docs: public void run() {
      long purged_columns;
      try {
        purged_columns = purgeUIDMeta().joinUninterruptibly();
        LOG.info("Thread [" + thread_id + "] finished. Purged [" + 
            purged_columns + "] UIDMeta columns from storage");
        
        purged_columns = purgeTSMeta().joinUninterruptibly();
        LOG.info("Thread [" + thread_id + "] finished. Purged [" + 
            purged_columns + "] TSMeta columns from storage");
      } catch (Exception e) {
        LOG.error("Unexpected exception", e);
      }
      
    }