synchronized void checkpointNoSIS() throws IOException {
  changeCount.incrementAndGet();
  deleter.checkpoint(segmentInfos,false);
}

synchronized void checkpointNoSIS ( ) throws IOException { changeCount . incrementAndGet ( ) ; deleter . checkpoint ( segmentInfos , false ) ; }
checkpoints with indexfiledeleter , so it ' s aware of new files , and increments changecount , so on close / commit we will write a new segments file , but does not bump segmentinfos . version .
