@Override
    public String toString() {
      StringBuilder buf = new StringBuilder();
      buf.append(size());
      buf.append(':');
      if (size() > 0) {
        for (Path p : this) {
          String pStr = p.toString();
          buf.append(pStr.length());
          buf.append(':');
          buf.append(pStr);
        }
      }
      return buf.toString();
    }
This input format returns its own input split as a value.  This is because our splits
contain information needed to properly construct the writer.  Crazy, huh?
ql/src/java/org/apache/hadoop/hive/ql/txn/compactor/MRCompactor.java