SB - Its expensive to start a conversation
I've just mentioned Remus's post on service broker procedures. The other thing that came up when looking at the conversation group size was the time it took to load the queue. This set of figures shows the load time, the first is the number of conversations and the second the number of messages per conversation, and the final number, the time it took in seconds.
1x10000 = <1
10x1000 = <1
100x100 = 1.5-2.5
1000x10 = 5.8-6.7
10000x1 = 45-52
It is clear that the overhead of creating a dialog for a conversation is neglible compared to the rest of the code to send the message, when the conversation group size is high.
However when the number of conversations increase and the number of messages per conversation decreases, it is clear the overhead of the extra dialogs is huge.
This adds further weight to my argument that you need to put as many messages in your conversation groups as possible, if you are batch processing messages.
Have a look at Roger Walters blog on recycling dialogs