Github user zhuoliu commented on the pull request:
https://github.com/apache/storm/pull/700#issuecomment-139676554
Initial tests on 5 node openstack cluster (1 zk, 1 nimbus, 3 supervisors).
1. Test a normal topology (no congestion happen)
WordCountTopology3 (3 times more workers and executors than original
WordCount).
Without topology running, the zookeeper node's received packets is 5
pack/second;
without BP, the zk load is 20.1 pack/second;
with BP, the zk load is 20.9 pack/second.
This makes sense: if a topology is running fluently (no congestion
happens), the ZK will almost never be accessed by Backpressure procedures.
"almost" is because we have added an additional topo-backpressure recurring
checking with credential thread (just for dealing with the very rare case that
ZK callback fails to proceed), which reads from ZK every 30 seconds.
So 12 workers cause 12/30 = 0.4 pack / second overheads to ZK.
This shows that Backpressure will have minimal additional overheads for any
non-congested topologies.
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