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From Robert Coli <rc...@digg.com>
Subject Re: Secondary indices: Why low cardinality?
Date Mon, 14 Mar 2011 00:38:56 GMT
On Thu, Mar 10, 2011 at 10:43 PM, Kevin <thebachellor@gmail.com> wrote:
>
> Can someone explain why low cardinality is advised for the secondary index?

The brief answer to your question is "because it is a local secondary index."

https://issues.apache.org/jira/browse/CASSANDRA-749

Has a pretty thorough discussion of why local secondary indexes were
chosen for the initial secondary index implementation.

https://issues.apache.org/jira/browse/CASSANDRA-749?focusedCommentId=12858175&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-12858175
" (quoting Stu Hood)
I think we agree that both approaches have their merits. The vast
difference between their best use cases needs to be considered as we
decide on a query API. In particular:

Local indexes are better for:

    * Low cardinality fields
    * Filtering of values in base order

Distributed indexes are better for:

    * High cardinality fields
    * Querying of values in index order
"

=Rob

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