It had nothing to do with my database. Nothing to do with my plugins, or anything else I was doing. (Okay, moving one little command in my config file a little higher up helped somewhat, but that wasn’t the main problem.)
It had everything to do with bots needing to be blocked. Which, you know: you’d think that would be the first thing they’d suggest, since that’s nothing to do with WordPress and everything to do with spammer parasites attacking websites in general, right? I just wish someone had suggested it weeks ago, and saved me the headache.
On the downside, I suspect it’s actually parasites masquerading as Baidu–a bunch of spambots in China, about whom Baidu seem unable or unwilling to do anything–have basically made it necessary (as far as my hosting company is concerned) to block Baidu altogether.
Then again, I don’t expect much of my real (nonspammer) traffic from China is coming via Baidu, so maybe it’s not a real loss. The probably-fake-Baidu isn’t the only bot clocked, it’s just the first (and worst) on the list. I’m not sure about the others. Not sure I’m concerned, either: collectively, they were adding fifty full minutes to my CPU load, and there’s no sensible reason for them to be doing that. I’m now well below my daily limit again.
So… distress over, for now. And I can actually have plugins turned on, and stuff. Whew.