Matteo Migliavacca

Distributed complex event processing with query rewriting

The nature of data in enterprises and on the Internet is changing. Data used to be stored in a database first and queried later. Today timely processing of new data, represented as events, is increasingly valuable. In many domains, complex event processing (CEP) systems detect patterns of events for decision making. Examples include processing of environmental sensor data, trades in financial markets and RSS web feeds. Unlike conventional database systems, most current CEP systems pay little attention to query optimisation. They do not rewrite queries to more efficient representations or make decisions about operator distribution, limiting their overall scalability. This paper describes the NEXT CEP system that was especially designed for query rewriting and distribution. Event patterns are specified in a high-level query language and, before being translated into event automata, are rewritten in a more efficient form. Automata are then distributed across a cluster of machines for detection scalability. We present algorithms for query rewriting and distributed placement. Our experiments on the Emulab test-bed show a significant improvement in system scalability due to rewriting and distribution.

Towards lightweight information dissemination in inter-vehicular networks

Vehicular ad hoc networks have recently been proposed as an effective tool for improving both road safety and the comfort experienced while driving. Vehicles may propagate information about potentially dangerous events such as lane changes or sudden slowdowns to vehicles in their vicinity. Moreover they can inform vehicles approaching from farther areas about accidents and possible traffic jams. In both cases, data must be routed to specific areas, along paths determined by the underlying road traffic conditions.In this paper we propose a novel approach to address this routing problem. First, we define a message propagation function that encodes information about both target areas and preferred routes. Second, we show how this function can be exploited in several routing protocols; and finally, we evaluate the effectiveness of our approach by means of simulation. Results highlight the good performance of our routing approach in sparse as well as in dense networks.

Epidemic algorithms for reliable content-based publish-subscribe: an evaluation

Distributed content-based publish-subscribe middleware is emerging as a promising answer to the demands of modern distributed computing. Nevertheless, currently available systems usually do not provide reliability guarantees. This hampers their use in dynamic and unreliable scenarios, notably including mobile ones. We evaluate the effectiveness of an approach based on epidemic algorithms. Three algorithms we originally proposed in [P. Costa et al., (2003)] are thoroughly compared and evaluated through simulation in challenging unreliable settings. The results show that our use of epidemic algorithms improves significantly event delivery, is scalable, and introduces only limited overhead.

Structure-less content-based routing in mobile ad hoc networks

The decoupling and asynchrony properties of the content-based publish-subscribe paradigm makes it very appealing for dynamic wireless networks, like those that often occur in pervasive computing scenarios. Unfortunately, none of the currently available content-based publish-subscribe middleware fit the requirements of such extreme scenarios in which the network is subject to very frequent topological reconfigurations due to the mobility of nodes. In this paper we propose a protocol for content-based message dissemination tailored to mobile ad hoc networks (MANETs) with frequent topological changes. Message routing occurs without the support of any network-wide dispatching infrastructure thus eliminating the issue of maintaining such logical topology on top of a time varying physical topology. The paper reports an extensive simulation study, which provides numerical evidence of the effectiveness of the approach.

Introducing reliability in content-based publish-subscribe through epidemic algorithms

Distributed content-based publish-subscribe middleware provides the necessary decoupling, flexibility, expressiveness, and scalability required by modern distributed applications. Unfortunately, this middleware usually does not provide reliability, especially in the presence of highly reconfigurable scenarios. Indeed, this problem has been thus far largely disregarded by the research community and solutions developed in other contexts are not immediately applicable.In this paper, we tackle the problem of introducing reliability in content-based publish-subscribe in dynamic environments by exploiting epidemic algorithms, whose characteristics in terms of decentralization, scalability, and resilience to topological changes resonate with our problem.

A Context and Content-Based Routing Protocol for Mobile Sensor Networks

The need of monitoring people, animals, and things in general, brings to consider mobile WSNs besides traditional, fixed ones. Moreover, several advanced scenarios, like those including actuators, involve multiple sinks . Mobility and multiple sinks radically changes the way routing is performed, while the peculiarities of WSNs make it difficult to reuse protocols designed for other types of mobile networks. In this paper, we describe CCBR, a Context and Content-Based Routing protocol explicitly designed for multi-sink, mobile WSNs. CCBR adopts content-based addressing to effectively support the data-centric communication paradigm usually adopted by WSN applications. It also takes into account the characteristics (i.e., context) of the sensors to filter data. Simulations show that CCBR outperforms alternative approaches in the multi-sink, mobile scenarios it was designed for, while providing good performance in more traditional (fixed) scenarios.

Context-aware publish-subscribe: Model, implementation, and evaluation

Complex communication patterns often need to take into account the situation in which the information to be communicated is produced or consumed. Publish-subscribe, and particularly its content-based incarnation, is often used to convey this information by encoding the “context” of the publisher into the published messages. In this paper we claim that this approach is limiting and inefficient and propose a context-aware publish-subscribe model of communication as a better alternative. We describe a protocol that implements such model in a distributed publish-subscribe middleware, and analyze how it performs w.r.t. traditional content-based routing.

Content-Based Routing in Highly Dynamic Mobile Ad Hoc Networks

The decoupling and asynchrony properties of the content‐based publish‐subscribe paradigm makes it very appealing for dynamic wireless networks, like those that often occur in pervasive computing scenarios. Unfortunately, most of the currently available content‐based publish‐subscribe middleware do not fit the requirements of such extreme scenarios, in which the network is subject to very frequent topological reconfigurations due to mobility of nodes. In this paper we propose a protocol for content‐based message dissemination tailored to Mobile Ad Hoc Networks (MANETs) showing frequent topological changes. Message routing occurs without the support of any network‐wide dispatching infrastructure thus eliminating the need of maintaining such infrastructure on top of a physical network continuously changing its topology. The paper reports an extensive simulation study that confirms the suitability of the proposed approach along with a stochastic analysis of the central mechanism adopted by the protocol.

Enforcing End-to-End Application Security in the Cloud

Security engineering must be integrated with all stages of application specification and development to be effective. Doing this properly is increasingly critical as organisations rush to offload their software services to cloud providers. Service-level agreements (SLAs) with these providers currently focus on performance-oriented parameters, which runs the risk of exacerbating an impedance mismatch with the security middleware. Not only do we want cloud providers to isolate each of their clients from others, we also want to have means to isolate components and users within each client’s application.

NetAgg: Using Middleboxes for Application-specific On-path Aggregation in Data Centres

Data centre applications for batch processing (e.g. map/reduce frameworks) and online services (e.g. search engines) scale by distributing data and computation across many servers. They typically follow a partition/aggregation pattern: tasks are first partitioned across servers that process data locally, and then those partial results are aggregated. This data aggregation step, however, shifts the performance bottleneck to the network, which typically struggles to support many-to-few, high-bandwidth traffic between servers. Instead of performing data aggregation at edge servers, we show that it can be done more efficiently along network paths. We describe NETAGG, a software platform that supports on-path aggregation for network-bound partition/aggregation applications. NETAGG exploits a middlebox-like design, in which dedicated servers (agg boxes) are connected by high-bandwidth links to network switches. Agg boxes execute aggregation functions provided by applications, which alleviates network hotspots because only a fraction of the incoming traffic is forwarded at each hop. NETAGG requires only minimal application changes: it uses shim layers on edge servers to redirect application traffic transparently to the agg boxes. Our experimental results show that NETAGG improves substantially the throughput of two sample applications, the Solr distributed search engine and the Hadoop batch processing framework. Its design allows for incremental deployment in existing data centres and incurs only a modest investment cost.