@Override
 public ChunkCacheKey readObject(ObjectInput input) throws IOException {
   String indexName = input.readUTF();
   String fileName = input.readUTF();
   int chunkId = UnsignedNumeric.readUnsignedInt(input);
   return new ChunkCacheKey(indexName, fileName, chunkId);
 }
 @Override
 public void writeObject(ObjectOutput output, ChunkCacheKey key) throws IOException {
   output.writeUTF(key.indexName);
   output.writeUTF(key.fileName);
   UnsignedNumeric.writeUnsignedInt(output, key.chunkId);
 }