Working Set
The subset of data and code actively needed during an execution interval, whose size strongly affects cache and memory behavior.
Performance Context
A working set is the subset of code and data actively needed during an execution interval. Once it exceeds a relevant cache or physical-memory capacity, cache misses, page faults, and storage access can increase sharply, changing the performance regime.
Measurement Boundary
The total data set and the working set are not the same. A very large database can have a small hot subset, so benchmark data size should represent the production access distribution rather than only total capacity.