Extracting bzipped tarballs is very slow
Jobsub's tar file feature now uses bzip2 encoding. I noticed that extracting the tar files was taking a lot of cpu time on the test cvmfs publishing, and heard that uncompressing bzip2 was about 5 times slower than gzip. Dennis helped me to do a test by creating an approximately 1GB gzipped tar file with exactly the same contents as a formerly used bzip2 tar file, and found that it was 8.5 times faster: it took only 16 seconds to extract instead of 137 seconds. So I suggest switching to use gzip.
Dennis had originally used bzip2 because with gzip the hash changes each time, but the gzip -n option avoids that.
The cvmfs publishing itself is not a very high priority since that is just a test at this point, but this should also save significant time in decompression of these tar files on worker nodes.