Cassandra / Hadoop : Getting the row key (when iterating over all rows)

I thought I would save some people some time...

The word count example is fantastic, and is enough to get you going. But, you it may leave you wondering how to get at the row key since the "key" passed into the map is the name of the column and not the key of the row. Instead the key is in the context. Take a look at the snippet below.

public void map(ByteBuffer key, SortedMap<ByteBuffer, IColumn> columns, Context context) 
   throws IOException, InterruptedException {
  for (ByteBuffer columnKey : columns.keySet()){
     String name = ByteBufferUtil.string(columns.get(columnKey).name());
     String value = ByteBufferUtil.string(columns.get(columnKey).value());            
     logger.info("[" + ByteBufferUtil.string(columnKey) + "]->[" + name + "]:[" + value + "]");
      logger.info("Context [" + ByteBufferUtil.string(context.getCurrentKey()) + "]);             
  }

}

Cassandra / Hadoop : No local connection available

If you are trying to run the word_count example in Cassandra Hadoop, and you encounter the following exception:

java.lang.RuntimeException: java.lang.UnsupportedOperationException: no local connection available
at org.apache.cassandra.hadoop.ColumnFamilyRecordReader.initialize(ColumnFamilyRecordReader.java:132)
at org.apache.hadoop.mapred.MapTask$NewTrackingRecordReader.initialize(MapTask.java:418)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:620)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:305)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:177)
Caused by: java.lang.UnsupportedOperationException: no local connection available
at org.apache.cassandra.hadoop.ColumnFamilyRecordReader.getLocation(ColumnFamilyRecordReader.java:176)
at org.apache.cassandra.hadoop.ColumnFamilyRecordReader.initialize(ColumnFamilyRecordReader.java:113)
... 4 more

Then you have hit a problem with local IP resolution in Java.

Cassandra currently uses the following line to resolve IP addresses;

localAddresses = InetAddress.getAllByName(InetAddress.getLocalHost().getHostAddress());

There are better ways to do this using the NetworkInterface,

http://stackoverflow.com/questions/901755/how-to-get-the-ip-of-the-computer-on-linux-through-java

http://www.jguru.com/faq/view.jsp?EID=790132

But until Cassandra uses that you'll need to make sure that the bit of code above resolves properly by manipulating your /etc/hosts to resolve localhost to match the configuration in Cassandra, which by default is looking for localhost bound to 127.0.0.1.

I submitted a patch for this. If you are having issues, please vote to get the patch accepted.
https://issues.apache.org/jira/browse/CASSANDRA-3211