title: Query Running Slow Post Upgrade to 18c
body: <p>I have a few queries which were running fine for a long time in 12c but post upgrade to 18c they have started to take exponential more time. The DB parameters are same for both 12c and 18c DB. One thing I could see in OEM was that there is a lot of difference in between Estimated and Actual Rows </p>
  
  <p><a href="https://i.stack.imgur.com/mdXic.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mdXic.png" alt="enter image description here"></a> </p>
  
  <p>I have gathered stats on tables using, but still issue persists.  </p>
  
  <pre><code>dbms_stats.gather_table_stats(ownname =&gt; USER, tabname =&gt; 'XYZ',
  method_opt=&gt; 'for all indexed columns size skewonly', granularity =&gt; 'ALL', degree =&gt; 8 ,
  cascade =&gt; true,estimate_percent =&gt; 15);
  </code></pre>
  
  <p>Both DB's are running on same data in tables.</p>