java - Lucene Search with MultiThreads -

i need execute in machine learning project >3000 queries in index 3gb size.

in order speed performance create 4 threads(i got 4 cores in macbook pro) , gave each 1 part of total queries(if got n queries in total each thread got n/4 queries).

i open index via fsdirectory.open(file) , share indexsearcher threads.

the problem don't see performance improvement neither cpu increase. played different number of threads still no change.

to save whole index in ram not possible!

i saw on other threads solution open index read use lucene 4.3 write options removed reader no worries read mode anymore!

i aware this page , tips give looks quiet out of date.

so question how can parallel index search in order improve performance real lucene?

below example code using:

list<string> querylist = new arraylist<string>(); list<thread> threads = new arraylist<thread>(); for(int i=0;i<number_threads;i++){           list<string> querysublist = querylist.sublist(fromindex, toindex);                   queryparser ngramindexqueryparser = new queryparser(version.lucene_43, "ngram", new keywordanalyzer());         startworker(querysublist, threads, date, ngramindexqueryparser, ngramsearcher); }   public static void startworker(list<string> querysublist,  list<thread> threads,queryparser ngramindexqueryparser,indexsearcher ngramsearcher){     ngramindexsearch task = new ngramindexsearch(querylist, ngramindexqueryparser, ngramsearcher);     thread worker = new thread(task);     worker.start();     threads.add(worker); }   public class ngramindexsearch implements runnable {     public ngramindexsearch(list<string> querylist, string year,queryparser queryparser, indexsearcher searcher){ //initialization     }     public void run() {       for(string q:querylist){             query query = queryparser.parse(querytext);             topdocs topdocs = searcher.search(query, nrofdocstoreturn);        }      }