https://academy.datastax.com/courses/ds201-cassandra-core-concepts/internal-architecture-replication
On Fri, Aug 21, 2015 at 11:53 AM, Laing, Michael <michael.la...@nytimes.com> wrote: > 2 is more correct. > > On Fri, Aug 21, 2015 at 11:48 AM, ibrahim El-sanosi < > ibrahimsaba...@gmail.com> wrote: > >> Dear folks, >> >> >> I have doubt on how Cassandra performs a write request; I have two >> scenarios, please read them and ensure which one is correct? >> >> >> Assume we have cluster consists of 4 nodes N1, N2, N3, and N4. As >> Cassandra distributes the nodes in ring topology, the nodes links as >> following: >> >> N-->N-->N3-->N4-->N1 >> >> Also we have replication factor equal to 3 (RF=3), and consistency level >> equals to ALL (CL=ALL). >> >> Client sends write request, W, to coordinator, say N4. The partitioner >> has determined the primary node of W is N1. >> >> What will happen now? >> >> >> *Scenario 1**:* coordinator sends W to N1. Upon receiving W, N1 stores >> it locally (in commitLog and memtable, *please forget about internal >> process*) and acknowledges the coordinator N4. Then N1 sends a copy of W >> to N2 (because N2 is next node in ring from N1 prospective). Upon receiving >> W, N2 stores it locally and sends acknowledgement to N4. Then N2 sends a >> copy of W to N3 (because N3 is next node in ring from N2 prospective). Upon >> receiving W, N3 stores it locally and acknowledges the Coordinator N4. >> Finally as soon as coordinator, N4, receives an acknowledgement from all >> nodes (N1, N2, and N3), it replays to the client. >> >> Note that: if scenario 1 correct, then the latency will be 4 rounds (N4 >> -->N1-->N2-->N3-->N4 ----client). >> >> >> >> *Scenario 2:* coordinator, N4, broadcasts W to N1, N2, and N3 (N4-->N1, >> N4-->N2, N4-->N3). Then replicas (N1, N2, and N3) store W locally and >> acknowledge to N4. When N4 receives all ACKs, it replays to client. >> >> >> >> Can anyone confirm which scenario is correct in Cassandra? >> >> >> >> Regards? >> >> >> >> Ibrahim >> > >
