Doing a little more research on document numbers, I had thought that the maximum document number was 2^30-1 or Integer.MAX_INT, but... I see that IndexReader.numDocs, maxDoc, and the corresponding IndexWriter methods return the number of documents as an int, so since document numbers start at zero, the number of documents is actually limited to 2^30-1, so the highest document number is limited to 2^30-1 minus another 1 or 2^30-2.
-- Jack Krupansky
