[plt-scheme] Webserver on Vista, increasing system load

Hi,
I have tested the webserver on Vista Business using JBlitz pro (a
webserver stress test utility). The test requests a page generated by
a Scheme servlet that retrieves an Xml fragment from the eXist
database. The page contains a url that is used by the stress tester to
request the next page. This happens 7 times in sequence (7 pages) and
then the test case restarts with the original URL.
I've tested using 20, 40, 80 and 120 virtual users.
I see the same pattern in all cases:
* the webserver gradually increases its memory use;
* response time gradually increases from around 100 msec to 4 - 5
seconds (after 40 minutes of testing)
* the "System" process gradually claims more time from the processors,
from about 1% up to 50 - 60%

I ran a Perl script that generates exactly the same page, ActiveState
Perl on IIS. It also does the same interaction on the eXist database.
Ran the same JBlitz test script. Response times are similar to the
initial times of the Scheme version, but do not rise during the test
as in Scheme. This seems to rule out that the eXist component is to
blame (memory consumption by eXist is pretty much the same during the
testrun, after the maximum allowed has been reached).

However, the System activities persist after the PLT webserver has
been shut down, causing the Perl response times to be an order of
magnitude higher (when run after PLT has finished). It looks like some
kind of resource is initially claimed by the PLT webserver, and then
is not released, giving the System process a lot of work (whatever it
does).

I lowered the various timeouts in the PLT configuration, with overall
better performance, but no effect on the decline described above.

My questions:
* Any ideas on the cause of this behaviour, and a possible cure?
* Does the same happen under Unix?

Joop Ringelberg