There are some problems. 1. Mostly separate address spaces requires changing the TLB on context switch (modern hw lets it be partial). You could use MPKs to sh

There are some problems. 1. Mostly separate address spaces requires changing the TLB on context switch (modern hw lets it be partial). You could use MPKs to share a single address space with fast protection switches. 2. Threads share the global heap, but your heavy threads would require explicitly defined shared writeable memory regions, so presumably each one has its own heap. That's a fair bit of overhead. 3. Failure isolation is more complicated than deciding what to kill. The expand on the last point, Postgres doesn't isolate failures to a single process because they do share memory and might corrupt those shared memory regions. But even if you don't have shared memory failure recovery isn't always easy. Software has to be written specifically to plan for it. You can kill processes because everything in the OS is written around allowing for that possibility, for example, shells know what to do if a sub-process is killed unexpectedly. Killing a heavy thread (=process) is no good if the parent process is going to wait for a reply from it forever because it wasn't written to handle the process going away.