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From "Ning Zhang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-562) join does not work well if there is a very large skew in keys
Date Wed, 21 Oct 2009 20:58:59 GMT

    [ https://issues.apache.org/jira/browse/HIVE-562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12768449#action_12768449
] 

Ning Zhang commented on HIVE-562:
---------------------------------

Can this be done by storing input (storage in JoinOperator.java and CommonJoinOperator.java)
from one group to an external-storage-backed hash table (eg., HTree in JDBM as map-side join)
rather than main memory hash table?

> join does not work well if there is a very large skew in keys
> -------------------------------------------------------------
>
>                 Key: HIVE-562
>                 URL: https://issues.apache.org/jira/browse/HIVE-562
>             Project: Hadoop Hive
>          Issue Type: Improvement
>          Components: Query Processor
>    Affects Versions: 0.4.0
>            Reporter: Namit Jain
>
> Only the last table is streamed in case of regular joins.
> So, for any other table, or for any small table (in case of map-joins), if the number
of values for a given key are very large, it does not scale.

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