code: private void writeObject(ObjectOutputStream out) throws IOException {
  		out.writeInt(batchSize);
  		this.conf.write(out);
  		out.writeUTF(schema.toString());
  
  		out.writeInt(selectedFields.length);
  		for (int f : selectedFields) {
  			out.writeInt(f);
  		}
  
  		out.writeInt(conjunctPredicates.size());
  		for (Predicate p : conjunctPredicates) {
  			out.writeObject(p);
  		}
  	}
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