incubator-cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From srmore <comom...@gmail.com>
Subject Re: Query a datacenter
Date Tue, 29 Oct 2013 12:57:02 GMT
Thanks Rob that helps !


On Fri, Oct 25, 2013 at 7:34 PM, Robert Coli <rcoli@eventbrite.com> wrote:

> On Fri, Oct 25, 2013 at 2:47 PM, srmore <comomore@gmail.com> wrote:
>
>> I don't know whether this is possible but was just curious, can you query
>> for the data in the remote datacenter with a CL.ONE ?
>>
>
> A coordinator at CL.ONE picks which replica(s) to query based in large
> part on the dynamic snitch. If your remote data center has a lower badness
> score from the perspective of the dynamic snitch, a CL.ONE request might go
> there.
>
> 1.2.11 adds [1] a LOCAL_ONE consistencylevel which does the opposite of
> what you are asking, restricting CL.ONE from going cross-DC.
>
>
>> There could be a case where one might not have a QUORUM and would like to
>> read the most recent  data which includes the data from the other
>> datacenter. AFAIK to reliably read the data from other datacenter we only
>> have CL.EACH_QUORUM.
>>
>
> Using CL.QUORUM requires a QUORUM number of responses, it does not care
> from which data center those responses come.
>
>
>> Also, is there a way one can control how frequently the data is
>> replicated across the datacenters ?
>>
>
> Data centers don't really exist in this context [2], so your question is
> "can one control how frequently data is replicated between replicas" and
> the answer is "no." All replication always goes to every replica.
>
> =Rob
> [1] https://issues.apache.org/jira/browse/CASSANDRA-6202
> [2] this is slightly glib/reductive/inaccurate, but accurate enough for
> the purposes of this response.
>

Mime
View raw message