Justin, what I suggest is that for QUORUM consistent level, the block for write should be (num_replica/2)+1, this is same as today, but for read request, we just need to access (num_replica/2) nodes, which should provide enough strong consistency.
Dikang. On Thu, Jun 8, 2017 at 7:38 PM, Justin Cameron <jus...@instaclustr.com> wrote: > 2/4 for write and 2/4 for read would not be sufficient to achieve strong > consistency, as there is no overlap. > > In your particular case you could potentially use QUORUM for write and TWO > for read (or vice-versa) and still achieve strong consistency. If you add > additional nodes in the future this would obviously no longer work. Also > the benefit of this is dubious, since 3/4 nodes still need to be accessible > to perform writes. I'd also guess that it's unlikely to provide any > significant performance increase. > > Justin > > On Fri, 9 Jun 2017 at 12:29 Dikang Gu <dikan...@gmail.com> wrote: > >> Hello there, >> >> We have some use cases are doing consistent read/write requests, and we >> have 4 replicas in that cluster, according to our setup. >> >> What's interesting to me is that, for both read and write quorum >> requests, they are blocked for 4/2+1 = 3 replicas, so we are accessing 3 >> (for write) + 3 (for reads) = 6 replicas in quorum requests, which is 2 >> replicas more than 4. >> >> I think it's not necessary to have 2 overlap nodes in even replication >> factor case. >> >> I suggest to change the `quorumFor(keyspace)` code, separate the case for >> read and write requests, so that we can reduce one replica request in read >> path. >> >> Any concerns? >> >> Thanks! >> >> >> -- >> Dikang >> >> -- > > > *Justin Cameron*Senior Software Engineer > > > <https://www.instaclustr.com/> > > > This email has been sent on behalf of Instaclustr Pty. Limited (Australia) > and Instaclustr Inc (USA). > > This email and any attachments may contain confidential and legally > privileged information. If you are not the intended recipient, do not copy > or disclose its content, but please reply to this email immediately and > highlight the error to the sender and then immediately delete the message. > -- Dikang
