  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
