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POBest practice for managing different consistency levels using the Datastax Cassandra native java client
 

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  1. POBest practice for managing different consistency levels using the Datastax Cassandra native java client
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    <p>Using CQL3, the Cassandra consistency level is now set at the session level. The Datastax documentation for the native Java client states:</p> <blockquote> <p>Session instances are thread-safe and usually a single instance is all you need per application</p> </blockquote> <p>But I struggle to see how a single Session instance can handle multiple consistency levels (for example writes with QUORUM and reads with ONE). I see potential race conditions all over the place.</p> <p>An obvious solution would be to create separate sessions for reads and writes, each with the appropriate consistency level set. But this doesn't fully solve the problem. What if a class modified the consistency level for one of the two sessions? All subsequent users of the Session instance would then, unknowingly, be using the new CL.</p> <p>So, as far as I can see, the safest option is to create a new Session instance each time Cassandra needs to be accessed, with the CL explicitly set upon creation.</p> <p>What is not clear to me is whether this approach would entail a performance penalty. For example, would either <code>session = cluster.connect()</code> or <code>session.execute("CONSISTENCY [cl]")</code> involve a trip to the server?</p> <p>Am I missing something here? Has anybody got any relevant experience to share? Thanks.</p> <p>UPDATE: I see <code>com.datastax.driver.core.Query</code> has a method for setting the consistency level. So perhaps the simplest option is stick with a single Session instance and set the CL for each query.</p>
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