I have a memcache instance running that has a 90% hit ratio.

How can I estimate how much more memory it needs to get to a 95% hit ratio?

edit:

This question was blocked, but I do not think this is impossible to answer. After all, anyone that's used a caching system HAS answered this question, most likely with trial&error&luck.

I can look at my usage patterns.

I can increase or decrease memory and see how hit rate changes.

Both of these provide data that informs an estimate. But what's a good/better/best way to do this?