public long estimate_sum( ) {
      // For short tables, just do the work
      if( _t.length <= 64 ) return sum();
      // For bigger tables, periodically freshen a cached value
      long millis = System.currentTimeMillis();
      if( _fuzzy_time != millis ) { // Time marches on?
        _fuzzy_sum_cache = sum(); // Get sum the hard way
        _fuzzy_time = millis;   // Indicate freshness of cached value
      }
      return _fuzzy_sum_cache;  // Return cached sum
    }
Return the internal counter striping factor.  Useful for diagnosing
performance problems.
jctools-core/src/main/java/org/jctools/maps/ConcurrentAutoTable.java