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Date: Wed, 19 Dec 2012 16:07:00 +0000
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Subject: Replication Factor and Consistency Level Confusion
From: Vasileios Vlachos <vasileiosvlachos@gmail.com>
To: user@cassandra.apache.org
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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