On reconfiguring query execution plans in distributed object-relational DBMS

K. Ng, Zhenghao Wang, R. Muntz, E. C. Shek
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引用次数: 9

Abstract

Massive database sizes and growing demands for decision support and data mining result in long-running queries in extensible object-relational DBMSs, particularly in decision support and data warehousing analysis applications. Parallelization of query evaluation is often required for acceptable performance, yet queries are frequently processed suboptimally due to (1) only coarse or inaccurate estimates of the query characteristics and database statistics being available prior to query evaluation; (2) changes in system configuration and resource availability during query evaluation. In a distributed environment, dynamically reconfiguring query execution plans (QEPs), which adapts QEPs to the environment as well as to the query characteristics, is a promising means to significantly improve query evaluation performance. Based on an operator classification, we propose an algorithm to coordinate the steps in a reconfiguration and introduce alternatives for execution context checkpointing and restoring. A syntactic extension of SQL to expose the relevant characteristics of user-defined functions in support of dynamic reconfiguration is proposed. An example from the experimental system is presented.
分布式对象-关系DBMS中查询执行计划的重构研究
庞大的数据库规模以及对决策支持和数据挖掘日益增长的需求导致在可扩展的对象关系dbms中出现长时间运行的查询,特别是在决策支持和数据仓库分析应用程序中。为了获得可接受的性能,通常需要并行化查询评估,但是查询的处理经常不是最优的,这是因为:(1)在查询评估之前,只有对查询特征和数据库统计信息的粗略或不准确的估计;(2)查询评估过程中系统配置和资源可用性的变化。在分布式环境中,动态重新配置查询执行计划(qep),使qep适应环境和查询特征,是一种有希望显著提高查询评估性能的方法。基于算子分类,我们提出了一种算法来协调重新配置中的步骤,并引入了执行上下文检查点和恢复的替代方法。提出了一种SQL的语法扩展,以公开用户定义函数的相关特征,支持动态重新配置。给出了实验系统的一个实例。
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