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From "Subramaniam Krishnan (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-3298) Add support for transitive native libraries to DistributedCache
Date Tue, 22 Apr 2008 12:48:38 GMT
Add support for transitive native libraries to DistributedCache 

                 Key: HADOOP-3298
                 URL: https://issues.apache.org/jira/browse/HADOOP-3298
             Project: Hadoop Core
          Issue Type: Improvement
          Components: mapred
         Environment: unix (different handling would be required for windows)
            Reporter: Subramaniam Krishnan
            Assignee: Arun C Murthy
             Fix For: 0.16.0

Currently if a M/R job depends on JNI based component the dynamic library must be available
in all the task nodes. This is not possible specially when you have not control on the cluster
machines, just using it as a service.

It should be possible to specify using the DistributedCache what are the native libraries
a job needs.

For example via a new method 'public void addLibrary(Path libraryPath, JobConf conf)'.

The added libraries would make it to the local FS of the task nodes (same way as cached resources)
but instead been part of the classpath they would be copied to a lib directory and that lib
directory would be added t the LD_LIBRARY_PATH of the task JVM.

An alternative would be to set the '-Djava.library.path=' task JVM parameter to the lib directory
above. However, this would break for libraries that depend on other libraries as the dependent
one would not be in the LD_LIBRARY_PATH and the OS would fail to find it as it is not the
JVM the one doing the load of the dependent one.

For uncached usage of native libraries, a special directory in the JAR could be used for native
libraries. But I'd argue that the DistributedCache enhancement would be enough, and if somebody
wants to use a native library s/he should use the DistributedCached. Or a JobConf addLibrary
method that uses the DistributedCached under the hood at submission time.

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