Hello Pradeep,
Let me try to help you, I faced a similar issue, too.
Thing is I was told selecting all the records at once is not an ideal approach.
No matter how strong the hardware is an arbitrary upward adjusted RPC time out would not help, whatever value you give to it, the ‘SELECT *’ query would die.
I ended up creating a program that implements paging, I had my CQL LIMIT <value> set to a relatively reasonable [small] number and was able to suck ~500K reocrds out.
Sent: Wednesday, September 18, 2013 9:05 AM
Subject: Re: RPC timeout error while exporting data from CQL
Experts.. Any help?

On Wed, Sep 18, 2013 at 2:55 PM, pradeep kumar <pradeepkumardv@gmail.com> wrote:
Hello all,
I am trying to export data from cassandra using CQL client. A column family has about 100000 rows in it. when i am copying dta into csv file using COPY TO command i get following rpc_time out error.
copy mycolfamily to '/root/mycolfamily.csv'
Request did not complete within rpc_timeout.
I am running in [cqlsh 3.1.6 | Cassandra 1.2.8 | CQL spec 3.0.0 | Thrift protocol 19.36.0]
how can i increase rpc timeout limit?
I tried adding rpc_timeout_in_ms: 20000 (defalut is 10000) in my conf/cassandra.yaml file. but while restarting cassandra i get
[root@user ~]# null; Can't construct a java object for tag:yaml.org,2002:org.apache.cassandra.config.Config; exception=Cannot create property=rpc_timeout_in_ms for JavaBean=org.apache.cassandra.config.Config@71bfc4fc; Unable to find property 'rpc_timeout_in_ms' on class: org.apache.cassandra.config.Config
Invalid yaml; unable to start server.  See log for stacktrace.
please help me.
Thanks in advance.