infer_bucket_sort_num_buckets
org.apache.hadoop.hive.cli.TestMinimrCliDriver.testCliDriver_quotedid_smb

These tests are failing. If this is the case we need a way or recording the hashcode in the
metadata for the table.

> Use murmur hash to distribute HiveKey
> -------------------------------------
>
>                 Key: HIVE-7121
>                 URL: https://issues.apache.org/jira/browse/HIVE-7121
>             Project: Hive
>          Issue Type: Bug
>          Components: Query Processor
>            Reporter: Gopal V
>            Assignee: Gopal V
>         Attachments: HIVE-7121.1.patch, HIVE-7121.WIP.patch
>
>
> The current hashCode implementation produces poor parallelism when dealing with single
integers or doubles.
> And for partitioned inserts into a 1 bucket table, there is a significant hotspot on
Reducer #31.
> Removing the magic number 31 and using a more normal hash algorithm would help fix these
hotspots.



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