Mind the InnoDB Purge on Queue / Row Deletion Job (else slow queries)

I am starting a blog post series on using indexes — or tables — as queues. I had this series in the back of my mind for some time. This started a few years back when I worked on optimizing a row deletion job (I do not call this a purge job, to avoid confusion with the InnoDB Purge). Such jobs can be generalized to using indexes (or tables) as queues (this is