code: public synchronized Segment nextSegment() throws IOException {
          Segment seg = nextSegment(false);
          
          // Remove the writer segment index buffer file.
          File sibFile = getSegmentIndexBufferFile(seg.getSegmentId());
          if(sibFile.exists()) {
              sibFile.delete();
          }
          
          return seg;
      }
docs: Opens the next segment available for read and write.