genmai.go
func (db *DB) SetLogOutput(w io.Writer) {
	if w == nil {
		db.logger = defaultLogger
	} else {
		db.logger = &templateLogger{w: w, t: defaultLoggerTemplate}
	}
}
func (db *DB) SetLogOutput(w io.Writer) {
	if w == nil {
		db.logger = defaultLogger
	} else {
		db.logger = &templateLogger{w: w, t: defaultLoggerTemplate}
	}
}
// SetLogOutput sets output destination for logging.
// If w is nil, it unsets output of logging.