@Override
      public Object call() throws Exception {
        if (null == regionName) {
          return getTotalPreCompressedBytes();
        } else {
          return getTotalPreCompressedBytes(regionName);
        }
      }
Returns the number of pre-compressed bytes stat on a virtual machine.

@param vm a virtual machine.
@param regionName a region. Indicates whole cache if null.
geode-core/src/distributedTest/java/org/apache/geode/internal/compression/CompressionStatsDUnitTest.java