title: Oracle query performance degrades over time
body: <p>We have a oracle query which starts experiencing performance degradation after some time.</p>
  
  <p>Let me clarify the situation:</p>
  
  <ol>
  <li>we find that the query is experiencing performance issue.</li>
  <li>someone works on the issue and checks whats wrong. everything looks ok (e.g. the joins, explain plans, indexes, gather stats, DBAs review the query). </li>
  <li>everything is found to be ok.</li>
  <li>DBA consults SQL Tuning advisor &amp; forces a new plan</li>
  <li>query performance improves by 80 to 90 % .</li>
  <li>Everyone is happy </li>
  <li>after a around 40 to 60 days the issue returns :)</li>
  </ol>
  
  <p>The above scenario has repeated twice.</p>
  
  <p>This issue has been noticed only in UAT and PROD in one of the locations (deployments) but not in other. 
  Just to clarify, the issue seems to be with query/db side as we have noticed using Dynatrace. </p>