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From Ying Tang <ivytang0...@gmail.com>
Subject Re: the process of reading and writing
Date Fri, 03 Sep 2010 07:02:18 GMT
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

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