public DataTable setMaxValue(DataTable dataTable) {
        dataTable.data.forEach((key, value) -> {
            Long current = this.data.get(key);
            if (current == null) {
                current = value;
            } else {
                if (current < value) {
                    current = value;
                }
            }
            this.data.put(key, current);
        });
        return this;
    }
@return the sum of all values.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/metrics/DataTable.java