Detecting problems through logs

For any problem in your running system, there are two kinds of errors that can occur: expected errors and unexpected errors.

Detecting expected errors

Expected errors are errors that are raised by explicitly creating an ERROR log in the code. If an error log is being generated, this means that it reflects a situation that has been planned in advance; for example, you can't connect to the database, or there is some data stored in an old, deprecated format. We don't want this to happen, but we saw the possibility of it happening and prepared the code to deal with it. They normally describe the situation well enough that the issue is obvious, even if the solution isn't.

They are...