It depends on the workload. 

Increase the cache size until you see the hit rate decrease, or see it create memory pressure. Watch the logs for messages that the caches have been decreased. 

Take a look at the Recent Read Latency for the CF. This is how long it takes to actually read data on that node. You can then work out the throughput taking into account the concurrent_readers setting in the yaml. 

Cheers

-----------------
Aaron Morton
Freelance Developer
@aaronmorton

On 3/04/2012, at 4:14 PM, Shoaib Mir wrote:

On Tue, Apr 3, 2012 at 11:49 AM, aaron morton <aaron@thelastpickle.com> wrote:
Take a look at the key cache hit rate in nodetool cfstats. 

One approach is to increase the cache size until you do not see a matching increase in the hit rate.


Thanks Aaron, what do you think will be the ideal cache hit ratio where we want this particular DB server to do around 5-6K responses per second? right now it is doing just 2-3K per second and the cache hit ratio I can see with cfstats is around the 85-90%. Do you think having a higher cache hit ratio around the 95% mark will help with getting a high throughput as well?

cheers,
Shoaib