I admit that I'm no patch expert. The change needed to log the threadpool used is pretty simple:
cvs diff queue.c
Index: queue.c
===================================================================
RCS file: /cvsroot/aolserver/aolserver/nsd/queue.c,v
retrieving revision 1.38
diff -r1.38 queue.c
361c361
< sprintf(name, "-conn:%d-", poolPtr->threads.nextid++);
---
> sprintf(name, "-%s:%d-", poolPtr->name, poolPtr->threads.nextid++);
So line 361 gets a little change.
I also notice that your mainpool threadpool only maps "/" for the method POST. I haven't experimented, but this might not do anything but url = "/". If you make the change to the queue.c, maybe report if mainpool is used for POST on urls other than "/".
