| 1. |
- Shafaat, Tallat M., et al.
(författare)
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On consistency of data in structured overlay networks
- 2008
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Ingår i: GRID COMPUTING. - NEW YORK : SPRINGER. - 9780387094564 ; , s. 249-260
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Konferensbidrag (refereegranskat)abstract
- Data consistency can be violated in Distributed Hash Tables (DHTs) due to inconsistent lookups. In this paper, we identify the events leading to inconsistent lookups and inconsistent responsibilities for a key. We find the inaccuracy of failure detectors as the main reason for inconsistencies. By simulations with inaccurate failure detectors, we study the probability of reaching a system configuration which may lead to inconsistent data. We analyze majority-based algorithms for operations on replicated data. To ensure that concurrent operations do not violate consistency, they have to use non-disjoint sets of replicas. We analytically derive the probability of concurrent operations including disjoint replica sets. By combining the simulation and analytical results, we show that the probability for a violation of data consistency is negligibly low for majority-based algorithms in DHTs.
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| 2. |
- Trunfio, Paolo, et al.
(författare)
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Implementing dynamic querying search in k-ary DHT-based overlays
- 2008
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Ingår i: Grid Computing: Achievements and Prospects. - USA : Springer. - 9780387094564 ; , s. 275-286
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Bokkapitel (refereegranskat)abstract
- Distributed Hash Tables (DHTs) provide scalable mechanisms for implementing resource discovery services in structured Peer-to-Peer (P2P) networks. However, DHT-based lookups do not support some types of queries which are fundamental in several classes of applications. A way to support arbitrary queries in structured P2P networks is implementing unstructured search techniques on top of DHT-based overlays. This approach has been exploited in the design of DQDHT, a P2P search algorithm that combines the dynamic querying (DQ) technique used in unstructured networks with an algorithm for efficient broadcast over a DHT. Similarly to DQ, DQ-DHT dynamically adapts the search extent on the basis of the desired number of results and the popularity of the resource to be found. Differently from DQ, DQ-DHT exploits the structural constraints of the DHT to avoid message duplications. The original DQ-DHT algorithm has been implemented using Chord as basic overlay. In this paper we focus on extending DQ-DHT to work in k-ary DHT-based overlays. In a k-ary DHT, broadcast takes only O(logkN) hops using O(logkN) pointers per node. We exploit this “k-ary principle” in DQ-DHT to improve the search time with respect to the original Chord-based implementation. This paper describes the implementation of DQ-DHT over a k-ary DHT and analyzes its performance in terms of search time and generated number of messages in different configuration scenarios.
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