We're storing exceptions captured by Twisted on the media pipeline cache, but we're also using the defer.returnValue method with our own methods decorated with @defer.inlineCallbacks.
The defer.returnValue method passes returned values forward by throwing a defer.DefGenReturn exception, which in its turn extends the BaseException class and is captured by Twisted.
This way, the latest exception stored in the Failure's object may also have an HtmlResponse object in its context attribute. As the Response object also keeps track of the Request object that has originated it, you could figure it out how many RAM we're wasting here.
This could easily lead to a Memory Leak problem when running spiders with Media Pipeline enabled and a particular Request set that tends to raise a significant number of exceptions.
Example triggers: - media requests with 404 status responses - user land exceptins coming from custom middlewares - etc.