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From Gopal Vijayaraghavan <gop...@apache.org>
Subject Re: Hive query starts own session for LLAP
Date Thu, 28 Sep 2017 02:56:59 GMT

> 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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