Travel light:State shedding for efficient operator migration

Operator migration is a crucial concept to adapt event processing systems to dynamic changes. When the placement of a stateful operator changes, the operator state must be migrated to the new host. However, operator state size and time constraints can make it impossible to migrate the operator without severe Quality of Service (QoS) degradation. As a relief, we propose to perform state shedding in such a situation. The core idea of state shedding is to partition the operator state, assign a utility to each partial state, and use the utility and size of each partial state to identify the most useful partial states that can be migrated in a given time frame. Thus, state shedding can maintain a substantially higher QoS with a lower impact on query results than state-of-the-art solutions targeting consistent state at the old and new host. In this paper, we define this novel approach and in a simulation environment evaluate state shedding in migration scenarios with pattern-matching queries

Communication software model of WSN device for more accurate simulation in ns-3

Emerging infrastructure-less network architectures such as WSNs consist of devices that perform packet processing in software. General-purpose network simulators do currently not possess models to simulate the intra-node delay of such devices. Consider a real TelosB mote that runs TinyOS which spends seven and fifteen ms on processing packets of size 36 and 124 bytes. Failing to simulate that results in inaccurate simulation of packet loss, jitter, and latency. In this thesis, we create a communication software model of TelosB to include its temporal behavior for more accurate WSN simulations in the ns-3 simulator. A challenge in doing so is to create a tracing framework for TinyOS that can be used to accurately and reliably trace its behavior. The evaluation of the model shows that it is accurate, scalable, and has a significant impact when including it in a simulation