每次都有评估产线需要多少Cassandra节点的需求，所以写几个简单的公式：
For Write:
Peak WPS For Application * (Applications keyspace replicator factor / Total Cassandra Nodes Per DC) > Max WPS Capacity For Cassandra Single Node:
For Read:
Precondition:
(1) Read Consistency level Take: LocalQuorum
(2) Every table take default configure:
Peak QPS For Application * ((Applications keyspace replicator factor * 0.1 + (Applications keyspace replicator factor/2+1)*0.9 ) / Total Cassandra Nodes Per DC) > Max QPS Capacity For Cassandra Single Node:
Take example:
For One Application On 7 nodes.
For Write:
Peak WPS For Application * (3 / 7 ) < Max WPS Capacity For Cassandra Single Node:
For Read:
Peak QPS For Application * (2.1 / 7 ) < Max QPS Capacity For Cassandra Single Node:
In Short
So if deployed new Casandra DC:
The Cassandra node numbers > max (3* Peak WPS For Application/Max WPS Capacity For Cassandra Single Node, 2.1* Peak QPS For Application/Max QPS Capacity For Cassandra Single Node)