Using Hadoop 2.2 as a sink in Flume 1.4

Google really screwed the pooch with their protobuf 2.5 release. Code generated with protobuf 2.5 is binary incompatible with older protobuf libraries (I guess Google missed the semantic versioning boat on this release). Unfortunately the current stable release of Flume 1.4 packages protobuf 2.4.1 and if you try and use HDFS on Hadoop 2.2 as a sink you’ll be smacked with the following exception:

java.lang.VerifyError: class org.apache.hadoop.security.proto.SecurityProtos$GetDelegationTokenRequestProto
overrides final method getUnknownFields.()Lcom/google/protobuf/UnknownFieldSet;
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
    at org.apache.hadoop.ipc.ProtobufRpcEngine.getProxy(ProtobufRpcEngine.java:92)
    at org.apache.hadoop.ipc.RPC.getProtocolProxy(RPC.java:537)
    at org.apache.hadoop.hdfs.NameNodeProxies.createNNProxyWithClientProtocol(NameNodeProxies.java:328)
    at org.apache.hadoop.hdfs.NameNodeProxies.createNonHAProxy(NameNodeProxies.java:235)

Hadoop 2.2 uses protobuf 2.5 for its RPC, and Flume loads its older packaged version of protobuf ahead of Hadoop’s, which causes this error. To fix this you’ll need to move both protobuf and guava out of Flume’s lib directory. The following command moves them into your home directory.

$ mv ${flume_bin}/lib/{protobuf-java-2.4.1.jar,guava-10.0.1.jar} ~/

Now if you restart your Flume agent you’ll be able to target HDFS as a sink with Hadoop 2.2. Great success!

Flume’s next release will move to protobuf 2.5 so this problem should magically disappear in due course.

About the author

Hadoop in Practice, Second Edition

Alex Holmes works on tough big-data problems. He is a software engineer, author, speaker, and blogger specializing in large-scale Hadoop projects. He is the author of Hadoop in Practice, a book published by Manning Publications. He has presented multiple times at JavaOne, and is a JavaOne Rock Star.

If you want to see what Alex is up to you can check out his work on GitHub, or follow him on Twitter or Google+.

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