@Override
    public String toString() {

        return "UpdateOrInsertStream{" +
                "onUpdateExpression=" + onUpdateExpression +
                ", updateSet=" + updateSetter +
                '}';
    }
Query output stream try to update table else insert into it
modules/siddhi-query-api/src/main/java/io/siddhi/query/api/execution/query/output/stream/UpdateOrInsertStream.java