Yes, it’s easy to accidentally or purposefully do. An example of what I’m talking about is “I’m going to cause an N+1, row lock contention, and slow writes by looping over a list of IDs while holding a transaction open, retrieving information for each, and then doing a single write.” This is something that is shockingly easy to do with an ORM if you don’t know any better, but it’s also one of the easiest problems to solve once you do.
Or, explicitly germane to a language vs. an ORM, something like concatenating strings instead of building them in whatever your language’s method of doing so is. Does it have that big of a performance hit in a vacuum? No, but it also takes no more effort to do it correctly, and small gains add up, so why not do it right from the start?
Or, explicitly germane to a language vs. an ORM, something like concatenating strings instead of building them in whatever your language’s method of doing so is. Does it have that big of a performance hit in a vacuum? No, but it also takes no more effort to do it correctly, and small gains add up, so why not do it right from the start?