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From Anthony Ikeda <anthony.ikeda....@gmail.com>
Subject Re: Will writes with < ALL consistency eventually propagate?
Date Mon, 07 Nov 2011 12:47:06 GMT
Riyad, I'm also just getting to know the different settings and values myself :)

I believe, and it also depends on your config, CL.ONE Should ignore the loss of a node if
your RF is 5, once you increase the CL then if you lose a node the CL is not met and you will
get exceptions returned. 

Sent from my iPhone

On 07/11/2011, at 4:32, Riyad Kalla <rkalla@gmail.com> wrote:

> Anthony and Jaydeep, thank you for weighing in. I am glad to see that they are two different
values (makes more sense mentally to me).
> 
> Anthony, what you said caught my attention "to ensure all nodes have a copy you may not
be able to survive the loss of a single node." -- why would this be the case?
> 
> I assumed (incorrectly?) that a node would simply disappear off the map until I could
bring it back up again, at which point all the missing values that it didn't get while it
was done, it would slowly retrieve from other members of the ring. Is this the wrong understanding?
> 
> If forcing a replication factor equal to the number of nodes in my ring will cause a
hard-stop when one ring goes down (as I understood your comment to mean), it seems to me I
should go with a much lower replication factor... something along the lines of 3 or roughly
ceiling(N / 2) and just deal with the latency when one of the nodes has to route a request
to another server when it doesn't contain the value.
> 
> Is there a better way to accomplish what I want, or is keeping the replication factor
that aggressively high generally a bad thing and using Cassandra in the "wrong" way?
> 
> Thank you for the help.
> 
> -Riyad
> 
> On Sun, Nov 6, 2011 at 11:14 PM, chovatia jaydeep <chovatia_jaydeep@yahoo.co.in>
wrote:
> Hi Riyad,
> 
> You can set replication = 5 (number of replicas) and write with CL = ONE. There is no
hard requirement from Cassandra to write with CL=ALL to replicate the data unless you need
it. Considering your example, If you write with CL=ONE then also it will replicate your data
to all 5 replicas eventually.
> 
> Thank you,
> Jaydeep
> From: Riyad Kalla <rkalla@gmail.com>
> To: "user@cassandra.apache.org" <user@cassandra.apache.org>
> Sent: Sunday, 6 November 2011 9:50 PM
> Subject: Will writes with < ALL consistency eventually propagate?
> 
> I am new to Cassandra and was curious about the following scenario...
> 
> Lets say i have a ring of 5 servers. Ultimately I would like each server to be a full
replication of the next (master-master-*). 
> 
> In a presentation i watched today on Cassandra, the presenter mentioned that the ring
members will shard data and route your requests to the right host when they come in to a server
that doesnt physically contain the value you wanted. To the client requesting this is seamless
excwpt for the added latency.
> 
> If i wanted to avoid the routing and latency and ensure every server had the full data
set, do i have to write with a consistency level of ALL and wait for all of those writes to
return in my code, or can i write with a CL of 1 or 2 and let the ring propagate the rest
of the copies to the other servers in the background after my code has continued executing?
> 
> I dont mind eventual consistency in my case, but i do (eventually) want all nodes to
have all values and cannot tell if this is default behavior, or if sharding is the default
and i can only force duplicates onto the other servers explicitly with a CL of ALL.
> 
> Best,
> Riyad
> 
> 

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