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From Spico Florin <spicoflo...@gmail.com>
Subject Faulty example for rebalancing in the wiki documentation about understanding storm paralellism
Date Wed, 05 Feb 2014 11:44:58 GMT
Hello!
  In the wiki documentation regarding the storm parallelism

https://github.com/nathanmarz/storm/wiki/Understanding-the-parallelism-of-a-Storm-topology

the given example command

storm rebalance mytopology -n 5 -e blue-spout=3 -e yellow-bolt=10

will not have any effect in terms of changing the number of executors
for any mentioned component,
(keeping into account that the topology has been started with these
hints blue-spout=2 and yellow-bolt=6).

topologyBuilder.setSpout("blue-spout", new BlueSpout(), 2); // set
parallelism hint to 2

topologyBuilder.setBolt("yellow-bolt", new YellowBolt(), 6)
               .shuffleGrouping("green-bolt");

As it is mentioned in the documentation, when you don't explicitly
specify the number of tasks

then the defaults will be equal with the number of the executors. In
our case the number of
tasks for the blue-spout is 2 and the number of yellow-bolt 6.
Since the condition should hold number_of_executors <=
number_of_tasks, our command

,that is trying to increase the numbers of blue-spout and yellow-bolt
above the number of the existing tasks, will not have any effect.

The only command that will take effect will be to decrease those numbers.

Hope that these help and the documentation will be corrected in the wiki.

Thanks.

Regards,

 Florin

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