Sidekiq offers some answers.
Today I’ve noticed that the pages took a bit too much to load. In the last days I already noticed some sluggishness here and there, for instance in the time that it took to Discourse links to render as page titles.
I checked Sidekiq and there were +100 jobs Enqueued + 5 Busy. Almost all of them RSS Polling feeds. I changed the polling periodicity from 10 minutes to 1 hour and deleted the jobs.
Then I checked the server, and this is what happened before and after the change:
My guess (based on this alone, I still haven’t checked the code) is that RSS Polling will send the feeds to the queue, as many as you have. The queue will ensure that there is a reasonable number of simultaneous jobs. But… I guess the risk is that the queue of feeds becomes so long that when the new RSS Poll is engaged, the last one is still running, and this is when things get ugly until there is a reset, but the queue will grow again, and etc.
Please correct me if this analysis is wrong. 
UPDATE: RSS Polling in action, +60 feeds (on a still new community without masive activity and even less during sleeping hours).
