> handful of nodes that I write to with a CL of QUORUM (or there abouts).
If your goal is to service reads w/o waiting for remote servers, you probably would want to use LOCAL_QUORUM (quorum within a data center) or ONE for reads. That however assumes an RF of >= 3 in each data center (which means many copies in total if you have many data centers). Carefully plan how many copies you want in each DC, keeping in mind that 3+ is required for LOCAL_QUORUM to be useful, and keeping in mind that if you have only one copy per DC the latency to data will be vastly increased whenever a node is down even if temporarily. And consider whether you require that written data is guaranteed to be visible globally upon subsequent read or not. I don't know the situation, but I suspect some application logic on top of Cassandra is useful for a CDN like situation. At least if you have a lot of data and you care about cost efficiency. If it's okay to just say RF=3 per DC (so e.g. 9 copies for 3 DC:s) and e.g. use LOCAL_QUOROM for reads, and use LOCAL_QUORUM against each DC for writes (or else just having less strict consistency guarantees), then that's easy. It just won't be cost-effective if you start having to scale to lots and lots of data (or writes). -- / Peter Schuller (@scode, http://worldmodscode.wordpress.com)
