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From "Daniel Naber (JIRA)" <>
Subject [jira] Commented: (LUCENE-388) [PATCH] IndexWriter.maybeMergeSegments() takes lots of CPU resources
Date Mon, 14 Aug 2006 23:06:16 GMT
    [ ] 
Daniel Naber commented on LUCENE-388:

I just see that this OOM is not exactly reproducible. I would have expected that it always
happens when it has happened once when indexing the same data with the same settings (though
not necessarily at the same time). But that doesn't seem to be the case. I use Java 1.4.2,
-Xmx2M, writer.setMaxBufferedDocs(50) and I am indexing 2200 files with the IndexFiles class
from the Lucene demo package. Also, I let the code run in Eclipse, maybe this has negative
side effects.

So your code is probably okay, although I suggest you set up a similar test case just to be

> [PATCH] IndexWriter.maybeMergeSegments() takes lots of CPU resources
> --------------------------------------------------------------------
>                 Key: LUCENE-388
>                 URL:
>             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
>         Assigned To: Yonik Seeley
>         Attachments: IndexWriter.patch, log-compound.txt, log.optimized.deep.txt, log.optimized.txt,
Lucene Performance Test - with & without hack.xls, lucene.34930.patch, yonik_indexwriter.diff
> 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(
>                 "<somedb>", "secret",
>                 "squirrel");
>         String sql = "select userid, userfirstname, userlastname, email from userx";
>"sql=" + sql);
>         Statement statement = connection.createStatement();
>         statement.setFetchSize(5000);
>"Executing sql");
>         ResultSet rs = statement.executeQuery(sql);
>"ResultSet retrieved");
>         int row = 0;
>"Indexing users");
>         long begin = System.currentTimeMillis();
>         while ( {
>             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){
>        + " indexed");
>             }
>         }
>         double end = System.currentTimeMillis();
>         double diff = (end-begin)/1000;
>         double rate = row/diff;
>"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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