When using the -libjars option to add classes to the classpath, every library so added is explicitly listed in the ContainerLaunchContext's local resources even though they're all uploaded to the same directory in HDFS. When using tools like Crunch without an uber JAR or when trying to take advantage of the shared cache, the number of libraries can be quite large. We've seen many cases where we had to turn down the max number of applications to prevent ZK from running out of heap because of the size of the state store entries.
Rather than listing all files independently, this JIRA proposes to have the NM allow wildcards in the resource localization paths. Specifically, we propose to allow a path to have a final component (name) set to "*", which is interpreted by the NM as "download the full directory and link to every file in it from the job's working directory." This behavior is the same as the current behavior when using -libjars, but avoids explicitly listing every file.
This JIRA does not attempt to provide more general purpose wildcards, such as "*.jar" or "file*", as having multiple entries for a single directory presents numerous logistical issues.
This JIRA also does not attempt to integrate with the shared cache. That work will be left to a future JIRA. Specifically, this JIRA only applies when a full directory is uploaded. Currently the shared cache does not handle directory uploads.
This JIRA proposes to allow for wildcards both in the internal processing of the -libjars switch and in paths added through the Job and DistributedCache classes.
The proposed approach is to treat a path, "dir/*", as "dir" for purposes of all file verification and localization. In the final step, the NM will query the localized directory to get a list of the files in "dir" such that each can be linked from the job's working directory. Since $PWD/* is always included on the classpath, all JAR files in "dir" will be in the classpath.