[jira] [Commented] (HIVE-1721) use bloom filters to improve the performance of joins

["Ashutosh Chauhan (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-1721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13267637#comment-13267637 ] 

Ashutosh Chauhan commented on HIVE-1721:
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@Alex,
No jira was created after map-join. I think goal of this jira is to improve performance of joins in case one of the table is big enough that it cant be read in each mapper's memory, but may be amenable to other performance tricks.
                
> 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
>              Labels: gsoc, gsoc2012, 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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