code: function recordUnique(name, uniqueId, statistics, aggregations, timestamp, callback) {
          timestamp = timestamp || Date.now();
          // normal record
          if(statistics) {
              var num = Array.isArray(uniqueId) ? uniqueId.length : 1;
              record(name, num, statistics, aggregations, timestamp);
          }
          // record unique
          var multi = redis.multi();
          granularities.forEach(function(gran) {
                  var key = getGranKey(name, gran, timestamp);
                  var expireTime = util.getExpireTime(gran, timestamp);
                  var pfkey = key + ':pf';
                  multi.hset(keyPFKeys, pfkey, expireTime);
                  if(Array.isArray(uniqueId)) {
                      multi.pfadd.apply(multi, [pfkey].concat(uniqueId));
                  } else {
                      multi.pfadd(pfkey, uniqueId);
                  }
                  // recordStats(key);
                  var unitPeriod = gran[0];
                  multi.hincrby(key, 'uni', 0);
                  multi.expire(key, points * unitPeriod / 1000);
          });
          multi.exec(callback || log);
      }
docs: record unique access, like unique user of a period time.
  @param {string | Array} uniqueId one or some uniqueId to be stats