I seem to recall that Impala uses snappy as the default codec for a lot of compression/decompression. May be worth upgrading to the latest release which claims a 20% improvement in decompression performance:
https://github.com/google/snappy/blob/master/NEWS (just submitted a code review to Kudu to do the same, though we use LZ4 more than snappy) -Todd -- Todd Lipcon Software Engineer, Cloudera
