You will almost certainly not be writing your own, until you do. More importantly, understanding this means you'll know the right questions to ask, or even be

You will almost certainly not be writing your own, until you do. More importantly, understanding this means you'll know the right questions to ask, or even be able to say upfront that a certain well-liked product some exec wants to use won't scale, even if the trial with a dataset less than RAM works "really fast!".