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From "Siying Dong (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1721) use bloom filters to improve the performance of joins
Date Tue, 02 Nov 2010 19:46:26 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12927567#action_12927567
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Siying Dong commented on HIVE-1721:
-----------------------------------

So the idea is, the filtered rows in the big table fit in memory so that we can sort them
and pay sequential I/O to read the small table back? Or we do external sort for the filtered
rows from the big table?



> 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: Siying Dong
>
> 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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