To efficiently run map reduce on the data that has been HAR'ed it will be great to actually implement getFileBlockLocations for a given filename.
This way the JobTracker will have information about data locality and will schedule tasks appropriately.
I believe the overhead introduced by doing lookups in the index files can be smaller than that of copying data over the wire.
Will upload the patch shortly, but would love to get some feedback on this. And any ideas on how to test it are very welcome.