Yes, I saw LOCAL_QUORUM. The definition I saw was: Ensure that the write has been written to <ReplicationFactor> / 2 + 1 nodes, within the local datacenter (requiresNetworkTopologyStrategy)
This will allow a quorum within a datacenter. However, I think this means that if availability zones are racks, that the quorum would still be across availability zones. -Mike On Jul 3, 2012, at 9:22 AM, Robin Verlangen wrote: > Hi Mike, > > I'm not sure about all your questions, however you should take a look at > LOCAL_QUORUM for your question about consistency level reads/writes. > > 2012/7/3 Michael Theroux <mthero...@yahoo.com> > Hello, > > We are currently running a web application utilizing Cassandra on EC2. Given > the recent outages experienced with Amazon, we want to consider expanding > Cassandra across availability zones sooner rather than later. > > We are trying to determine the optimal way to deploy Cassandra in this > deployment. We are researching the NetworkTopologyStrategy, and the > EC2Snitch. We are also interested in providing a high level of read or write > consistency, > > My understanding is that the EC2Snitch recognizes availability zones as > racks, and regions as data-centers. This seems to be a common configuration. > However, if we were to want to utilize queries with a READ or WRITE > consistency of QUORUM, would there be a high possibility that the > communication necessary to establish a quorum, across availability zones? > > My understanding is that the NetworkTopologyStrategy attempts to prefer > replicas be stored on other racks within the datacenter, which would equate > to other availability zones in EC2. This implies to me that in order to have > the quorum of nodes necessary to achieve consistency, that Cassandra will > communicate with nodes across availability zones. > > First, is my understanding correct? Second, given the high latency that can > sometimes exists between availability zones, is this a problem, and instead > we should treat availability zones as data centers? > > Ideally, we would be able to setup a situation where we could store replicas > across availability zones in case of failure, but establish a high level of > read or write consistency within a single availability zone. > > I appreciate your responses, > Thanks, > -Mike > > > > > > > -- > With kind regards, > > Robin Verlangen > Software engineer > > W http://www.robinverlangen.nl > E ro...@us2.nl > > Disclaimer: The information contained in this message and attachments is > intended solely for the attention and use of the named addressee and may be > confidential. If you are not the intended recipient, you are reminded that > the information remains the property of the sender. You must not use, > disclose, distribute, copy, print or rely on this e-mail. If you have > received this message in error, please contact the sender immediately and > irrevocably delete this message and any copies. >
