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https://issues.apache.org/jira/browse/HIVE-2845?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13235371#comment-13235371
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Namit Jain commented on HIVE-2845:
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This may not be very useful in the current hive setup, since the point lookup
on the hive index is not very fast.
However, this opens up a very wide variety of applications.
Consider the scenario when one of the tables is stored in HBase. In that case,
a join with other table can be reduced
to a map-only job, with the mapper doing a point lookup for every row. This is
very different from map-join where one of
the tables is so small that it fits in memory.
> Add support for index joins in Hive
> -----------------------------------
>
> Key: HIVE-2845
> URL: https://issues.apache.org/jira/browse/HIVE-2845
> Project: Hive
> Issue Type: New Feature
> Reporter: Namit Jain
> Labels: gsoc, gsoc2012
>
> Hive supports indexes, which are used for filters currently.
> It would be very useful to add support for index-based joins in Hive.
> If 2 tables A and B are being joined, and an index exists on the join key of
> A,
> B can be scanned (by the mappers), and for each row in B, a lookup for the
> corresponding row in A can be performed.
> This can be very useful for some usecases.
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