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POMaking a Cassandra Connection inside Hadoop MapReduce Task
 

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  1. POMaking a Cassandra Connection inside Hadoop MapReduce Task
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    <p>I am successfully using the <a href="https://github.com/datastax/java-driver" rel="nofollow">DataStax Java Driver</a> to access Cassandra inside my Java code just before I start a MapReduce Job. </p> <pre class="lang-java prettyprint-override"><code> cluster = Cluster.builder().addContactPoint("127.0.0.1").build(); </code></pre> <p>However I am needing to check additional information to decide on a per record basis how to reduce the record. If I attempt to use the same code inside a Hadoop Reducer class it fails to connect with the error:</p> <pre><code>INFO mapred.JobClient: Task Id : attempt_201310280851_0012_r_000000_1, Status : FAILED com.datastax.driver.core.exceptions.NoHostAvailableException: All host(s) tried for query failed (tried: /127.0.0.1 ([/127.0.0.1] Unexpected error during transport initialization (com.datastax.driver.core.TransportException: [/127.0.0.1] Error writing))) at com.datastax.driver.core.ControlConnection.reconnectInternal(ControlConnection.java:186) at com.datastax.driver.core.ControlConnection.connect(ControlConnection.java:81) at com.datastax.driver.core.Cluster$Manager.init(Cluster.java:662) at com.datastax.driver.core.Cluster$Manager.access$100(Cluster.java:604) at com.datastax.driver.core.Cluster.&lt;init&gt;(Cluster.java:69) at com.datastax.driver.core.Cluster.buildFrom(Cluster.java:96) at com.datastax.driver.core.Cluster$Builder.build(Cluster.java:585) </code></pre> <p>The MapReduce input and output will successfully read and write to Cassandra. As I mentioned I can connect before I run the job so I do not think it is an issue with the Cassandra server.</p>
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    1. USJohn
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      1. POMaking a Cassandra Connection inside Hadoop MapReduce Task
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    1. COAny other errors? Is this a complete exception? Any errors on the server side?
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      1. POMaking a Cassandra Connection inside Hadoop MapReduce Task
      1. USPiotr Kołaczkowski
    2. CONo that was the only error, it did not happen when the job tracker was set to local. That said I have moved to using PIG instead now.
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      1. POMaking a Cassandra Connection inside Hadoop MapReduce Task
      1. USJohn
    3. COIs it a single node cluster? If it has more nodes, then your reducer might be run on some other node. Are you sure you can connect to localhost from *all* of the nodes?
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      1. POMaking a Cassandra Connection inside Hadoop MapReduce Task
      1. USPiotr Kołaczkowski
 

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