Cloud-based support for Massively Multiplayer Online Role-Playing Games

Massively Multiplayer Online Role-Playing Games (MMORPGs) are very sophisticated applications, which have significantly grown in popularity since their early days in the mid́90s. Along with growing numbers of users the requirements on these systems have reached a point where technical problems become a severe risk for the commercial success. Within the CloudCraft project we investigate how Cloud-based architectures and data management can help to solve some of the most critical problems regarding scalability and consistency. In this work, we describe an implemented working environment based on the Cassandra DBMS and some of the key findings outlining its advantages and shortcomings (e.g., guarantee of game consistency) for the given application scenario. As outlined for instance by the CAP theorem [GL02], achieving consistency guarantees within a 100% available and fault-tolerant distributed system is impossible. Nevertheless, in real-life applications actual properties are neither black nor white and the degree of fulfillment of requirements depends on the likelihood of failures and communication parameters of distributed systems. While typical Cloud-based applications weaken consistency in accordance with less strict applications requirements, strong consistency can also be achieved, for instance by tunable consistency. This, however, often comes with a strong degradation of scalability (performance of growing clusters) and availability. Based on a project investigating the usefulness of Cloud DBMS for MMORPGs we describe how strong consistency can be provided for such a scenario, by still proving a high-level of availability and performance suitable for this specific application. For this purpose we implement a lightweight mechanism to detect failures based on timestamps and only react accordingly if required.