So, for the quorum, what we really want is that there is one overlap among the nodes in write path and read path. It actually was my assumption for a long time that we need (N/2 + 1) for write and just need (N/2) for read, because it's enough to provide the strong consistency.
On Thu, Jun 8, 2017 at 7:47 PM, Jonathan Haddad <j...@jonhaddad.com> wrote: > It would be a little weird to change the definition of QUORUM, which means > majority, to mean something other than majority for a single use case. > Sounds like you want to introduce a new CL, HALF. > On Thu, Jun 8, 2017 at 7:43 PM Dikang Gu <dikan...@gmail.com> wrote: > >> 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 >> >> -- Dikang
