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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: the process of reading and writing
Date Fri, 03 Sep 2010 14:08:37 GMT
To the degree that this suggests that there is a "master" node for
each range, IMO it is a "bug" in the paper.  (There are several of
these.)  Certainly there are no master nodes in Cassandra.

On Fri, Sep 3, 2010 at 12:02 AM, Ying Tang <ivytang0812@gmail.com> wrote:
> 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
>
>
>



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support
http://riptano.com

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