title: Execution plan cost estimation
body: <p>There is a problem in which i have to update a table with millions of record based on certain conditions.I have written a long shell script and SQL statements to do it.To check the performance , i plan on using explain plan ,studying it from <a href="http://docs.oracle.com/cd/B10500_01/server.920/a96533/ex_plan.htm#19259" rel="nofollow">http://docs.oracle.com/cd/B10500_01/server.920/a96533/ex_plan.htm#19259</a></p>
  
  <p>Here it is written that "Execution plans can differ due to the following:"
  Different Costs->
  Data volume and statistics
  Bind variable types
  Initialization parameters - set globally or at session level</p>
  
  <p>Here i dont understand how <strong>Initialization parameters - set globally or at session level</strong> affects execution plan.
  can anybody explain this?
  Also is there any other way i can check the SQL statements for performance other than explain plan or autotrace.</p>