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From Bill de hOra <>
Subject Re: replication impact on write throughput
Date Tue, 11 May 2010 19:08:07 GMT
Mark Greene wrote:
> If you have for example, your replication factor equal to the total 
> amount of nodes in the ring, I suspect you will hit a brick wall pretty 
> soon.

Right :) So if we said there was 100 nodes at 5K wps with R=2, then 
would that suggest the cluster can support 250K wps?

Again, I know this is a tad artificial, just trying to understand the 
impact of replication on writes.

> The biggest impact on your write performance will most likely be the 
> consistency level of your writes. In other words, how many nodes you 
> want to wait for before you acknowledge the write back to the client.

I'd agree for any individual client; what I'm after is the overall 
capacity a cluster has over time in the face of replicas. But let's 
assume it's ConsistencyLevel.ONE - how would you think the available 
write capacity degrades?


> On Tue, May 11, 2010 at 12:10 PM, Bill de hOra < 
> <>> wrote:
>     If I had 10 Cassandra nodes each with a write capacity of 5K per
>     second and a replication factor of 2, would that mean the expected
>     write capacity of the system would be ~25K writes per second because
>     the nodes are also serving other nodes and not just clients?
>     I know this is highly simplified take on things (ie no consideration
>     for reads or quorum), I'm just trying to understand what the
>     implication of replication is on write scalability. Intuitively it
>     would seem actual write capacity is total write capacity divided by
>     the replication factor.
>     Bill

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