how to decide how many Cassandra nodes for deploy

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)

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傅, 健

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