What are all possible concurrent Lucene requests?

Otis Gospodnetic

query read doc write delete optimize merge
query Y Y Y Y Y Y
read doc Y Y Y Y Y Y
write Y Y Y N Y Y
delete N Y N Y N N *
optimize Y Y Y N Y Y
merge Y Y Y N Y Y
*Cannot delete when the IndexWriter object is open
IndexWriter.docCount() does not seem to shrink with deletions
Note: the above matrix assumes that a single instance of IndexReader and IndexWriter are used for concurrent operations.

The creator of this matrix is Mark Harwood. c.f. original matrix