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.