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From Samuel Benz <samuel.b...@switch.ch>
Subject Re: quorum calculation seems to depend on previous selected nodes
Date Tue, 18 Jan 2011 07:15:12 GMT
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.


--
Sam

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