Visualizing the robustness of query execution

TL;DR

This paper introduces visualization techniques to assess and compare the robustness of query execution plans under varying run-time conditions in database systems.

Contribution

It presents diagrams for visualizing plan performance and degradation, providing insights into system robustness during query execution.

Findings

Visual diagrams reveal how plans perform under adverse conditions

Different systems show varying robustness patterns

Visualization aids in identifying robustness weaknesses

Abstract

In database query processing, actual run-time conditions (e.g., actual selectivities and actual available memory) very often differ from compile-time expectations of run-time conditions (e.g., estimated predicate selectivities and anticipated memory availability). Robustness of query processing can be defined as the ability to handle unexpected conditions. Robustness of query execution, specifically, can be defined as the ability to process a specific plan efficiently in an unexpected condition. We focus on query execution (run-time), ignoring query optimization (compile-time), in order to complement existing research and to explore untapped potential for improved robustness in database query processing. One of our initial steps has been to devise diagrams or maps that show how well plans perform in the face of varying run-time conditions and how gracefully a system's query architecture, operators, and their implementation degrade in the face of adverse conditions. In this paper, we show several kinds of diagrams with data from three real systems and report on what we have learned both about these visualization techniques and about the three database systems