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From Simon Smith <simongsm...@gmail.com>
Subject Re: What happened if one server involved in the process of data reading fail?
Date Thu, 20 May 2010 13:08:34 GMT
On Thu, May 20, 2010 at 8:08 AM, 史英杰 <shiyingjie1983@gmail.com> wrote:
> Hi, All,
>     I am now learning the mechanism Cassandra adopts to get high
> availability and fault tolerance.  As I know, we should connect to one
> server of Cassandra first, then we can read or write data  through it, so if
> the server which we connect to get down, what will happen? Should we have to
> reconnect another server or will Cassandra control this situation?


The approach we're taking is to put the software load-balancer haproxy
in front of our cassandra cluster.  Use "mode tcp" within haproxy's
config.  I notice that Tragedy (http://github.com/enki/tragedy/) also
lets you put a list of servers into the connection call (we're going
to put the list of haproxy load balancers here).



> Another sutiation, if the server which is involved in the process of data reading
> fail, what will Cassandra do?


If you're using Thrift to connect, catch the exceptions that library
throws if unable to connect and then try to connect again.   This is
going to happen - if/when a node goes down it causes the entire
cluster to hiccup a little, so if it is critical that any particular
read transaction succeeds, you may need to sleep as much as 5 seconds
(this is just my experience).


>     Thanks a lot!
>
> Yingjie

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