Debugging a graph-builder error was harder than it needed to be, due to the large volume of unrelated logging. Categorizing log lines, I have the following suggestions:

• edge from ... to ... already exists and edge from ... to ... doesn't exist don't seem like a WARN problems. Are they? Do we need to log them at all?
• Getting mutable metadata is another thing where we should log on error, and not log (especially at the WARN level) that we're about to attempt something.