title: is increasing group_concat_max_len to 500000 will cause a performance issue?
body: <p>I have mysql 5.6 installed. </p>
  
  <p>I have a query that uses group_concat to concatenate a list of user ids into one string with ','.  i need to increase the limit of <code>group_concat_max_len</code> to 500000. </p>
  
  <p>will that cause a performance issue? why group_concat is limited in the first place ? should I query each line and concat it on server ?</p>
  
  <p>any information regarding the issue would be greatly appreciated.</p>