The first time you run code in a REPL Julia will have to compile it. So starting a new REPL, and trying to solve a very small problem one time will currently be

The first time you run code in a REPL Julia will have to compile it. So starting a new REPL, and trying to solve a very small problem one time will currently be a terrible workflow for Julia (unless you don’t care that it may take a few seconds). If you had run your code again within the same REPL you’d see it runs substantially faster the second time. Likewise, if you had tried to process a large enough matrix or CSV that compilation time should be a minimal subset of the total computing time, and probably not noticeable. It isn’t a language limitation, just a tooling limitation. The startup times have been getting better as Julia develops, but there is still noticeable overhead the first time code gets run in a new REPL...