Definitely 2: https://wiki.apache.org/cassandra/ArchitectureInternals http://www.slideshare.net/grro/cassandra-by-example-the-path-of-read-and-write-requests
On Fri, Aug 21, 2015 at 4:54 PM, Laing, Michael <michael.la...@nytimes.com> wrote: > > 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 >>> >> >> >
