Optimizing Repetitive Computations of Database Triggers Within a Transaction

Projet RODINWe study the problem of optimizing costly repetitive evaluations of database triggers within a transaction. We first show that well known incremental rule evaluation algorithms such as RETE or TREAT are inappropriate for that because they do not consider how repetitive triggerings of rules can be caused by the structure of transaction programs. Therefore, their decision of precomputing and caching some expressions in rule conditions for a later reuse can be erroneous. We assume that transaction programs are represented by their flow graph. We then propose an algorithm that, given a transaction's flow graph, and a set of triggers, constructs a compact data structure called a triggering graph. First, for each possible transaction execution, this graph indicates which rules may be triggered. Second, for every rule $r$ capable of being triggered and fired several times, the graph represents the real «influence» of both the transaction and the rules on $r$. This provides the necessary information for deciding which subexpressions of $r$ are most profitable to cache for the considered transaction

Language for directed exploration and analysis of sequence data

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 81-84).This thesis describes a sequence-data processing toolkit for analysis of Intelligent Tutoring System (ITS) log data, that unlike other tools allows directed exploration of sequence patterns. This system provides a powerful yet straightforward abstraction for sequence-data processing, and a set of high-level manipulation primitives which allow arbitrarily complex transformations of such data. Using this language, very sophisticated queries can be performed using only a few lines of code. Furthermore, queries can be constructed interactively, allowing for rapid development, refinement, and comparison of hypotheses. Importantly, this system is not limited to ITS logs, but is equally applicable to the manipulation of any form of (potentially multidimensional) sequence data.by Eric J.P. Mumpower.M.Eng

Integración de mecanismos activos en un MBDOO

El objetivo del presente trabajo es mostrar los aspectos relevantes para extender la definición de SIGMA a un modelo de base de datos activo. En el capítulo uno se revisan los conceptos básicos sobre sistemas de bases de datos orientados a objetos, en el capítulo dos se describen las ventajas de contar con un DBMS que tenga capacidad para realizar el control automático de restricciones, justificando la necesidad de la incorporación de un sistema de reglas para tomarlo en un modelo activo. En los capítulos tres y cuatro se exponen los sistemas de reglas, sus principales características y funcionamiento, y las cuestiones que deben resolverse cuando se los incorpora en un DBMS. En el capítulo cinco se definen los aspectos fundamentales para incorporar un sistema de reglas en SIGMA. En el seis se hace un análisis de las propuestas existentes más difundidas sobre bases de datos activas, comparando sus principales características con las del capítulo cinco. Por último, en el séptimo, se realizan las conclusiones del trabajo.Tesis digitalizada en SEDICI gracias a la colaboración de la Biblioteca de la Facultad de Informática. En las últimas páginas se advierten borrones en el original que no pudieron ser mejorados con la digitalización.Facultad de Ciencias Exacta

Integración de mecanismos activos en un MBDOO

El objetivo del presente trabajo es mostrar los aspectos relevantes para extender la definición de SIGMA a un modelo de base de datos activo. En el capítulo uno se revisan los conceptos básicos sobre sistemas de bases de datos orientados a objetos, en el capítulo dos se describen las ventajas de contar con un DBMS que tenga capacidad para realizar el control automático de restricciones, justificando la necesidad de la incorporación de un sistema de reglas para tomarlo en un modelo activo. En los capítulos tres y cuatro se exponen los sistemas de reglas, sus principales características y funcionamiento, y las cuestiones que deben resolverse cuando se los incorpora en un DBMS. En el capítulo cinco se definen los aspectos fundamentales para incorporar un sistema de reglas en SIGMA. En el seis se hace un análisis de las propuestas existentes más difundidas sobre bases de datos activas, comparando sus principales características con las del capítulo cinco. Por último, en el séptimo, se realizan las conclusiones del trabajo.Tesis digitalizada en SEDICI gracias a la colaboración de la Biblioteca de la Facultad de Informática. En las últimas páginas se advierten borrones en el original que no pudieron ser mejorados con la digitalización.Facultad de Ciencias Exacta

Rule Condition Testing and Action Execution in Ariel

This paper describes testing of rule conditions and execution of rule actions in the Ariel active DBMS. The Ariel rule system is tightly coupled with query and update processing. Ariel rules can have conditions based on a mix of patterns, events, and transitions. For testing rule conditions, Ariel makes use of a discrimination network composed of a special data structure for testing single-relation selection conditions efficiently, and a modified version of the TREAT algorithm, called A-TREAT, for testing join conditions. The key modification to TREAT (which could also be used in the Rete algorithm) is the use of virtual ff-memory nodes which save storage since they contain only the predicate associated with the memory node instead of copies of data matching the predicate. The rule-action executor in Ariel binds the data matching a rule's condition to the action of the rule at rule fire time, and executes the rule action using the query processor. 1 Introduction Designers of database..

Fault-tolerance and load management in a distributed stream processing system

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 187-199).Advances in monitoring technology (e.g., sensors) and an increased demand for online information processing have given rise to a new class of applications that require continuous, low-latency processing of large-volume data streams. These "stream processing applications" arise in many areas such as sensor-based environment monitoring, financial services, network monitoring, and military applications. Because traditional database management systems are ill-suited for high-volume, low-latency stream processing, new systems, called stream processing engines (SPEs), have been developed. Furthermore, because stream processing applications are inherently distributed, and because distribution can improve performance and scalability, researchers have also proposed and developed distributed SPEs. In this dissertation, we address two challenges faced by a distributed SPE: (1) faulttolerant operation in the face of node failures, network failures, and network partitions, and (2) federated load management. For fault-tolerance, we present a replication-based scheme, called Delay, Process, and Correct (DPC), that masks most node and network failures.(cont.) When network partitions occur, DPC addresses the traditional availability-consistency trade-off by maintaining, when possible, a desired availability specified by the application or user, but eventually also delivering the correct results. While maintaining the desired availability bounds, DPC also strives to minimize the number of inaccurate results that must later be corrected. In contrast to previous proposals for fault tolerance in SPEs, DPC simultaneously supports a variety of applications that differ in their preferred trade-off between availability and consistency. For load management, we present a Bounded-Price Mechanism (BPM) that enables autonomous participants to collaboratively handle their load without individually owning the resources necessary for peak operation. BPM is based on contracts that participants negotiate offline. At runtime, participants move load only to partners with whom they have a contract and pay each other the contracted price. We show that BPM provides incentives that foster participation and leads to good system-wide load distribution. In contrast to earlier proposals based on computational economies, BPM is lightweight, enables participants to develop and exploit preferential relationships, and provides stability and predictability.(cont.) Although motivated by stream processing, BPM is general and can be applied to any federated system. We have implemented both schemes in the Borealis distributed stream processing engine. They will be available with the next release of the system.by Magdalena Balazinska.Ph.D