Can this be taken to mean that: - the practical maximum number of threads to run your single (non-ZEO) zope instance is {number of zodb connections in pool} else you risk deadlock if yes, would upping the number of ZODB connections effectively raise the ceiling - e.g. 12 ZODB connections -> 12 threads should perform properly ? Is increasing the number of ZODB cx's possible, let alone advisable? (why the default of 7 - not 6 or 8?) More concretely, is there any good way to increase the request-handling capacity of a standalone instance, beyond the limits imposed by the defaults, without deploying ZEO?
To put it in a very simple way, you should not tweak the threads setting unless you really know what you are doing. If your goal is performance the usual way of going about that is to run ZEO and add ZEO clients as needed.
You're bumping into the very simple fact that there are two items interacting badly: Threads and the connections in the Zope database connection pool. A thread, under normal circumstances, can only do work if it has a connection to work with, and wwill only release the connection when the request is finished. There are 7 connections in the pool by default.
jens