> Now we need an explanation of "map" -- can you supply it?

The "map" mode runs all tasks with a TableScan operator inside LLAP instances 
and all other tasks in Tez YARN containers. This is the LLAP + Tez hybrid mode, 
which introduces some complexity in debugging a single query.

The "only" mode is so far the best option since, the LlapDecider runs very late 
in the optimizer order the earlier optimizers need to hedge their bets on 
whether LLAP will finally be used for a vertex or not. The "only" mode sort of 
short-cuts that by assuring all optimizers that it is "LLAP or Bust!".

Cheers,
Gopal



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