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From Riyad Kalla <>
Subject Re: Will writes with < ALL consistency eventually propagate?
Date Tue, 08 Nov 2011 19:49:32 GMT

It sounds what I might want to deploy is a ring-per-datacenter in this case
and have each data center replicate to one another (to ensure they all have
full copies of the data) but inside of data-center-specific ring, have a
handful of nodes that I write to with a CL of QUORUM (or there abouts).

I've not looked at setting up rings to replicate with each other before...
is that process pretty well documented/explained or is this a black box
that I am slowly wading into?

(watching Andrew's talk from Acunu now to get a better idea of this).


On Mon, Nov 7, 2011 at 10:20 PM, Peter Schuller <
> wrote:

> > Thanks for the additional insight on this -- think of a CDN that needs to
> > respond to requests, distributed around the globe. Ultimately you would
> hope
> > that each edge location could respond as quickly as possible (RF=N) but
> if
> > each of the ring members keep open/active connections to each other, and
> a
> > request comes in to an edge location that does not contain a copy of the
> > data, does it request the data from the node that does, then cache it (in
> > the case of more requests coming into that edge location with the same
> > request) or does it reply once and forget it, requiring *each* subsequent
> > request to that node to always phone back home to the node that actually
> > contains it?
> > The CDN/edge-server scenario works particularly well to illustrate my
> goals,
> > if visualizing that helps.
> > Look forward to your thoughts.
> Nodes will never cache any data. Nodes have the data that they own
> according to the ring topology and the replication factor (to the
> extent that the data has been replicated); the node you happen to talk
> to is merely a "co-ordinator" of a request; essentially a proxy with
> intelligent routing to the correct hosts.
> In the CDN situation, if you're talking about e.g. having a group of
> servers in one "place" (network topologically distinct location, such
> as geographically distinct) then a better fit than RF=N is probably to
> use multi-site support and say that you want a certain number of
> copies for each location and have all clients talk to the most local
> "site".
> But that's assuming you want to try to model this using just
> Cassandra's replication to begin with. Dynamically caching wherever
> data is accessed is a good idea for a CDN use-case (probably), but is
> not something that Cassandra does itself, internally. It's really
> difficult to know what the best solution is for a CDN; and in your
> case you imply that it's really *not* a CDN and it's just an analogy
> ;)
> --
> / Peter Schuller (@scode,

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