Publish/subscribe (pub/sub) infrastructures running as a service on cloud environments offer simplicity and flexibility for composing distributed applications. Provisioning them appropriately is however challenging. The amount of stored subscriptions and incoming publications varies over time, and the computational cost depends on the nature of the applications and in particular on the filtering operation they require (e.g., content-based vs. topic-based, encrypted vs. non-encrypted filtering). The ability to elastically adapt the amount of resources required to sustain given throughput and delay requirements is key to achieving cost-effectiveness for a pub/sub service running in a cloud environment. In this paper, we present the design and evaluation of an elastic contentbased pub/sub system: E-STREAMHUB. Specific contributions of this paper include: (1) a mechanism for dynamic scaling, both out and in, of stateful and stateless pub/sub operators, (2) a local and global elasticity policy enforcer maintaining high system utilization and stable end-to-end latencies, and (3) an evaluation using real-world tick workload from the Frankfurt Stock Exchange and encrypted content-based filtering.
MapReduce has become a popular programming paradigm in the domain of batch processing systems. Its simplicity allows applications to be highly scalable and to be easily deployed on large clusters. More recently, the MapReduce approach has been also applied to Event Stream Processing (ESP) systems. This approach, which we call StreamMapReduce, enabled many novel applications that require both scalability and low latency.Another recent trend is to move distributed applications to public clouds such as Amazon EC2 rather than running and maintaining private data centers. Most cloud providers charge their customers on an hourly basis rather than on CPU cycles consumed. However, many applications, especially those that process online data, need to limit their CPU utilization to conservative levels (often as low as 50%) to be able to accommodate natural and sudden load variations without causing unacceptable deterioration in responsiveness.In this paper, we present a new fault tolerance approach based on active replication for StreamMapReduce systems. This approach is cost effective for cloud consumers as well as cloud providers. Cost effectiveness is achieved by fully utilizing the acquired computational resources without performance degradation and by reducing the need for additional nodes dedicated to fault tolerance.
This paper describes an extremely facile method to fabricate metallic wires at room temperature. The wires form by stretching viscoelastic polymer substrates supporting a drop of gallium-based liquid metal. Stretching the polymer causes the metal to also elongate due to the adhesion between the two materials. The diameters of the resulting wires, which can be as small as 10 m, decrease with increasing strain. This method is inspired by the process used for drawing optical fibers, which involves pulling a pre-form cylinder of molten glass until it thins to the size of a fiber. In contrast, the process here is done at room temperature and realized without the need for large forces. Moreover, geometries beyond simple wires are possible including parallel, core-shell, branched, and helix structures. The resulting wires can be elastic (stretchable), viscoelastic (soft), or plastic (stiff) depending on the chemistry and post-processing of the polymer. Wires can make electrical contacts by allowing the metal to sink through the viscoelastic polymer onto a substrate containing electrodes. In addition, removing the polymer substrate after elongation produces freestanding liquid metal wires stabilized by the surface oxide on the metal. Rheological studies show that polymers with a variety of properties can be utilized to form these wires including viscoelastic materials and gels. The ability to form metallic wires in a simple manner may find uses in soft and stretchable electronics, or enable new applications, such as 'wires on demand' for repairing electrical connections.
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