code: private void replaceWithFinishedReaders(List<SSTableReader> finished)
      {
          if (isOffline)
          {
              for (SSTableReader reader : discard)
              {
                  if (reader.getCurrentReplacement() == reader)
                      reader.markObsolete();
                  reader.selfRef().release();
              }
          }
          else
          {
              dataTracker.replaceEarlyOpenedFiles(discard, finished);
              dataTracker.unmarkCompacting(discard);
          }
          discard.clear();
      }
docs: cleanup all our temporary readers and swap in our new ones