Even a disk-based storage engine may never need to read from disk if you have enough memory, because the operating system caches recently used disk blocks in me

Even a disk-based storage engine may never need to read from disk if you have enough memory, because the operating system caches recently used disk blocks in memory anyway. OT, but this is the premise behind Kafka's log storage as well. Which is why it's great for sequential reads from the front of the log, and not as a general-purpose DB, which too many people want it to be.