Do I need to close DirectoryReader while using Lucene Near real-time indexing feature

Question

Am using Lucence 4.7.2 and am new to it. I tried looking into the lucene source code, but was not able to find the information. The reason for using near real-time is, while searching the index should be visible withing 1 minute of creation.

I have created the following trying to implement/use lucene NRT (near real-time) feature.

//Code to initialize IndexWriter and Near real-time IndexReader. 
//(DirectoryReader is used as IndexReader(IndexWriter, boolean) contructor is deprecated.
directory = FSDirectory.open(new File("C:/Users/arun/lucene-home/"));
Analyzer analyzer = new StandardAnalyzer(Version.LUCENE_47);
IndexWriterConfig indexWriterConfig = new IndexWriterConfig(Version.LUCENE_47, analyzer);
IndexWriter indexWriter = new IndexWriter(directory, indexWriterConfig);

//NOTE 1
DirectoryReader directoryReader = DirectoryReader.open(indexWriter, true); 

As per documentation of DirectoryReader openIfChanged(DirectoryReader oldReader, IndexWriter writer, boolean applyAllDeletes)

Everytime before performing a search, I create IndexSearcher as below

DirectoryReader newDirectoryReader = DirectoryReader.openIfChanged(directoryReader , indexWriter, true);
IndexSearcher nrtIndexSearcher = new IndexSearcher(newDirectoryreader);

Question:

Will the original DirectoryReader "directoryReader " stated in the above code with comment "NOTE 1" be closed by lucene itself? I mean the DirectoryReader implementation or the class that used in it?

If not, how do I track if the IndexSearcher that was created from the DirectoryReader is still being referenced before closing DirectoryReader.

Note: I will not be able to use Solr, Please excuse me.

Answer 1

Each IndexReader has to be closed after being used, otherwise you will end up with "Too many open files" exception.

If you are using openIfChanged , you can check reference equality to see if the reader is different or not:

DirectoryReader oldReader = directoryReader;
DirectoryReader newReader = DirectoryReader.openIfChanged(directoryReader);
if ((newReader != null) & (oldReader != newReader)) {
   directoryReader = newReader;
   oldReader.close();
   // need to close the old one
} else {
   // nothing to do
}

Note: if you are using this in a multi-threaded environment, there's a chance the old reader is still in use - so if you close it too early, searches using old reader (searcher, created using this reader) will fail. The cure for this is NRTManager and/or SearcherManager .