When investigating memory usage, what is the most important measurement for capacity planning purposes?

Resident Set Size (RSS) directly measures the amount of physical RAM (main memory) currently occupied by a process, excluding swapped-out pages and shared library code that hasn't been loaded. This metric is crucial for capacity planning because it accurately reflects the process's demand on physical memory resources, which directly impacts system performance and overall memory availability.

Total memory refers to the total physical RAM installed on the system, which is a system-level metric, not a process-specific usage.

Virtual Memory Size (VSZ) includes all memory that a process can access, including physical RAM, swapped-out memory, and memory mapped from files and libraries. It often overstates actual physical memory usage and is less indicative of physical RAM pressure.

Swap memory usage indicates how much data has been moved from RAM to disk, which is a symptom of physical memory pressure rather than a direct measure of a process's current physical memory consumption for capacity planning.