I am trying to figure out something that I just cannot find a good answer to.
If I have say a REDIS cache (or some external in-memory cache) sitting in a data center, and an application server sitting in the same data center, what will be the speed of the network connection (latency, throughput) for reading data between these two machines?
Will the network "speed", for example, be still at least an order of magnitude higher than the speed of the RAM that is seeking my data out of the cache on REDIS?
My ultimate question is -- is having this all sitting in memory on REDIS actually providing any utility? Contrasted with if REDIS was caching this all to an SSD instead? Memory is expensive. If the network is indeed not a bottleneck WITHIN the data center, then the memory has value. Otherwise, it does not.
I guess my general question is despite the vast unknowns in data centers and the inability to generalize as well as the variances, are we talking sufficient orders of magnitude between memory latency in a computer system and even the best networks internal to a DC that the memory's reduced latencies don't provide a significant performance improvement? I get that that there are many variables, but how close is it? Is it so close that these variables do matter? For example, take take a hyperbolic stance on it, a tape drive is WAY slower than network, so tape is not ideal for a cache.