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  1. Lucene - Core
  2. LUCENE-388

[PATCH] IndexWriter.maybeMergeSegments() takes lots of CPU resources



    • Type: Bug
    • Status: Closed
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 2.1
    • Component/s: core/index
    • Labels:
    • Environment:

      Operating System: Mac OS X 10.3
      Platform: Macintosh

    • Bugzilla Id:


      Note: I believe this to be the same situation with 1.4.3 as with SVN HEAD.

      Analysis using hprof utility shows that during index creation with many
      documents highlights that the CPU spends a large portion of it's time in
      IndexWriter.maybeMergeSegments(), which seems to be a 'waste' compared with
      other valuable CPU intensive operations such as tokenization etc.

      Using the following test snippet to retrieve some rows from the db and create an

      Analyzer a = new StandardAnalyzer();
      writer = new IndexWriter(indexDir, a, true);
      connection = DriverManager.getConnection(
      "jdbc:inetdae7:tower.aconex.com?database=<somedb>", "secret",
      String sql = "select userid, userfirstname, userlastname, email from userx";
      LOG.info("sql=" + sql);
      Statement statement = connection.createStatement();
      LOG.info("Executing sql");
      ResultSet rs = statement.executeQuery(sql);
      LOG.info("ResultSet retrieved");
      int row = 0;

      LOG.info("Indexing users");
      long begin = System.currentTimeMillis();
      while (rs.next()) {
      int userid = rs.getInt(1);
      String firstname = rs.getString(2);
      String lastname = rs.getString(3);
      String email = rs.getString(4);
      String fullName = firstname + " " + lastname;
      Document doc = new Document();
      doc.add(Field.Keyword("userid", userid+""));
      doc.add(Field.Keyword("firstname", firstname.toLowerCase()));
      doc.add(Field.Keyword("lastname", lastname.toLowerCase()));
      doc.add(Field.Text("name", fullName.toLowerCase()));
      doc.add(Field.Keyword("email", email.toLowerCase()));
      if((row % 100)==0)

      { LOG.info(row + " indexed"); }

      double end = System.currentTimeMillis();
      double diff = (end-begin)/1000;
      double rate = row/diff;
      LOG.info("rate:" +rate);

      On my 1.5GHz PowerBook with 1.5Gb RAM and a 5400 RPM drive, my CPU is maxed out,
      and I end up getting a rate of indexing between 490-515 documents/second run
      over 10 times in succession.

      By applying a simple patch to IndexWriter (see attached shortly), which defers
      the calling of maybeMergeSegments() so that it is only called every 2000
      times(an arbitrary figure), I appear to get a new rate of between 945-970
      documents/second. Using Luke to look inside each index created between these 2
      there does not appear to be any difference. Same number of Documents, same
      number of Terms.

      I'm not suggesting one should apply this patch, I'm just highlighting the
      difference in performance that this sort of change gives you.

      We are about to use Lucene to index 4 million construction document records, and
      so speeding up the indexing process is in our best interest! If one
      considers the amount of CPU time spent in maybeMergeSegments over the initial
      index creation of 4 million documents, I think one could see how it would be
      ideal to try to speed this area up (at least move the bottleneck to IO).

      I woul appreciate anyone taking a moment to comment on this.


        1. ASF.LICENSE.NOT.GRANTED--IndexWriter.patch
          0.8 kB
          Paul Smith
        2. ASF.LICENSE.NOT.GRANTED--log.optimized.deep.txt
          454 kB
          Paul Smith
        3. ASF.LICENSE.NOT.GRANTED--log.optimized.txt
          183 kB
          Paul Smith
        4. ASF.LICENSE.NOT.GRANTED--log-compound.txt
          136 kB
          Paul Smith
        5. ASF.LICENSE.NOT.GRANTED--lucene.34930.patch
          2 kB
          Paul Smith
        6. ASF.LICENSE.NOT.GRANTED--Lucene Performance Test - with & without hack.xls
          36 kB
          Paul Smith
        7. doron_2_IndexWriter.patch
          1.0 kB
          Doron Cohen
        8. doron_2b_IndexWriter.patch
          1 kB
          Doron Cohen
        9. doron_IndexWriter.patch
          2 kB
          Doron Cohen
        10. yonik_indexwriter.diff
          3 kB
          Yonik Seeley
        11. yonik_indexwriter.diff
          3 kB
          Yonik Seeley



            • Assignee:
              yseeley@gmail.com Yonik Seeley
              psmith@apache.org Paul Smith
            • Votes:
              2 Vote for this issue
              3 Start watching this issue


              • Created: