Autocomplete server-side implementation

Question

What is a fast and efficient way to implement the server-side component for an autocomplete feature in an html input box?

I am writing a service to autocomplete use

Answer 1

I ended up resolving this one via Lucene; the initial performance tests seem sufficient for our use case. A little hacking was necessary to make the prefix queries work, as I was running into the TooManyClauses exception when expanding queries such as "Jeff At*". I ended up wrapping my IndexReader with a FilterIndexReader, and set hard cap on the number of terms returned on a prefix term call. Here's my code:

Directory directory = FSDirectory.getDirectory(indexDir);
IndexReader reader = IndexReader.open(directory);
FilterIndexReader filteredReader = new FilterIndexReader(reader) {
  @Override public TermEnum terms(Term t) throws IOException {
    final TermEnum origEnum = super.terms(t);

    return new TermEnum() {
      protected int count = 0;
      @Override public boolean next() throws IOException {
        if (count++ < (BooleanQuery.getMaxClauseCount() - 10))
          return origEnum.next();
        else return false;
      }

      @Override public Term term() {
        return origEnum.term();
      }

      @Override public int docFreq() {
        return origEnum.docFreq();
      }

      @Override public void close() throws IOException {
        origEnum.close();
      }
    };
  }
};

IndexSearcher searcher = new IndexSearcher(filteredReader);