Browsing by Author "Jaewoo Kang, Committee Member"

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    Query Size Estimation through Sampling
    (2005-01-06) Kim, Kyoung-Hwa; Jaewoo Kang, Committee Member; Xiaosong Ma, Committee Member; Rada Y. Chirkova, Committee Chair
    Current Database management systems (DBMS) handle huge amounts of data and need fast query response time. DBMSs apply several strategies to execute user queries. Query optimizers in DBMSs compare costs for these strategies and choose the cheapest one. Materialized views are suggested to enhance query response time as one of the strategies in DBMSs. Cost of each strategy has to be accurately estimated to choose right strategy. Because the materialized view is stored as a one table, we consider that sequential scan is used for executing of the materialized view. Therefore, I/O and CPU costs to execute materialized views depend on the number of tuples for the result. Hence, Our focus will be the accuracy of estimation of the number of tuples in materialized views; that is a query-size estimation. Many researches have been proposed to find methods to estimate the cost of query. This thesis reviews these researches and compares good and bad aspects for each cost estimation method. We choose size estimation methods that are more accurate than others to implement. We suggest various query environments for experiments. We suggest a guideline by experimental results.
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    A Scalable Architecture for SIP using Content Addressable Networks
    (2005-06-07) Balasubramanian, Ramrajprabu; Jaewoo Kang, Committee Member; Khaled Harfoush, Committee Member; Injong Rhee, Committee Chair
    Session initiation protocol (SIP) provides call establishment functions for VoIP including location resolution, authentication, signaling compression, and billing. These functions, when combined with the text-based nature of the protocol, are highly CPU-intensive under a peak load. Practical limitation on the available CPU power of a single SIP server mandates that the SIP infrastructure supporting these functions be distributed over multiple servers. Existing approaches to this problem using multiple nodes for SIP processing with a shared location database or a replicated location database to distribute the load are unfortunately not scalable or fault-tolerant, incurring high maintenance and update overheads or introducing a single point of failure. This thesis presents a proof-of-concept design and analysis of a scalable, robust architecture for SIP infrastructures using a content addressable network (CAN) model, called CASIP (CAN-based SIP). The combination of CAN and SIP is highly complementary. The performance study of CASIP using an implementation using a real SIP stack and NS-2 simulations shows that the proposed system distributes the SIP processing (both location update and lookup) load of the network over multiple nodes very effectively without incurring much routing and maintenance overhead; with use of simple cache schemes, CASIP can linearly add the number of servers in proportion to the increase in the subscriber base. The study also indicates that CASIP keeps the reconfiguration overhead minimal. Furthermore, the CASIP architecture exhibits high availability: a CASIP network of 50 nodes recovers from a server crash within 5 minutes, during which only 2% of call setup requests are dropped. These features enable cost-effective, incremental deployment of SIP servers in response to the user population growth