tgravescs commented on issue #26284: [SPARK-29415][Core]Stage Level Sched: Add 
base ResourceProfile and Request classes
URL: https://github.com/apache/spark/pull/26284#issuecomment-554543192
 
 
   The fractional stuff was added in separate jira from the original resource 
scheduling stuff. 
   like I mention above its essentially allowing multiple tasks to run on a 
single resource. 
   All our resources require an address with them.  For instance in the case of 
GPU and a machine has say 4 gpus the id could be 0,1,2,4.   If you are using 
fractional and lets say 0.5. This means that you get 2 tasks per GPU. So 2 
tasks would be assigned GPU address 0.  What they do with that is up to the 
task code, but the assumption is that the user knows they configured it this 
way.
   This is why having fraction over 0.5 doesn't make sense. At that point you 
can only have 1 task with a single address so you might as well configure it at 
1.  It doesn't make sense to have 1 task use 3/4 of one gpu and a second task 
use 1/4 or one gpu and 1/2 of another.  To do that you would need more info in 
the assignments and I don't know how a program would really use that right now. 
 Thus why we restricted it.

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