title: Difference in elapsed time of the query where everything in the trace seems to be identical
body: <p>While analysing the traces of the program , one before and one which I have run after creating two new indexes, I found some queries which are now having high runtime compared to previous run(which are not using any of the new indexes i have created and have identical execution plans). </p>
  
  <p>One particular query is :</p>
  
  <pre><code>SELECT GP.PERIOD_YEAR, GP.PERIOD_NAME, GP.PERIOD_YEAR || '-' || 
  LPAD(GP.PERIOD_NUM, 2, '0') 
  FROM
  GL_PERIODS GP WHERE GP.PERIOD_TYPE = :B3 AND GP.PERIOD_SET_NAME = :B2 AND 
  GP.ADJUSTMENT_PERIOD_FLAG = 'N' AND TRUNC (:B1 ) BETWEEN TRUNC 
  (GP.START_DATE) AND TRUNC (GP.END_DATE)
  
  Before Stats:
  call     count       cpu    elapsed       disk      query    current        rows
  ------- ------  -------- ---------- ---------- ---------- ----------  ----------
  Parse        1      0.00       0.00          0          0          0           0
  Execute 1738112     31.63      31.26          0          0          0           0
  Fetch   1738112    778.18     780.36         17    6952448          0     1738112
  ------- ------  -------- ---------- ---------- ---------- ----------  ----------
  total   3476225    809.81     811.63         17    6952448          0     1738112
  
  After Stats:
  call     count       cpu    elapsed       disk      query    current        rows
  ------- ------  -------- ---------- ---------- ---------- ----------  ----------
  Parse        1      0.00       0.00          0          0          0           0
  Execute 1738112     75.80      76.87          0          0          0           0
  Fetch   1738112   1490.70    1499.47         17    6952448          0     1738112
  ------- ------  -------- ---------- ---------- ---------- ----------  ----------
  total   3476225   1566.50    1576.36         17    6952448          0     1738112
  </code></pre>
  
  <p>And wait events for this query are </p>
  
  <ol>
  <li>db file sequential read,</li>
  <li>latch: cache buffers chains, </li>
  <li>latch: shared pool</li>
  </ol>
  
  <p>which are not having total wait time of more than a second.</p>
  
  <p>So what I want to know is why this particular query is showing such difference in runtime? What all areas should I look into to get the cause of runtime difference. </p>
  
  <p>I have run the programs in the same instance. Let me know if some more information is required.</p>