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From "Hiller, Dean" <Dean.Hil...@nrel.gov>
Subject Re: Replication Factor and Consistency Level Confusion
Date Wed, 19 Dec 2012 16:14:42 GMT
Ps, you may be getting a bit confused by the way.  Just think if you have
a 10 node cluster and one node is down  and you do CL=2Š..if the node that
is down is where your data goes, yes, you will fail.  If you do CL=quorum
and RF=3 you can tolerate one node being downŠIf you use astyanax, I think
they have an implementation that will switch the CL level to lower when a
node is out so the writes will still work which is quite nice.  (ie. Write
fails, switch to CL lower and write again or same with the read).

Dean

On 12/19/12 9:07 AM, "Vasileios Vlachos" <vasileiosvlachos@gmail.com>
wrote:

>Hello All,
>
>We have a 3-node cluster and we created a keyspace (say Test_1) with
>Replication Factor set to 3. I know is not great but we wanted to test
>different behaviors. So, we created a Column Family (say cf_1) and we
>tried writing something with Consistency Level ANY, ONE, TWO, THREE,
>QUORUM and ALL. We did that while all nodes were in UP state, so we
>had no problems at all. No matter what the Consistency Level was, we
>were able to insert a value.
>
>Same cluster, different keyspace (say Test_2) with Replication Factor
>set to 2 this time and one of the 3 nodes deliberately DOWN. Again, we
>created a Column Family (say cf_1) and we tried writing something with
>different Consistency Levels. Here is what we got:
>ANY: worked (expected...)
>ONE: worked (expected...)
>TWO: did not work (WHAAAAT???)
>THREE: did not work (expected...)
>QUORUM: worked (expected...)
>ALL: did not work (expected I guess...)
>
>Now, we know that QUORUM derives from (RF/2)+1, so we were expecting
>that to work, after all only 1 node was DOWN. Why did Consistency
>Level TWO not work then???
>
>Third test... Same cluster again, different keyspace (say Test_3) with
>Replication Factor set to 3 this time and 1 of the 3 nodes
>deliberately DOWN again. Same approach again, created different Column
>Family (say cf_1) and different Consistency Level settings resulted in
>the following:
>ANY: worked (whaaaaat???)
>ONE: worked (whaaaaat???)
>TWO: did not work (whaaaaat???)
>THREE: did not work (expected...)
>QUORUM: worked (whaaaaat???)
>ALL: worked (whaaaaat???)
>
>We thought that if the Replication Factor is greater than the number
>of nodes in the cluster, writes are blocked.
>
>Apparently we are completely missing the a level of understanding
>here, so we would appreciate any help!
>
>Thank you in advance!
>
>Vasilis


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