Manual:$wgMathCheckFiles

Details
Normally when generating math images, we double-check that the directories we want to write to exist, and that files that have been generated still exist when we need to bring them up again.

This lets us give useful error messages in case of permission problems, and automatically rebuild images that have been lost.

On a big site with heavy NFS traffic this can be slow and flaky, so sometimes we want to short-circuit it by setting this to false.