Difference between Client and TIBCO EMS Explicit Client Acknowledge mode?Lets take an Example !!A Queue has 5 pending messges. Assume Queue name =sampleClient Ack:-We have an Option to give a session number . Give it as 1.Now run the reciever with out giving confirm activty in Process Definition.(Ex:-Just use Queue Reciever and End)Create a break point before the END activity. so that u can have the stop control on the process.If you run the process, then you can see 1st message will come for the first and when it comes to END activity , we need to run the process from break point .then once after success completion of first message instance second instance will create automatically by the process.Now , if you see the message , its nothing but the 1st messsage because we have not given the acknowledgement , so process keep on trigger with the same messageNow you include confirm activity in process and run it, now you can see each messsge will process in each instance, means totally 5 instances will be created by process for 5 messages and finally process ends.Hence we can conclude that session gets blocked by client acknowledgement mode.So in the above case unless if we give the acknowledge for the first message , 2nd message wont come from EMS server.EMS Explicit Ack:-In this mode , session wont be blocked.Now if we take the same scenario , i mean 5 pending message in sample queue.If we use the Explicit Acknowledge mode in the receiver side without confirm activity and run the process.Immediately 5 instances will be created on the same session and once if one instance complete with out confirm then all the messages will be re-delivered from EMS server.It means session wont gets blocked. but only concern is if we process couple of messages in same session and if we fail to give confirm for one message then all the messages again gets re-deliver from EMS server even though we processed rest of messages , so if we use this mode we should make sure that our process should have duplicate message handling. as the session is not blocked in this mode , it works faster than client mode.Another Test Scenario: In case of a simple client ack mode, once the msg is delivered, the process flow looks for any available confirm activity configured for this receiver, if it doesnt find any then the msg remains in the EMS server. And since the msg continues to remain in the server, it is picked up again and again by the JMS Q Rcvr activity. To avoid this situation, one needs to configure/ use a confirm activity which should follow this JMS Q Rcvr so that it removes (or acknowledges) the msg once it has been successfully delivered.Now coming to the ems specific mode:Tibco Ems Explicit ack mode In this case, even if one doesnt use a confirm activity for a jms q rcvr activity, the messages are in a locked state after a single delivery, which means that EMS server doesnt allow the picking up of the same message again for that session. It assumes that the messages will be explicitly removed (acknowledged) at a later point of time in the process flow. In case we do not remove these messages before the session ends, it will be reprocessed and delivered again during the next session.