title: best way to replace redis set value
body: <p>I want to store a key-values type data into redis, values is a set type which means no duplicate value. I opereate in redis like this:</p>
  
  <pre><code>127.0.0.1:6379&gt; sadd a 1 2 3
  (integer) 3
  127.0.0.1:6379&gt; smembers a
  1) "1"
  2) "2"
  3) "3"
  127.0.0.1:6379&gt; sadd a 4 5 6
  (integer) 3
  127.0.0.1:6379&gt; smembers a
  1) "3"
  2) "2"
  3) "4"
  4) "5,"
  5) "1"
  6) "6"
  </code></pre>
  
  <p>I want user set(4,5,6) replace set(1,2,3). </p>