Swapping ProcessPoolExecutor for ThreadPoolExecutor gives real memory and IPC wins, but it trades process isolation for new failure modes because many C extensions and native libraries still assume the GIL and are not thread safe.

Measure aggressively and test under real concurrency: use tracemalloc to find memory hotspots, py-spy or perf to profile contention, and fuzz C extension paths with stress tests so bugs surface in the lab not in production. Watch per thread stack overhead and GC behavior, design shared state as immutable or sharded, keep critical sections tiny, and if process level isolation is still required stick with ProcessPoolExecutor or expose large datasets via read only mmap.