Recently , i read the paper about Cassandra again . 
And now i have some concepts about  the reading and writing . 

We all know Cassandra uses NWR ,
When read :
the request ---> a random node in Cassandra .This node acts as a proxy ,and it routes the request.
Here , 
1. the proxy node route this request to this key's coordinator , the coordinator then routes request to other N-1 nodes   OR   the proxy routes the read request to N nodes ?
2. If it is the former situation , the read repair occurs on the  key's coordinator ? 
   If  it is the latter , the  read repair occurs on the proxy node ?

When write :
the request ---> a random node in Cassandra .This node acts as a proxy ,and it routes the request.
Here , 
3. the proxy node route this request to this key's coordinator , the coordinator then routes request to other N-1 nodes   OR   the proxy routes the request to N nodes ?


4. The N isn't the data's copy numbers , it's just a  range . In this  N range , there must be W copies .So W is the copy numbers.
So in this N range , R+W>N can guarantee the data's validity. Right?

 


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Best regards,

Ivy Tang