OakDirectory has to at times perform directory listing specially at the time of opening of index. With DocumentNodeStore such listing of child nodes "might" be slow if there are lots more deleted nodes and GC has not cleared them so far (due to OAK-1557).
As seen in
OAK-2808 Lucene might be creating and deleting lot more files. To speed up such lookup one OakDirectory can save the listing of child nodes as an array property once the writer is closed.