[Lucene.Net] Lucene.Net 2.9.4 - Compound File and Multi File Behavior

[Lingam, ChandraMohan J]

I am noticing a behavior where the index is automatically switched to 
multi-file format from compound file format.

It is easy to reproduce on my system.

Basic Steps:

1.  Create an index (default behavior: created as Compound format)

2.  Update the index (after update, Lucene changed index format from Compound 
to Multi-File)


Sample code attached.  After running for the first time, change the create flag 
to false and rerun in update mode.

Is this normal behavior?  I thought Lucene honors the format unless explicitly 
requested to change.  I do not see this behavior in Lucene.Net 2.0 version and 
can observe in 2.9.4 version.

Thanks!
Chandra


        public void CreateDemoIndex()
        {
            Directory dir = FSDirectory.Open(new 
System.IO.DirectoryInfo(@"C:\\temp\lucene101index"));

            IndexWriter w = new IndexWriter(dir
                , new 
Lucene.Net.Analysis.Standard.StandardAnalyzer(Lucene.Net.Util.Version.LUCENE_29)
                , true
                , IndexWriter.MaxFieldLength.UNLIMITED);

            List<Document> docList = new List<Document>();

            Document doc = new Document();
            doc.Add(new Field("animal", "CAT",
                    Field.Store.YES, Field.Index.ANALYZED_NO_NORMS));
            doc.Add(new Field("says", "meow",
                    Field.Store.YES, Field.Index.ANALYZED_NO_NORMS));
            docList.Add(doc);

            doc = new Document();
            doc.Add(new Field("animal", "DOG",
                    Field.Store.YES, Field.Index.ANALYZED_NO_NORMS));
            doc.Add(new Field("says", "woof woof",
                    Field.Store.YES, Field.Index.ANALYZED_NO_NORMS));
            docList.Add(doc);

            doc = new Document();
            doc.Add(new Field("animal", "pig",
                    Field.Store.YES, Field.Index.ANALYZED_NO_NORMS));
            doc.Add(new Field("says", "oink oink",
                    Field.Store.YES, Field.Index.ANALYZED_NO_NORMS));
            docList.Add(doc);

            foreach (Document docInst in docList)
            {
                w.AddDocument(docInst);
            }

            w.Optimize();

            Console.WriteLine("Number of documents in the index: {0}", 
w.MaxDoc());
            w.Close();
            dir.Close();
        }