I see that design doc doesn't talk about plug and play aspect of cost model; and it also doesn't make it clear that cost model described is for Join Algorithm selection; also it doesn't have cost model for MR.
I will update the doc appropriately. Thanks John -- CONFIDENTIALITY NOTICE NOTICE: This message is intended for the use of the individual or entity to which it is addressed and may contain information that is confidential, privileged and exempt from disclosure under applicable law. If the reader of this message is not the intended recipient, you are hereby notified that any printing, copying, dissemination, distribution, disclosure or forwarding of this communication is strictly prohibited. If you have received this communication in error, please contact the sender immediately and delete it from your system. Thank You.
