Why is lucene 4.9 slower than lucene 2.4.1(writing)?

[김승민80]

Hello.

Long time ago, I made writing/reading program by using lucene.

That's version is 2.4.1.

I try to change it(to 4.9.0)

But new version(4.9.0) is slower than old version. (both searching and
writing).

I want to know why it is slower than old version.

and How can i increase speed more than old version.

and if you can,  Please check my sample source.

Thank you.
Best Regards.

[2.4.1 version's source]
=========================================================
main class :
----------------------------------------------------------------
String indexPath = "index";
String docsPath = "D:\\logTest\\lucene2.4";
final File docDir = new File(docsPath);
  PerFieldAnalyzerWrapper analyzers = new PerFieldAnalyzerWrapper(new
KeywordAnalyzer());
  IndexWriter writer = new IndexWriter(docsPath, analyzers);
  indexDocs(writer, docDir);
  writer.commit();
  writer.close();
--------------------------------------------------------------
indexDocs class :

 Field fieldTimeKey = new Field(EpoLogWriterCommonVar.FIELD_TIME_SS,
"EMPTY", Field.Store.YES, Field.Index.NOT_ANALYZED);
 ...
 Document doc = new Document();

    for (double i = 0; i < 3000000; i++) {
doc = new Document();
// make a new, empty document
fieldTimeKey.setValue("111" + i);
...
               doc.add(fieldTimeKey);
...
               writer.addDocument(doc);

if (i % 10000 == 0) {
    writer.commit();
}
===============================================================


[4.9 version's source]
================================================================
main class :
----------------------------------------------------------------
  String indexPath = "index";
String docsPath = "D:\\logTest\\lucene4.0";
  final File docDir = new File(docsPath);

Directory dir = FSDirectory.open(docDir);
Analyzer analy = new KeywordAnalyzer();
PerFieldAnalyzerWrapper analyzer = new PerFieldAnalyzerWrapper(analy);
IndexWriterConfig iwc = new IndexWriterConfig(Version.LUCENE_4_9, analyzer);
  IndexWriter writer = new IndexWriter(dir, iwc);
  indexDocs(writer, docDir);
  writer.commit();
  writer.close();
--------------------------------------------------------------

indexDocs class :

 Document doc = new Document();
 StringField fieldTimeKey = new
StringField(EpoLogWriterCommonVar.FIELD_TIME_SS, "EMPTY", Field.Store.YES);
    for (double i = 0; i < 3000000; i++) {

doc = new Document();
// make a new, empty document
fieldTimeKey.setStringValue("111" + i);
...
               doc.add(fieldTimeKey);
...
               writer.addDocument(doc);

if (i % 10000 == 0) {
    writer.commit();
}
===============================================================