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Date: Wed, 5 Sep 2012 22:32:19 -0700
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Subject: Secondary index read/write explanation
From: Venkat Rama <venkata.s.rama@gmail.com>
To: user@cassandra.apache.org
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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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Hi All,<div><br></div><div>I am a new bee to Cassandra and trying to unders=
tand how secondary indexes work. =A0I have been going over the discussion o=
n=A0<a href=3D"https://issues.apache.org/jira/browse/CASSANDRA-749">https:/=
/issues.apache.org/jira/browse/CASSANDRA-749</a> about local secondary inde=
xes. And interesting question on=A0<a href=3D"http://www.mail-archive.com/u=
ser@cassandra.apache.org/msg16966.html">http://www.mail-archive.com/user@ca=
ssandra.apache.org/msg16966.html</a>. =A0The discussion seems to assume tha=
t most common uses cases are ones with range queries. =A0Is this right?=A0<=
/div>
<div><br></div><div>I am trying to understand the low cardinality reasoning=
 and how the read gets executed. =A0I have following questions, hoping i ca=
n explain my question well :)</div><div><br></div><div>1. =A0When a write r=
equest is received, it is written to the base CF and secondary index to sec=
ondary (hidden) CF. If this right, will the secondary index be written loca=
l the node or will it follow RP/OPP to write to nodes.</div>
<div>2. =A0When a coordinator receives a read request with say predicate x=
=3Dy 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 locall=
y indexed?</div>
<div><br></div><div>If there is any article/blog that can help understand t=
his better, please let me know.</div><div><br></div><div>Thanks again in ad=
vance.</div><div><br></div><div>VR</div><div><br></div>

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