Browsing by Subject "Continuous queries"

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Open Access
Building user-defined runtime adaptation routines for stream processing applications
(VLDB Endowment, 2012) Jacques-Silva, G.; Gedik, B.; Wagle, R.; Wu, Kun-Lung; Kumar, V.
Stream processing applications are deployed as continuous queries that run from the time of their submission until their cancellation. This deployment mode limits developers who need their applications to perform runtime adaptation, such as algorithmic adjustments, incremental job deployment, and application-specific failure recovery. Currently, developers do runtime adaptation by using external scripts and/or by inserting operators into the stream processing graph that are unrelated to the data processing logic. In this paper, we describe a component called orchestrator that allows users to write routines for automatically adapting the application to runtime conditions. Developers build an orchestrator by registering and handling events as well as specifying actuations. Events can be generated due to changes in the system state (e.g., application component failures), built-in system metrics (e.g., throughput of a connection), or custom application metrics (e.g., quality score). Once the orchestrator receives an event, users can take adaptation actions by using the orchestrator actuation APIs. We demonstrate the use of the orchestrator in IBM's System S in the context of three different applications, illustrating application adaptation to changes on the incoming data distribution, to application failures, and on-demand dynamic composition. © 2012 VLDB Endowment.
Open Access
Processing of continuous queries from moving objects in mobile computing systems
(1999) Gök, Hüseyin Gökmen
Recent advances in computer hardware technology and wireless communication networks have led to the emergence of mobile computing systems. In a mobile computing environment, a user with a wireless connection to the information network can access data via submitting queries to the data server. Since the mobility is the most distinguishing feature of the mobile computing paradigm, location becomes an important piece of information for the so called location-dependent queries where the answer to a query depends on the current location of the user who issued the query. A location-dependent query submitted by a mobile user can become more difficult to process when it is submitted as a continuous query for which the answer changes as the user moves. The answer to a location-dependent continuous query is a set that consists of tuples < 5', begin, end > indicating that object S is the answer of the query from time begin to time end. Once the tuples in the answer set are determined, the next step is to determine when to send these tuples to the user. The transmission time of the tuples is critical in the sense that it can affect the communication overhead imposed on the wireless network and the availability of tuples in case of disconnections. In this thesis, we propose three tuple transmission approaches that determine the transmission time of a tuple in the answer set of a location-dependent continuous query. We also design and implement a simulation model to compare the performance of the proposed tuple transmission approaches under different settings of environmental parameters.