On Jun 24, 2014, at 4:22 PM, Andrew Wang <andrew.w...@cloudera.com> wrote:
> Since Hadoop apps can and do depend on the Hadoop classpath, the classpath > is effectively part of our API. I'm sure there are user apps out there that > will break if we make incompatible changes to the classpath. I haven't read > up on the MR JIRA Arun mentioned, but there MR isn't the only YARN app out > there. I think there is a some confusion/misunderstanding here. With hadoop-2 the user is completely in control of his own classpath (we had a similar, but limited capability in hadoop-1 w/ https://issues.apache.org/jira/browse/MAPREDUCE-1938). Furthermore, it's probably not well known that in hadoop-2 the user application (MR or otherwise) can also pick the JDK version by using JAVA_HOME env for the container. So, in effect, MR applications can continue to use java6 while YARN is running java7 - this hasn't been tested extensively though. This capability did not exist in hadoop-1. We've also made some progress with https://issues.apache.org/jira/browse/MAPREDUCE-1700 to defuse user jar-deps from MR system jars. https://issues.apache.org/jira/browse/MAPREDUCE-4421 also helps by ensuring MR applications can pick exact version of MR jars they were compiled against; and not rely on cluster installs. Hope that helps somewhat. thanks, Arun -- CONFIDENTIALITY NOTICE NOTICE: This message is intended for the use of the individual or entity to which it is addressed and may contain information that is confidential, privileged and exempt from disclosure under applicable law. If the reader of this message is not the intended recipient, you are hereby notified that any printing, copying, dissemination, distribution, disclosure or forwarding of this communication is strictly prohibited. If you have received this communication in error, please contact the sender immediately and delete it from your system. Thank You.
