Sole constructor, with all settings set to default values.
Does the actual merge, by calling IndexWriter#merge
Create and return a new MergeThread
Called when an exception is hit in a background merge thread
Returns the number of merge threads that are alive, ignoring the calling thread
if it is a merge thr
Wait for any running merge threads to finish. This call is not interruptible as
used by #close().
Sets max merges and threads to proper defaults for rotational or non-rotational
Called from #maybeStall to pause the calling thread for a bit.