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From Venkat Rama <venkata.s.r...@gmail.com>
Subject Secondary index read/write explanation
Date Thu, 06 Sep 2012 05:32:19 GMT
Hi All,

I am a new bee to Cassandra and trying to understand how secondary indexes
work.  I have been going over the discussion on
https://issues.apache.org/jira/browse/CASSANDRA-749 about local secondary
indexes. And interesting question on
http://www.mail-archive.com/user@cassandra.apache.org/msg16966.html.  The
discussion seems to assume that most common uses cases are ones with range
queries.  Is this right?

I am trying to understand the low cardinality reasoning and how the read
gets executed.  I have following questions, hoping i can explain my
question well :)

1.  When a write request is received, it is written to the base CF and
secondary index to secondary (hidden) CF. If this right, will the secondary
index be written local the node or will it follow RP/OPP to write to nodes.
2.  When a coordinator receives a read request with say predicate x=y where
column x is the secondary index, how does the coordinator query relevant
node(s)? How does it avoid sending it to all nodes if it is locally indexed?

If there is any article/blog that can help understand this better, please
let me know.

Thanks again in advance.

VR

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