Mikael Högqvist

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A lease is a token which grants its owner exclusive access to a resource for a defined span of time. In order to be able to tolerate failures, leases need to be coordinated by distributed processes. We present FaTLease, an algorithm for fault-tolerant lease negotiation in distributed systems. It is built on the Paxos algorithm for distributed consensus, but(More)
We present Stellaris, the information service of the community project AstroGrid-D. Stellaris is the core component of the AstroGrid-D mid-dleware that enables scientists to share their resources, provides access to large datasets and integrates instruments such as robotic telescopes. Besides the many diverse types of resources, the information service also(More)
Several systems adopting Peer-to-Peer (P2P) solutions for resource discovery in Grids have recently been proposed. This report looks at a P2P resource discovery framework aiming to manage various Grid resources and complex queries. Following the discussion on characteristics of Grid resources and related query requirements, a DHT-based framework leveraging(More)
Large-scale distributed systems often require scalable and fault-tolerant mechanisms to coordinate exclusive access to shared resources such as files, replicas or the primary role. The best known algorithms to implement distributed mutual exclusion with leases, such as Multipaxos, are complex, difficult to implement, and rely on stable storage to persist(More)
Time series analysis, as an application for high dimensional data mining, is a common task in biochemistry, meteorology, climate research, bio-medicine or marketing. Similarity search in data with increasing dimensionality results in an exponential growth of the search space, referred to as Curse of Dimensionality. A common approach to postpone this effect(More)
In this work, we present a distributed caching solution which addresses the problem of efficient delivery of HTTP live streams in large private networks. With our system, we have conducted tests on a number of pilot deployments. The largest of them, with 3000 concurrent viewers, consistently showed that our system saves more than 90% of traffic towards the(More)
Distributed hash tables (DHT) often rely on uniform hashing for balancing the load among their nodes. However, the most overloaded node may still have a load up to O(log N) times higher than the average load. DHTs with support for range queries cannot rely on hashing to fairly balance the system's load since hashing destroys the order of the stored items.(More)
There are only few data mining algorithms that work in a massively parallel and yet online (i.e. incremental) fashion. A combination of both features is essential for mining of large data streams and adds scalability to the concept of Online Aggregation introduced by J. M. Hellerstein et al. in 1997. We show how an online version of the Map-Reduce(More)