with NRT reader/writer, emptying an index using:
writer.deleteAll()
writer.commit()
doesn't release all allocated memory.

for example the following code will generate a memory leak:

/**

• Reveals a memory leak in NRT reader/writer<br>
• The following main() does 10K cycles of:
• <ul>
• <li>Add 10K empty documents to index writer</li>
• <li>commit()</li>
• <li>open NRT reader over the writer, and immediately close it</li>
• <li>delete all documents from the writer</li>
• <li>commit changes to the writer</li>
• </ul>
• Running with -Xmx256M results in an OOME after ~2600 cycles
  */
  public static void main(String[] args) throws Exception {
  RAMDirectory d = new RAMDirectory();
  IndexWriter w = new IndexWriter(d, new IndexWriterConfig(Version.LUCENE_33, new KeywordAnalyzer()));
  Document doc = new Document();

for(int i = 0; i < 10000; i++) {
for(int j = 0; j < 10000; ++j)

w.commit();
IndexReader.open(w, true).close();

w.deleteAll();
w.commit();
}

w.close();
d.close();
}