title: Bloomberg Session timeout?
body: <p>As informed by the example in the Bloomberg APIv3, i need to start a Bloomberg session to open a service, then i need to use the service to create a request. </p>
  
  <p>My question is, if my program sent a request, got the answer, and then after a while it might need to send another request. In this situation, how do i determine whether the Session/Service is still good to use to send the request, or do i need to  start another session?</p>
  
  <p>Does it cost much to start a session?
  Dose it bother Bloomberg's server if i start and stop a session quite often？</p>
  
  <p>BTW, when i'm retrieving historical data, what's the proper size of data to ask for within a single request?</p>
  
  <p>Thanks a lot for your kind help!</p>