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From srowen <>
Subject [GitHub] spark issue #18874: [SPARK-21656][CORE] spark dynamic allocation should not ...
Date Thu, 10 Aug 2017 08:39:19 GMT
Github user srowen commented on the issue:
    @tgravescs that's actually progress. You're no longer saying that the goal is to keep
a few executors around just in case ( or
that the problem is waiting on locality (
    I believe then you're saying the problem is what I asked about in
: there should be no way to go to 0 executors when there is any work to do. The scheduler
should never make that decision, even if the min. I agree.
    You're actually saying something stronger: the number of executors should not go below
target, not minimum. If so can we update the description to state it that way? (and if so,
is checking vs min redundant?)
    But what about just fixing the 0 executor case as that is the scenario where no progress
can be made?
    This change is a heuristic with side effects, as noted just above. This means you don't
remove legitimately idle executors that the scheduler won't use. It harms the common case,
though probably marginally. It's behavior change.
    It helps a case only where the driver is stuck for periods longer than an executor idle
timeout. I think you have bigger problems if this is the case, right? If you have 60s GC pauses,
you need to tune GC (or, idle timeout), but it's fair to have to tune _something_ if you don't
like the slowdown from executors having to be reallocated.
    Is this a good tradeoff? I don't think so, but don't feel extreme about it.
    Is it important to address 0 executors, more narrowly? yes.

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