After I applied the changes for the "replace robots" feature this morning, the server ran smoothly for about 8 hours. But then something went wrong, and the site started to behave poorly. A big thank you to everyone who alerted me to the problem.
I wasn't able to figure out what went wrong immediately, so I just pulled back the changes and reverted to the previous version of the site. Sorry to have to do that, but it's the safest thing! I'll work on the new feature some more to see if I can figure out what went wrong.
Most of the responses I've had about the feature were positive. So I hope to get it back online soon.