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From "Alex Liu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6048) Add the ability to use multiple indexes in a single query
Date Mon, 21 Oct 2013 18:47:43 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13800948#comment-13800948
] 

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

http://remis-thoughts.blogspot.com/2012/03/perfect-hashes-in-java-given-set-of-m.html provides
a perfect hash for a set. We can select the primary index and secondary index combination
set to create a perfect hash. 

Usage is here.
http://code.google.com/p/perfect-hashes/source/browse/trunk/src/test/java/com/googlecode/perfecthashes/PerfectHashesTest.java?r=33

> Add the ability to use multiple indexes in a single query
> ---------------------------------------------------------
>
>                 Key: CASSANDRA-6048
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6048
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Alex Liu
>            Assignee: Alex Liu
>             Fix For: 2.1
>
>         Attachments: 6048-1.2-branch.txt, 6048-trunk.txt
>
>
> 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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