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From Stephen Connolly <stephen.alan.conno...@gmail.com>
Subject Re: quorum calculation seems to depend on previous selected nodes
Date Tue, 18 Jan 2011 07:59:36 GMT
On 18 January 2011 07:15, Samuel Benz <samuel.benz@switch.ch> wrote:
> On 01/17/2011 09:28 PM, Jonathan Ellis wrote:
>> On Mon, Jan 17, 2011 at 2:10 PM, Samuel Benz <samuel.benz@switch.ch> wrote:
>>>>> Case1:
>>>>> If 'TEST' was previous stored on Node1, Node2, Node3 -> The update
will
>>>>> succeed.
>>>>>
>>>>> Case2:
>>>>> If 'TEST' was previous stored on Node2, Node3, Node4 -> The update
will
>>>>> not work.
>>>>
>>>> If you have RF=2 then it will be stored on 2 nodes, not 3.  I think
>>>> this is the source of the confusion.
>>>>
>>>
>>> I checked the existence of the row on the different serverver with
>>> sstablekeys after flushing. So I saw three copies of every key in the
>>> cluster.
>>
>> If you want to be guaranteed to be able to read with two nodes down
>> and RF=3, you have to read at CL.ONE, since if the two nodes that are
>> down are replicas of the data you are reading (as in the 2nd case
>> here) Cassandra will be unable to achieve quorum (quorum of 3 is 2
>> live nodes).
>>
>
> Now it seems clear to me. Thanks!
>
> I was confused by the fact that: "live nodes" != "replica live nodes"
>
> Correct me if I'm wrong, but even in a cluster with 1000 nodes and RF=3,
> if I shut down the wrong two nodes, i have the same problem as in my
> mini cluster.

Correct

>
>
> --
> Sam
>

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