question about when do resource matching in YARN

[wei yan @ Gmail]

Hi, all,

I have a simple question. Currently in YARN, the resource matching is triggered 
by the node manager heartbeat. That is, assignContainers() is only invoked when 
a new heartbeat comes in. Why we don't use resource request triggered 
mechanism? That is, when AM submits allocateRequest, we do the resource 
matching and assign containers.

Does anybody have any idea about this?

thanks,
Wei