I would check out http://wiki.apache.org/cassandra/HadoopSupport for more info. I'll try to explain a bit more here, but I don't think there's a tutorial out there yet.
For input: - configure your main class where you're starting the mapreduce job the way the word_count is configured (with either storage-conf or in your code via the ConfigHelper). It will complain specifically about stuff you hadn't configured - esp. important is your cassandra server and port. - the inputs to your mapper are going to be what's coming from cassandra - so your key with a map of row values - you need to set your column name in your overridden setup method in your mapper - for the reducer, nothing really changes from a normal map/reduce, unless you want to output to cassandra - generally cassandra just provides an inputformat and split classes to read from cassandra - you can find the guts in the org.apache.cassandra.hadoop package For output: - in your reducer, you could just write to cassandra directly via thrift. there is a built-in outputformat coming in 0.7 but it still might change before 0.7 final - that will queue up changes so it will write large blocks all at once. On Aug 19, 2010, at 12:07 PM, Mark wrote: > Are there any examples/tutorials on the web for reading/writing from > Cassandra into/from Hadoop? > > I found the example in contrib/word_count but I really can't make sense of > it... a tutorial/explanation would help.
