So how many GB was it, GB?
None, actually. It was a MySQL problem I created by pruning 6,600+ spam accounts from our user table.
Did you know that when you delete a user, it instigates a cleanup of several different unindexed tables, resulting in tying up the MySQL connection for about 40 seconds per user deleted?
I didn't.
Until after the batch delete.
So the slowness would have persisted for about 72 hours and change to work out on its own. Instead, it lasted about 3 hours because that's how long it took me to figure out where the problem was, research it, find a solution, and implement it.
Those 40 second table cleanups now take about 0.15 seconds, because I manually created indexes for the tables in question.