intermediate results not getting compressed

[Billy Pearson]

I am running a large streaming job that processes that about 3TB of data I 
am seeing large jumps in hard drive space usage in the reduce part of the 
jobs I tracked the problem down. The job is set to compress map outputs but 
looking at the intermediate files on the local drives the intermediate files 
are not getting compressed during/after merges. I am going from having say 
2Gb of mapfile.out files to having one intermediate.X file sizing 100-350% 
larger then the map files. I have looked at one of the files and confirmed 
that it is not getting compressed as I can read the data in it. if it was 
only one merge then it would not be a problem but when you are merging 
70-100 of these you use tons of GB's and my task are starting to die as they 
run out of hard drive space end the end kill the job.

I am running 0.19.1-dev, r744282. I have searched the issues but found 
nothing about the compression.
Should the intermediate results not be compressed also if the map output 
files are set to be compressed?
If not then why do we have the map compression option just to save network 
traffic?