Thanks for the feedback. The picture shows a sample request, which is why the coordinator points to two specific nodes. What I was trying to convey that the coordinator node would ensure that 2 of the 3 nodes were written to before reporting success to the client.
I found the article here, it says that the non-blocking writes to the 2nd data center are asynchronous. Is this blog post incorrect as well? http://www.datastax.com/dev/blog/deploying-cassandra-across-multiple-data-centers I'd like to get clarification on how this works and hope to clear up some of the misinformation about multi-DC replication that is out there. I like a lot of the features of cassandra and enjoy working with it, but the amount of conflicting information out on the web is a little disconcerting sometimes. thanks, Rob On Tue, Feb 11, 2014 at 11:02 AM, Andrey Ilinykh <ailin...@gmail.com> wrote: > 1. reply part is missing. > 2. It is confusing a little bit. I would not use term "synchronous". > Everything is asynchronous here. Coordinator writes data to all local nodes > and waits for response from ANY two of them (in case of quorum). In your > picture it looks like the coordinator first makes decision what nodes > should reply. It is not correct. > > > On Tue, Feb 11, 2014 at 9:36 AM, Mullen, Robert <robert.mul...@pearson.com > > wrote: > >> So is that picture incorrect, or just incomplete missing the piece on how >> the nodes reply to the coordinator node. >> >> >> On Tue, Feb 11, 2014 at 9:38 AM, sankalp kohli <kohlisank...@gmail.com>wrote: >> >>> @Mullen, >>> I think your diagram does not answer the question on responses. >>> @Sameer >>> All nodes in DC2 will replay back to the co-ordinator in DC1. So if you >>> have replication of DC1:3,DC2:3. A co-ordinator node will get 6 responses >>> back if it is not in the replica set. >>> Hope that answers your question. >>> >>> >>> On Tue, Feb 11, 2014 at 8:16 AM, Mullen, Robert < >>> robert.mul...@pearson.com> wrote: >>> >>>> I had the same question a while back and put together this picture to >>>> help me understand the flow of data for multi region deployments. Hope that >>>> it helps. >>>> >>>> >>>> On Mon, Feb 10, 2014 at 7:52 PM, Sameer Farooqui < >>>> sam...@blueplastic.com> wrote: >>>> >>>>> Hi, >>>>> >>>>> I was hoping someone could clarify a point about multi-DC replication. >>>>> >>>>> Let's say I have 2 data centers configured with replication factor = 3 >>>>> in each DC. >>>>> >>>>> My client app is sitting in DC 1 and is able to intelligently pick a >>>>> coordinator that will also be a replica partner. >>>>> >>>>> So the client app sends a write with consistency for DC1 = Q and >>>>> consistency for DC2 = Q to a coordinator node in DC1. >>>>> >>>>> That coordinator in DC1 forwards the write to 2 other nodes in DC1 and >>>>> a coordinator in DC2. >>>>> >>>>> Is it correct that all 3 nodes in DC2 will respond back to the >>>>> original coordinator in DC1? Or will the DC2 nodes respond back to the DC2 >>>>> coordinator? >>>>> >>>>> Let's say one of the replica nodes in DC2 is down. Who will hold the >>>>> hint for that node? The original coordinator in DC1 or the coordinator in >>>>> DC2? >>>>> >>>> >>>> >>> >> >
