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From "J. Andrew Key (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-1721) use bloom filters to improve the performance of joins
Date Thu, 07 Jul 2011 05:27:16 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13061038#comment-13061038
] 

J. Andrew Key commented on HIVE-1721:
-------------------------------------

I may use org.apache.hadoop.util.bloom.BloomFilter http://svn.apache.org/repos/asf/hadoop/common/trunk/common/src/java/org/apache/hadoop/util/bloom/BloomFilter.java.
 
Should there be a query syntax for controlling the creation of the bloom filter with options
such as:
1. vector size, hash function type and number?
2. expected table size and acceptable level of false positives?

If anyone has any preference or ideas, please share them.



> use bloom filters to improve the performance of joins
> -----------------------------------------------------
>
>                 Key: HIVE-1721
>                 URL: https://issues.apache.org/jira/browse/HIVE-1721
>             Project: Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: J. Andrew Key
>              Labels: optimization
>
> In case of map-joins, it is likely that the big table will not find many matching rows
from the small table.
> Currently, we perform a hash-map lookup for every row in the big table, which can be
pretty expensive.
> It might be useful to try out a bloom-filter containing all the elements in the small
table.
> Each element from the big table is first searched in the bloom filter, and only in case
of a positive match,
> the small table hash table is explored.

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