[khc]

poked around a bit of that from a previous job, here's what I remember:

1. there's a control process and worker processes

2. on upgrade, control process launches new worker processes from the new binary

3. requests are drained from old worker processes

4. most of the time nginx request handlers allocate from a per-request allocation pool, so requests mostly don't share memory

5. for the cases where there are global states, there's a separate shared memory pool that you need to allocate from (which is kind of hard to work if you are not using built-in nginx primitives)