In many cases all your data is actually in memory, especially when you can distribute your workload across many machines. If all your data is in memory, you'll

In many cases all your data is actually in memory, especially when you can distribute your workload across many machines. If all your data is in memory, you'll very often hit CPU bottlenecks before memory bandwidth issues. Partially because bandwidth, disregarding latency, is just quite high, partially because expression evaluation in postgres isn't that well optimized (yet).