title: What does Active Sessions and User I/O mean in Oracle Enterprise Manager?
body: <p><img src="https://i.stack.imgur.com/MPA1Z.png" alt="enter image description here"></p>
  
  <p>What does "Active Session" mean? I need to analyze database performance by using this graph taken from Oracle Enterprise Manager (OEM), but I don't understand what is "Active Session" and why there are 22 of them of User I/O? Could someone please explain me with simple language this basics: "Active Session" and "User I/O" in OEM? And what is the relationship between them? </p>