We’ve fixed the site issues for now. I thought the “recent comments” feed had been disabled. It had not, and that was causing the bad performance. The hosting people redirected any hits on that feed to Google. Maybe Red State or Instapundit would have been a better choice.
Here’s the issue in a nutshell: when WordPress has to do anything with comments, it must plow through the 3 million comments that we’ve had at this site in the years since it started.
What would be ideal would be to have some kind of WordPress archiving plugin that would put 2.9 million of those comments in an read-only “archived comments” table, which would be used when someone pulls up an old post. The other 100K or so comments would be stored in a read/write “active comments” table.
I’ve searched high and low for something like that, and haven’t been able to find it. Does anyone who’s done big WordPress sites have a clue where we could find something like that?