title: how to improve cache use in mysql when query
body: <p>when I improve the efficiency by using the query as follows:</p>
  
  <pre><code> select retweet_id from mysqlQ3 where user_id ='99963947’;
  </code></pre>
  
  <p>When I googled , I found that I can change the following parameters:    </p>
  
  <pre><code>query_cache_type=2
  query_cache_limit=1M
  query_cache_size=32M
  </code></pre>
  
  <p>But I am curious that when I change query_cache_type from 1 to 2, it even had bad performance for throughput. What happened? Could anyone specify how to improve mysql performance for this specific query like above? </p>
  
  <p>Thank you so much!</p>