On Thu, Feb 11, 2010 at 3:29 PM, B. Todd Burruss <bburr...@real.com> wrote: > when using rack aware, RF=3, W=QUORUM ... does a write block until > response from both data centers?
Quorum of 3 means 2, so it will block for first 2 replies, which usually won't include the other DC. BUT, remember it's asymmetrical. Say you have replicas A C in DC1 and B in DC2. Then clients using QUORUM read/write talking to nodes in DC1 won't have to wait for a reply from B, but clients using QUORUM in DC2 will have to wait for either A or C since there is only one replica in DC2. This is the motivation for the [unfinished] DatacenterShardStrategy and the associated DCQUORUM consistency level -- the idea is, wait for a quorum of the nodes _in the same data center that the client is talking to_. -Jonathan
