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From "Paul Smith (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-388) [PATCH] IndexWriter.maybeMergeSegments() takes lots of CPU resources
Date Mon, 14 Aug 2006 06:30:17 GMT
    [ http://issues.apache.org/jira/browse/LUCENE-388?page=comments#action_12427818 ] 
            
Paul Smith commented on LUCENE-388:
-----------------------------------

geez, yep definitely don't put this in, my patch was only a 'suggestion' to highlight how
it fixes the root cause of the problem. iIt is interesting that originally, all the test cases
still pass, yet the problems Yonik highlights is real.  Might warrant some extra test cases
to cover exactly those situation, even if this problem is not addressed.

Be great if this could be fixed completely though, but I haven't got any headspace left to
continue research on this one.. sorry :(

> [PATCH] IndexWriter.maybeMergeSegments() takes lots of CPU resources
> --------------------------------------------------------------------
>
>                 Key: LUCENE-388
>                 URL: http://issues.apache.org/jira/browse/LUCENE-388
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Index
>    Affects Versions: CVS Nightly - Specify date in submission
>         Environment: Operating System: Mac OS X 10.3
> Platform: Macintosh
>            Reporter: Paul Smith
>         Attachments: IndexWriter.patch, log-compound.txt, log.optimized.deep.txt, log.optimized.txt,
Lucene Performance Test - with & without hack.xls, lucene.34930.patch
>
>
> 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
> index:
>         Analyzer a = new StandardAnalyzer();
>         writer = new IndexWriter(indexDir, a, true);
>         writer.setMergeFactor(1000);
>         writer.setMaxBufferedDocs(10000);
>         writer.setUseCompoundFile(false);
>         connection = DriverManager.getConnection(
>                 "jdbc:inetdae7:tower.aconex.com?database=<somedb>", "secret",
>                 "squirrel");
>         String sql = "select userid, userfirstname, userlastname, email from userx";
>         LOG.info("sql=" + sql);
>         Statement statement = connection.createStatement();
>         statement.setFetchSize(5000);
>         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()));
>             writer.addDocument(doc);
>             row++;
>             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.

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