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From "Joydeep Sen Sarma (JIRA)" <>
Subject [jira] Commented: (HIVE-1721) use bloom filters to improve the performance of joins
Date Tue, 02 Nov 2010 19:20:26 GMT


Joydeep Sen Sarma commented on HIVE-1721:

@Siyin - that's a good question. I don't know statistically how common it is - but we have
heard requests along these lines. for example one use case is that one project wants to get
some data for a reasonably large subset of the users. one use case we have seen was where
0.2% of users were interesting - but even 0.2% is very large for us. people also use semi-joins
and that pretty much says that people want to filter rows out.

> use bloom filters to improve the performance of joins
> -----------------------------------------------------
>                 Key: HIVE-1721
>                 URL:
>             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
> 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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