TrackingVariable

TrackingVariable is a software design concept describing a variable whose changing values are recorded over time. Unlike ordinary variables that hold only a single value, a TrackingVariable preserves a history of past values along with metadata such as when the change occurred and why it happened. The history enables auditing, debugging, and time-based analyses.

A TrackingVariable typically consists of at least a value field and a change history. Each update appends a new record with timestamp, new value, and optional metadata like source, change_reason, user_id, or context. Some implementations support efficient storage via deltas or snapshots and provide APIs to retrieve the current value, a range of historical values, or roll back to a previous state. In reactive or event-driven systems, tracking variables may emit change events to observers.

Applications: tracking variables are used in debugging to observe state evolution, in simulations to record the evolution of state over time, in telemetry and analytics to correlate metrics with events, and in experiments to compare control and treatment groups over time.

Considerations: storing history incurs memory and I/O overhead and may raise privacy or security concerns if sensitive data is captured. Design choices include how long to retain history, how to compress data, and how to thread-safely update in concurrent environments. See also: audit log, time-series data, versioning, observables.