I only kicked the tires on kdb ages ago, so this may be out of date. At the time k's speed came from holding time series data in memory as simple dense arrays.

I only kicked the tires on kdb ages ago, so this may be out of date. At the time k's speed came from holding time series data in memory as simple dense arrays. The language treats a vector operation like z[] = x[] + y[] as a single operation, and so executes it as one step in the interpreter loop. The actual operation logic is just compiled c code. So despite being a very simple lisp like language, its array orientation lets it be surprisingly speedy for certain kinds of data crunching.