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From "Hiller, Dean" <Dean.Hil...@nrel.gov>
Subject Re: Consistency level for multi-datacenter setup
Date Mon, 03 Jun 2013 20:24:29 GMT
Also, we had to put a fix into cassandra so it removed "slow nodes" from the list of nodes
to read from.  With that fix our QUOROM(not local quorom) started working again and would
easily take the other DC nodes out of the list of reading from for you as well.  I need to
circle back to with my teammate to check if he got his fix posted to the dev list or not.

Later,
Dean

From: srmore <comomore@gmail.com<mailto:comomore@gmail.com>>
Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Date: Monday, June 3, 2013 2:09 PM
To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Subject: Consistency level for multi-datacenter setup

I am a bit confused when using the consistency level for multi datacenter setup. Following
is my setup:

I have 4 nodes the way these are set up are
Node 1 DC 1 - N1DC1
Node 2 DC 1 - N2DC1

Node 1 DC 2 - N1DC2
Node 2 DC 2 - N2DC2

I setup a delay in between two datacenters (DC1 and DC2 around 1 sec one way)

I am observing that when I use consistency level 2 for some reason the coordinate node is
picking up the nodes from other datacenter. My understanding was that Cassandra picks up nodes
which are close by (from local datacenter), determined by Gossip but looks like that's not
the case.

I found the following comment on Datastax website :

"If using a consistency level of ONE or LOCAL_QUORUM, only the nodes in the same data center
as the coordinator node must respond to the client request in order for the request to succeed."

Does this mean that for multi datacenter we can only use ONE or LOCAL_QUORUM if we want to
use the local datacenter to avoid cross datacenter latency.

I am using the GossipingPropertyFileSnitch.

Thanks !


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