On 19 March 2012 23:41, Peter Schuller <peter.schul...@infidyne.com> wrote: >>> Using this ring bucket in the CRUSH topology, (with the hash function >>> being the identity function) would give the exact same distribution >>> properties as the virtual node strategy that I suggested previously, >>> but of course with much better topology awareness. >> >> I will have to re-read your orignal post. I seem to have missed something :) > > I did, and I may or may not understand what you mean. > > Are you comparing vnodes + hashing, with CRUSH + pre-partitioning by > hash + identity hash as you traverse down the topology tree?
Yes. I was just trying to illustrate that it's not necessary to have CRUSH doing the partitioning and placement of primary replicas. The same functionality can be achieved by having logically separate placement (a ring with virtual nodes) and a replication strategy which implements the CRUSH algorithm for replica placement. I think you agreed with this further down your previous reply anyway, perhaps I was just being too verbose :) The reason I'm trying to make that distinction is because it will be less work than wholesale replacing the entire distribution logic in Cassandra with CRUSH. I'm not sure if that's exactly what your design is suggesting? -- Sam Overton Acunu | http://www.acunu.com | @acunu
