In dynamo's paper ,it says:

Each key, k, is assigned to a coordinator node .
The coordinator is in charge of the replication of the data items that fall within its range.

On Fri, Sep 3, 2010 at 2:56 PM, Benjamin Black <b@b3k.us> wrote:
On Thu, Sep 2, 2010 at 8:19 PM, Ying Tang <ivytang0812@gmail.com> wrote:
> 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 ?

The coordinator node is the proxy node.

> 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 ?

Depends on the CL requested.  QUORUM and ALL cause the RR to be
performed by the coordinator.  ANY and ONE cause RR to be delegated to
one of the replicas for the key.

> 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 ?
>

For writes, the coordinator sends the writes directly to the replicas
regardless of CL (rather than delegating for weakly consistent CLs).

> 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?
>

Sorry, I can't even parse this.


b



--
Best regards,

Ivy Tang