title: Slow MySQL query on 2 million entries table
body: <p>I'm trying the following query :</p>
  
  <pre><code>SELECT post_id, meta_key, meta_value FROM wp_postmeta WHERE post_id IN (2167635,2167638,2182793,2182800,2195791,2195809,2208830,2208837,2212480,2212486)
  </code></pre>
  
  <p>in a 2 million wp_postmeta table. 
  Using explain shows that i'm using the existint post_id index. But it takes 5 seconds
  to load (which is pretty much unacceptable).</p>
  
  <p>Any ideas on how to optimize that query?.</p>
  
  <p>Thanks in advance.</p>