Finding:
(1) The more time the server run, the slower it becomes. Because the
global table for storing tweets is becoming much larger.
(2) Message length is not related to runtime (performance)
(3) Throughput 1000 is a bottleneck. There is about 10s delay, even
doesn't work.
Throughput 100 works (Now T=1, MaxFollowers=100001, throughput=116.008,
the max tweet frequency is 10 seconds)