Ferrero-Baker, Osvaldo

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    A crash and resume query mechanism for the nettraveler database middleware system
    (2009) Ferrero-Baker, Osvaldo; Rodríguez-Martínez, Manuel; College of Engineering; Vélez-Rivera, Bienvenido; Rivera-Vega, Pedro I.; Department of Electrical and Computer Engineering; Ferrer-Alameda, Mercedes
    The need of ubiquitous data access is quickly emerging in our everyday life. The devices that we would like to access are usually heterogeneous. These heterogeneous devices may contain their own set of protocols and instructions. Database middleware systems are used in order to mask the heterogeneity of devices. Such devices may be enterprise servers or full fledged machines, with constant power and connectivity to devices with limited connectivity, low power and/or other limitations. Database middleware systems take this heterogeneity into consideration and allow users to access these devices through a common interface. In most database middleware systems its components are assumed to have constant power and or network connectivity. For this reason, crashes of such components are not expected to occur and if they did the query work would need to be restarted. However, when integrating mobile devices such as PDA’s, laptops, cell phones, etc. with database middleware systems, additional procedures or protocols may be required in order to maintain an acceptable query throughput. This thesis work deals with one of these protocols designed in order to aid mobile devices. Specifically with the issue of a crash or disconnection of any of the components involved during query execution, where crashes may occur frequently. We believe that the execution time for queries can be decreased by using a crash and resume mechanism in order to resume query execution from the point the crash occurred. With the creation of this mechanism, the recovery of query work in the case of a crash, network failure or component unavailability is now possible. This mechanism would allow mobile devices with a more robust participation as service providers in a database middleware system. The mechanism was implemented over the NetTraveler database middleware system as part of this thesis work. The implementation was used in order to carry out experiments that would show the benefits and help identify the limitations of this crash and resume mechanism. The experiments showed that as the crash occurs at a later point of query execution the use of the crash and resume mechanism becomes more viable. It also showed that as the size of the query’s result set increases so does the gains obtained if a crash occurred.