Large Groups?

May 4, 2016 at 1:38 PM
Edited May 4, 2016 at 1:39 PM
Browsing Vsync code, I noticed Group.SetLarge() method with a commentary saying:
"Specifies that the user wishes this group to use the large group protocols. Recommended if a group may have more than about 10 members, although in fact the normal protocols should be stable up to at least 100 members."
Where I can find more info on this topic - large group protocols? I watched all youtube videos but don't remember anything on this (probably I just forget or wasn't attentive enough).
I've also noticed, that this protocol isn't compatible with unicast mode. So... what will happened in case we will try to use unicast-only mode with more then 100-members group - performance degradation or something worse?
May 16, 2016 at 12:57 PM
Edited May 16, 2016 at 12:58 PM
I haven't heard of much recent interest in those protocols, although they have been in the system for many years. They do work, and I plan to continue to support them.

With IP multicast, we've used the basic protocols up to about 800 members, in its normal mode. The main issue is that getting the system to start up can be tricky at that scale. You need to switch to the master/worker startup pattern.

I agree that unicast-only would tend to hit limits at some scale but I honestly don't know what that point will be. Probably more than 100 members, but at some scale in unicast-only mode, you would start to see instability and false failure detections. The large group protocols should get a lot further before collapsing, whether in unicast more or multicast mode.