flora karniav created FLINK-8414:
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             Summary: Gelly performance seriously decreases when using the 
suggested parallelism configuration
                 Key: FLINK-8414
                 URL: https://issues.apache.org/jira/browse/FLINK-8414
             Project: Flink
          Issue Type: Bug
          Components: Configuration, Documentation, Gelly
            Reporter: flora karniav
            Priority: Minor


I am running Gelly examples with different datasets in a cluster of 5 machines 
(1 Jobmanager and 4 Taskmanagers) of 32 cores each.

The number of Slots parameter is set to 32 (as suggested) and the parallelism 
to 128 (32 cores*4 taskmanagers).

I observe a vast performance degradation using these suggested settings than 
setting parallelism.default to 16 for example were the same job completes at 37 
seconds vs 140 in the 128 parallelism case.

Is there something wrong in my configuration? Should I decrease parallelism and 
-if so- will this inevitably decrease CPU utilization?

Another matter that may be related to this is the number of partitions of the 
data. Is this somehow related to parallelism? How many partitions are created 
in the case of parallelism.default=128? 



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