Have a look at locator/DatacenterShardStrategy.java.
On Thu, Apr 15, 2010 at 8:16 AM, Ran Tavory <ran...@gmail.com> wrote: > I'm reading this on this > page http://wiki.apache.org/cassandra/ArchitectureInternals : >> >> AbstractReplicationStrategy controls what nodes get secondary, tertiary, >> etc. replicas of each key range. Primary replica is always determined by the >> token ring (in TokenMetadata) but you can do a lot of variation with the >> others. RackUnaware just puts replicas on the next N-1 nodes in the ring. >> RackAware puts the first non-primary replica in the next node in the ring in >> ANOTHER data center than the primary; then the remaining replicas in the >> same as the primary. > > So I just want to make sure I got this right and that documentation is up to > date. > I have two data centers and rack-aware. > When replication factor is 2: is it always the case that the primary replica > goes to one DC and the second replica to the second DC? > When replication factor is 3: First replica in DC1, second in DC2 and third > in DC1 > When replication factor is 4: First replica in DC1, second in DC2, third in > DC1, fourth in DC1 etc > If I have 4 hosts in each DC, which replication factors make sense? > N=1 - When I don't care about losing data, cool > N=2 - When I want to make sure each DC has a copy; useful for local fast > access and allows recovery if only one host down. > N=3 - If I want to make sure each DC has a copy plus recovery can be made > faster in certain cases, and more resilient to two hosts down. > N=4 - Like N=3 but even more resilient. etc > Say I want to have two replicas in each DC, can this be done? >
