I'm trying to tune the heap size in my 10 node cluster (currently on 0.8.4). Each machine has 64GB of RAM so there's plenty of room, and I would like to find the "correct" number. Following the tuning guide on the DataStax developer guide, I see my heap should be = (memtable_total_space_in_mb) + 1GB + (cache_size_estimate), and since I have row caching disabled it seems I should only be concerned with the size of my key cache. My question is, how do determine the size of the key cache? I see in the guide it says to take the reported size of the cache and multiply it by 10-12, but unless I'm mistaken the cache size is reported by nodetool cfstats in terms of the number of keys, so I don't understand where the size of my keys fits into this equation (if at all), and I'm not sure why the current cache size is the relevant number instead of the maximum possible cache size.
Thanks in advance.