You're assuming the dataset is a file you can just mmap there. If it's more complex (built up from a network feed or something) then yes, there is more work involved than just an mmap call, coordinating shm segments is not zero complexity.

But the real impact is if you want to be mutating that data set. The default behaviour of "tear down the entire process on error" can of course be worked around even if you ignore data corruption errors, but not having to do things by hand is the point of managed runtimes in the first place.

Hah. You'd be surprised how few developers actually know that shared memory exists.