streaming is hard-coded to be single-threaded
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                 Key: CASSANDRA-3549
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3549
             Project: Cassandra
          Issue Type: Bug
            Reporter: Peter Schuller
            Assignee: Peter Schuller
            Priority: Minor


It turns out, after we were scratching our heads as to why we weren't streaming 
as fast as expected when we bootstrapped 24 additional nodes in a 24 node 
cluster, that a node will only ever stream one outgoing file at a time. This is 
because the MessagingService instantiates it's streamExecturor_ in such a way 
that it gets a maximum size of 1.

This is particularly bad because there is no mechanism to ensure that 
destination nodes stream "evenly" from availabe source nodes, so some source 
nodes were dogpiled.

Meanwhile, the streams that were active were bottlenecking (in our case) on the 
destination side due to writes. In the end the aggregate throughput 
bootstrapping in the cluster was far below intended.

Will submit a patch once we've confirmed it seems safe and that there's no 
concurrency issue lurking.


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