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- pDomus: a prototype for cluster-oriented distributed hash tablesPublication . Rufino, José; Pina, António; Alves, Albano; Exposto, JoséThe Domus architecture for distributed hash tables (DHTs) is specially designed to support the concurrent deployment of multiple and heterogeneous DHTs, in a dynamic shared-all cluster environment. The execution model is compatible with the simultaneous access of several distributed/parallel client applications to the same or different running DHTs. Support to distributed routing and storage is dynamically configurable per node, as a function of applications requirements, node base resources and the overall cluster communication, memory and storage usage. pDomus is a prototype of Domus that creates an environment where to evaluate the model embedded concepts and planned features. In this paper, we present a series of experiments conduced to obtain figures of merit i) for the performance of basic dictionary operations, and ii) for the storage overhead resulting from several storage technologies. We also formulate a ranking formula that takes into account access patterns of clients to DHTs, to objectively select the most adequate storage technology, as a valuable metric for a wide range of application scenarios. Finally, we also evaluate client applications and services scalability, for a select dictionary operation. Results of the overall evaluation are promising and a motivation for further work
- A cluster oriented model for dynamically balanced DHTsPublication . Rufino, José; Pina, António; Alves, Albano; Exposto, JoséIn this paper, we refine previous work on a model for a Distributed Hash Table (DHT) with support to dynamic balancement across a set of heterogeneous cluster nodes. We present new high-level entities, invariants and algorithms developed to increase the level of parallelism and globally reduce memory utilization. In opposition to a global distribution mechanism, that relies on complete knowledge about the current distribution of the hash table, we adopt a local approach, based on the division of the DHT into separated regions, that possess only partial knowledge of the global hash table. Simulation results confirm the hypothesis that the increasing of parallelism has as counterpart the degradation of the quality of the balancement achieved with the global approach. However, when compared with Consistent Hashing and our global approach, the same results clarify the relative merits of the extension, showing that, when properly parameterized, the model is still competitive, both in terms of the quality of the distribution and scalability.
- Distributed paged Hash tablesPublication . Rufino, José; Pina, António; Alves, Albano; Exposto, JoséIn this paper we present the design and implementation of DPH, a storage layer for cluster environments. DPH is a Distributed Data Structure (DDS) based on the distribution of a paged hash table. It combines main memory with file system resources across the cluster in order to implement a distributed dictionary that can be used for the storage of very large data sets with key based addressing techniques. The DPH storage layer is supported by a collection of cluster-aware utilities and services. Access to the DPH interface is provided by a user-level API. A preliminary performance evaluation shows promising results.
- Domus - an architecture for cluster-oriented distributed Hash tablesPublication . Rufino, José; Pina, António; Alves, Albano; Exposto, JoséThis paper presents a high level description of Domus, an architecture for cluster-oriented Distributed hash Tables. As a data management layer, Domus supports the concurrent execution of multiple and heterogeneous DHTs, that may be simultaneously accessed by different distributed/parallel client applications. At system level, a load balancement mechanism allows for the (re)distribution of each DHT over cluster nodes, based on the monitoring of their resources, including CPUs, memory, storage and network. Two basic units of balancement are supported: vnodes, a coarse-grain unit, and partitions, a fine-grain unit. The design also takes advantage of the strict separation of object lookup and storage, at each cluster node, and for each DHT. Lookup follows a distributed strategy that benefits from the joint analysis of multiple partition-specific routing information, to shorten routing paths. Storage is accomplished through different kinds of data repositories, according to the specificity and requirements of each DHT.
- Toward a dynamically balanced cluster oriented DHTPublication . Rufino, José; Pina, António; Alves, Albano; Exposto, JoséIn this paper, we present a model for a cluster oriented Distributed Hash Table (DHT). It introduces software nodes, virtual nodes and partitions as high level entities that, in conjunction with the definition of a certain number of in variants, provide for the balancement of a DHT across a set of heterogeneous cluster nodes. The model has the following major features: a) the share of the hash table handled by each cluster node is a function of its enrollment level in the DHT; b) the enrollment level of a cluster node in the DHT may change dynamically; c) cluster nodes are allowed to dynamically join or leave the DHT. A preliminary evaluation proved that the quality of the balancement of partitions of the hash table across the cluster, measured by the stan dard deviation with relation to the ideal average, surpass the one achieved by using another well known approach.
- Shortcut routing for chord graphs in the domus hash spacePublication . Rufino, José; Pina, António; Alves, Albano; Exposto, JoséWe present and evaluate shortcut routing algorithms for Chord graphs in the hash space, specifically developed to accelerate distributed lookups in the Distributed Hash Tables (DHTs) of the Domus framework. The algorithms explore our findings about the relation of exponential and euclidean distances in Chord graphs, in conjunction with the availability, in each DHT node, of multiple routing tables of the underlying Chord graph. The outcome are routing decisions capable of achieving average distances as low as 40% of those offered by Chord’s conventional routing method. Moreover, the supplemental computational effort to take the shortcut routing decisions is sufficiently low to make the algorithms useful in a broad set of application scenarios.