public boolean nextBlock() throws IOException {
      int keyLength = nextKeyBuffer();
      if(keyLength > 0) {
        currentValueBuffer();
        return true;
      }
      return false;
    }
Read and return the next record length, potentially skipping over a sync
block.

@return the length of the next record or -1 if there is no next record
@throws IOException
ql/src/java/org/apache/hadoop/hive/ql/io/RCFile.java