public boolean keysEqual(DataTable that) {
        if (this.data.keySet().size() != that.data.keySet().size()) {
            return false;
        }
        return this.data.keySet().equals(that.data.keySet());
    }
@return the sum of all values.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/metrics/DataTable.java