Mounir Tlili

P2P logging and timestamping for reconciliation

In this paper, we address data reconciliation in peer-to-peer (P2P) collaborative applications. We propose P2P-LTR (Logging and Timestamping for Reconciliation) which provides P2P logging and timestamping services for P2P reconciliation over a distributed hash table (DHT). While updating at collaborating peers, updates are timestamped and stored in a highly available P2P log. During reconciliation, these updates are retrieved in total order to enforce eventual consistency. In this paper, we first give an overview of P2P-LTR with its model and its main procedures. We then present our prototype used to validate P2P-LTR. To demonstrate P2P-LTR, we propose several scenarios that test our solutions and measure performance. In particular, we demonstrate how P2P-LTR handles the dynamic behavior of peers with respect to the DHT.

XWiki Concerto: A P2P Wiki System Supporting Disconnected Work

This paper presents the XWiki Concerto system, the P2P version of the XWiki server. This system is based on replicating wiki pages on a network of wiki servers. The approach, based on the Woot algorithm, has been designed to be scalable, to support the dynamic aspect of P2P networks and network partitions. These characteristics make our system capable of supporting disconnected edition and sub-groups, making it very flexible and usable.

Continuous timestamping for efficient replication management in DHTs

Distributed Hash Tables (DHTs) provide an efficient solution for data location and lookup in large-scale P2P systems. However, it is up to the applications to deal with the availability of the data they store in the DHT, e.g. via replication. To improve data availability, most DHT applications rely on data replication. However, efficient replication management is quite challenging, in particular because of concurrent and missed updates. In this paper, we propose an efficient solution to data replication in DHTs. We propose a new service, called Continuous Timestamp based Replication Management (CTRM), which deals with the efficient storage, retrieval and updating of replicas in DHTs. To perform updates on replicas, we propose a new protocol that stamps update actions with timestamps generated in a distributed fashion. Timestamps are not only monotonically increasing but also continuous, i.e. without gap. The property of monotonically increasing allows applications to determine a total order on updates. The other property, i.e. continuity, enables applications to deal with missed updates. We evaluated the performance of our solution through simulation and experimentation. The results show its effectiveness for replication management in DHTs.

Scalable P2P Reconciliation Infrastructure for Collaborative Text Editing

We address the problem of optimistic replication forcollaborative text editing in Peer-to-Peer (P2P) systems. This problem is challenging because of concurrent updating at multiple peers and dynamic behavior of peers. Operationaltransformation (OT) is a typical approach used for handlingoptimistic replication in the context of distributed text editing. However, most of OT solutions are neither scalable nor suited for P2P networks due to the dynamic behavior of peers. In this paper, we propose a scalable P2P reconciliation infrastructure for OT that assures eventual consistency and liveness despite dynamicity and failures. We propose a P2P logging and timestamping service called P2P-LTR (P2P Logging and Timestamping for Reconciliation) which exploits a distributed hash table (DHT) for reconciliation. While updating replica copies at collaborating peer editors, updates are stored in ahighly available P2P log. To enforce eventual consistency, these updates must be retrieved in a specific total order to be reconciled at the peer editors. P2P-LTR provides an efficient mechanism for determining the total order of updates. It also deals with the case of peers that may join and leave the system during the update operation. We evaluated the performance of P2P-LTR through simulation; the results show the efficiency and the scalability of our solution.

Replication in DHTs using dynamic groups

Distributed Hash Tables (DHTs) provide an efficient solution for data location and lookup in large-scale P2P systems. However, it is up to the applications to deal with the availability of the data they store in the DHT, e.g. via replication. To improve data availability, most DHT applications rely on data replication. However, efficient replication management is quite challenging, in particular because of concurrent and missed updates. In this paper, we propose a complete solution to data replication in DHTs. We propose a new service, called Continuous Timestamp based Replication Management (CTRM), which deals with the efficient storage, retrieval and updating of replicas in DHTs. In CTRM, the replicas are maintained by groups of peers which are determined dynamically using a hash function. To perform updates on replicas, we propose a new protocol that stamps the updates with timestamps that are generated in a distributed fashion using the dynamic groups. Timestamps are not only monotonically increasing but also continuous, i.e. without gap. The property of monotonically increasing allows applications to determine a total order on updates. The other property, i.e. continuity, enables applications to deal with missed updates. We evaluated the performance of our solution through simulation and experimentation. The results show its effectiveness for replication management in DHTs.

XWiki concerto: a P2P wiki for nomadic workers

XWiki Concerto is a research project aiming at evolving the open-source XWiki engine toward a P2P architecture supporting mobility, offline work and replication of content across a large number of peers. This research brings XWiki the capacity to (i) run on a fault tolerant P2P architecture allowing to scale to millions of users using a secure solution supporting replication and synchronization of contents, (ii) support mobile workers in their daily collaborative activities. This paper presents the research challenges of the project and the algorithms that have been designed for collaborative P2P editing. XWiki Concerto brings together XWiki, INRIA, ENST, EISTI, and Mandriva and is sponsored by the French Research Agency. The XWiki Concerto components will be released as LGPL software.

XWiki concerto: un wiki sur réseau P2P supportant le nomadisme

This paper describes the demonstration of the XWiki Concerto system. XWiki Concerto is a a P2P wiki that supports mobile users. Each XWiki server is the network is extended with a replication manager that propagates local changes to remote servers and merges concurrent changes. The demonstration is based on a scenario in which different servers are used to concurrently edit a wiki page. One of the servers is then disconnected from the network but continue to be used to edit the page. The different copies are then reconciliated when the server is re- conected.

P2P logging and timestamping for XWiki

Collaborative applications are getting an increasing interest as a result of the rapid progress in distributed technologies such as grid computing. P2P applications, and mobile computing. Constructing these applications on top of P2P networks has many advantages which stem from P2P properties: decentralization, self-organization, scalability and fault-tolerance In this paper, we address data replication and reconciliation in XWiki peer-to-peer (P2P) collaborative application. We propose a new mechanism of optimistic replication, which consists of an algorithm for data reconciliation based on operational transformation approach (OT) and an extension of KTS service that performs distributed timestamp generation running over a distributed hash table (DHT). While updating at collaborating XWiki peers, updates are timestamped and stored in a highly available P2P log. During reconciliation, these updates are retrieved in total order to enforce eventual consistencies. The work presented here is partially supported by the National Agency of Research within RNTL XWiki Concerto project (2007--2009).