+1 to make it simple to let multiple threads help with commit/refresh
operations.
IW.yield is a simple way to achieve it, matching (roughly) how IW's
commit/refresh work today, hijacking incoming indexing threads to gain
concurrency. I think this would be a small change?
Adding an ExecutorServic
I noticed that commit() was taking an inordinately long time. It turned out
IndexWriter was flushing using only a single thread because it relies on
its caller to supply it with threads (via updateDocument, deleteDocument,
etc), which it then "hijacks" to do flushing. If (as we do) a caller
indexes
