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From "Hiller, Dean" <>
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).


On 12/19/12 9:07 AM, "Vasileios Vlachos" <>

>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!

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