MC reported he'd had to restart tomcat-devel several times, so we started looking through logs. I think I've traced the current Tomcat issue to a weird combination of circumstances.
Way back when, the Map of Early Modern London project used to be a PHP app. It had URLs like this:
We turned it into an eXist app, with proper page URLS like this:
I wrote some cunning logic in the app to detect requests to the old URLs and redirect them to the new. However, the logic never fired in normal circumstances, because Apache on the front-end saw ".php" and passed the page off to the PHP interpreter.
To deal with this, I and someone from Systems cooked up an Apache rewrite rule in the virtual host, which would turn the old URL into the new. However, it's not very sophisticated; it treats search parameters very crudely, so it turns this:
which throws up errors when eXist sees it, naturally. Now, it turns out that this particular URL, presumably along with some other similar ones, had been links on the old site way back when, and are now in places such as archive.org, and some bot somewhere has been hitting these URLs, and generating a lot of errors.
I think at this point in time it might make sense to revisit that old rewrite rule and make it much simpler, so that it converts anything which contains the string:
and doesn't worry about trying to parse it at all. Wrote to MC to see if he thinks that makes sense.