You have a cluster running with a FIFO scheduler enabled. You submit a large job A to the cluster,
which you expect to run for one hour. Then, you submit job B to the cluster, which you expect to
run a couple of minutes only.
You submit both jobs with the same priority.
Which two best describes how FIFO Scheduler arbitrates the cluster resources for job and its
tasks?
A.
Because there is a more than a single job on the cluster, the FIFO Scheduler will enforce a limit
on the percentage of resources allocated to a particular job at any given time
B.
Tasks are scheduled on the order of their job submission
C.
The order of execution of job may vary
D.
Given job A and submitted in that order, all tasks from job A are guaranteed to finish before all
tasks from job B
E.
The FIFO Scheduler will give, on average, and equal share of the cluster resources over the job
lifecycle
F.
The FIFO Scheduler will pass an exception back to the client when Job B is submitted, since all
slots on the cluster are use
D is the answer.
A, E are answers for Fair Scheduler.
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The question says 2 right? So Isn’t B and D right answers?
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B and D
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A & D
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Sorry, B & D
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“The FIFO Scheduler places applications in a queue and runs them in the order of submission (first in, first out). Requests for the first application in the queue are allocated first; once its requests have been satisfied, the next application in the queue is served, and so on.” – Hadoop: The Definitive Guide, 4th Edition by Tom White
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Isn’t it B and C
FIFO only schedules the jobs. And once some tasks of the first jobs is finished and the resources are available, it would be given to the second job.
But no one can say which job will finish the execution. If job two is very light, it could actually finish before the first job. Thus the order of execution could actually vary.
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In my opinion it’s B and D
D is obvious. As we know, FIFO runs one task at a time on the cluster,
so since A is submitted first, it’ll take up all the resources, and B can’t be scheduled until A finishes.
FIFO (as it’s name suggests) supports First in First Out scheduling, though priorities are taken into account – which means that if a task with higher priority than task B comes in before A finishes, B wouldn’t run as second (and this would imply answer C to be correct) -,
still in this case, the tasks (A and B) are scheduled on their order of submisson.
So B and D (or C and D depending on the way you look at it)
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I assert that D is also incorrect in that all tasks are guaranteed to START before job B begins. This is because some of the tasks running in Job A may take a long time to finish whereas Job B may have 1 very small, short task. Job B’s short task could begin and end after Job A’s last task begins (but while still running).
Example, Job A has a lot of tasks taking up the whole cluster. As these tasks begin to finish up resources will become available for Job B’s tasks. Since Job B only has one task that takes 30 seconds to run while Job A’s tasks are averaging 12 minutes, it’s likely that Job A will still be running it’s last tasks while Job B takes some freed up resources and completes its single task.
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In my opinion B is the only correct answer and the question is flawed in trying to make you pick two.
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I’ve seen too many cases that the answers from collected comments differ from the original answer, and the collected comments make more sense.
So my question is where the original answers are from and what are their reliability?
Thanks.
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I choose AE
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