Difference between EO & EOIO

EO and EOIO QOS are used for asynch processing of messages.

If you mention EOIO which is Exactly Once In Order, the messages will be processes one after the other in the queue as they are received. So, you can get sequential processing of messages.

When you have EO which is Exactly Once, messages are processed in any order inside the queue.

When you must have tried i guess not many messages must be stuck in the queue, but in real time, when many messages are hitting the Integration Engine ( says 1000's of IDOC's are recived at the same time ), you will be able to see the difference in this.

Use EOIO when you want sequential processing and to maintain the order of prosesing as per business requirements.

What I meant was messages are processed in different Queues for EO and in a single queue for EOIO...

Now consider a case, when 1000 Idocs hit XI and you are using EO.. Messages will be rotued in different  EO queues. Now, if one of the queue fails due to some SYSFAIL error , then all messages in  only that queue will be stuck up , but the messsages in other queues will continue to be processed , so there is no way you can guaraantee sequential processing with EO.

But, when you use EOIO, all messages are processed in a single queue and this way sequential processing is guaranteed.

This subtle difference can be noticed when a number of messages are hitting XI at the same time.