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From "Alex Liu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6048) CQL3 data filtering improvement
Date Tue, 17 Sep 2013 23:42:51 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13770171#comment-13770171
] 

Alex Liu commented on CASSANDRA-6048:
-------------------------------------

Add "ALLOW FILTERING JOIN" to CQL clause. By default, it's not using join filtering, so end
user can decide when to use join filtering by specify "ALLOW JOIN FILTERING".
                
> CQL3 data filtering improvement
> -------------------------------
>
>                 Key: CASSANDRA-6048
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6048
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Alex Liu
>
> Existing data filtering uses the following algorithm
> {code}
>    1. find best selective predicate based on the smallest mean columns count
>    2. fetch rows for the best selective predicate predicate, then filter the data based
on other predicates left.
> {code}
> So potentially we could improve the performance by
> {code}
>    1.  joining multiple predicates then do the data filtering for other predicates.
>    2.  fine tune the best predicate selection algorithm
> {code}
> For multiple predicate join, it could improve performance if one predicate has many entries
and another predicate has a very few of entries. It means a few index CF read, join the row
keys, fetch rows then filter other predicates
> Another approach is to have index on multiple columns.

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