Section: Research Program
DELYS addresses both theoretical and practical issues of Computer Systems, leveraging our dual expertise in theoretical and experimental research. Our approach is a “virtuous cycle,” triggered by issues with real systems, of algorithm design which we prove correct and evaluate theoretically, and then implement and test experimentally feeding back to theory. The major challenges addressed by DELYS are the sharing of information and guaranteeing correct execution of highly-dynamic computer systems. Our research covers a large spectrum of distributed computer systems: multicore computers, mobile networks, cloud computing systems, and dynamic communicating entities. This holistic approach enables handling related problems at different levels. Among such problems we can highlight consensus, fault detection, scalability, search of information, resource allocation, replication and consistency of shared data, dynamic content distribution, and concurrent and parallel algorithms.
Two main evolutions in the Computer Systems area strongly influence our research project:
(1) Modern computer systems are increasingly distributed, dynamic and composed of multiple devices geographically spread over heterogeneous platforms, spanning multiple management domains. Years of research in the field are now coming to fruition, and are being used by millions of users of web systems, peer-to-peer systems, gaming and social applications, cloud computing, and now fog computing. These new uses bring new challenges, such as adaptation to dynamically-changing conditions, where knowledge of the system state can only be partial and incomplete.
(2) Heterogeneous architectures and virtualisation are everywhere. The parallelism offered by distributed clusters and multicore architectures is opening highly parallel computing to new application areas. To be successful, however, many issues need to be addressed. Challenges include obtaining a consistent view of shared resources, such as memory, and optimally distributing computations among heterogeneous architectures. These issues arise at a more fine-grained level than before, leading to the need for different solutions down to OS level itself.
The scientific challenges of the distributed computing systems are subject to many important features which include scalability, fault tolerance, dynamics, emergent behaviour, heterogeneity, and virtualisation at many levels. Algorithms designed for traditional distributed systems, such as resource allocation, data storage and placement, and concurrent access to shared data, need to be redefined or revisited in order to work properly under the constraints of these new environments. Sometimes, classical “static” problems, (e.g., Election Leader, Spanning Tree Construction, ...) even need to be redefined to consider the unstable nature of the distributed system. In particular, DELYS will focus on a number of key challenges:
- Consistency in geo-scale systems.
Distributed systems need to scale to large geographies and large numbers of attached devices, while executing in an untamed, unstable environment. This poses difficult scientific challenges, which are all the more pressing as the cloud moves more and more towards the edge, IoT and mobile computing. A key issue is how to share data effectively and consistently across the whole spectrum. Delys has made several key contributions, including CRDTs, the Transactional Causal Consistency Plus model, the AntidoteDB geo-distributed database, and its edge extension EdgeAnt.
- Rethinking distributed algorithms.
From a theoretical point of view the key question is how to adapt the fundamental building blocks to new architectures. More specifically, how to rethink the classical algorithms to take into account the dynamics of advanced modern systems. Since a recent past, there have been several papers that propose models for dynamic systems: there is practically a different model for each setting and currently there is no unification of models. Furthermore, models often suffer of lack of realism. One of the key challenge is to identify which assumptions make sense in new distributed systems. DELYS's objectives are then (1) to identify under which realistic assumptions a given fundamental problem such as mutual exclusion, consensus or leader election can be solved and (2) to design efficient algorithms under these assumptions.
- Resource management in heterogeneous systems.
The key question is how to manage resources on large and heterogeneous configurations. Managing resources in such systems requires fully decentralized solutions, and to rethink the way various platforms can collaborate and interoperate with each other. In this context, data management is a key component. The fundamental issue we address in ow to efficiently and reliably share information in highly distributed environments.
- Adaptation of runtimes.
One of the main challenge of the OS community is how to adapt runtime supports to new architectures. With the increasingly widespread use of multicore architectures and virtualised environments, internal runtime protocols need to be revisited. Especially, memory management is crucial in OS and virtualisation technologies have highly impact on it. On one hand, the isolation property of virtualisation has severe side effects on the efficiency of memory allocation since it needs to be constantly balanced between hosted OSs. On the other hand, by hiding the physical machine to OSs, virtualisation prevents them to efficiently place their data in memory on different cores. Our research will thus focus on providing solutions to efficiently share memory between OSs without jeopardizing isolation properties.