You may try to figure out what's the process doing (the backend
obviously, not the frontend (Tcl) process) by attaching to it with
strace.
It's so sad when us poor Windows guys get helpful hints from people assume
that we're smart enough to run *NIX... ;-)
Maybe it's swamped by a context switch storm (but in that case, probably
the other processes would be affected as well).
What is a context switch storm? (and what a great name for a heavy metal
rock band!)
Interestingly enough, last night (after the original post) I watched three
of the processes slow down, one after the other - and then stall for so long
that I had assumed they had frozen. They were all stalled on a message that
I had put in the script that indicated they had never returned from a
commit. I have looked into this, and I believe the commits are actually
going through.
I have a question for you: did you have a long running query keeping
open a transaction? I've just noticed the same problem here, but
things cleaned up immediately when I aborted the long-running
transaction.