Comment 2 for bug 2060804

debug-log is "best effort" and is sourced from a capped collection in mongo. This is separate to any log files written to disk with the associated max file size setting.

The config you might want to try changing is this

// ModelLogsSize is the size of the capped collections used to hold the
// logs for the models, eg "20M". Size is per model.
ModelLogsSize = "model-logs-size"

I would be wary about setting that too high though.