Reference Counting vs. Tracing GC

There are only two ways to decide an object is dead: count how many references point to it, or trace from the roots and see what's still reachable. This video puts reference counting and tracing side by side — the per-object counter decrement versus the mark phase, ARC versus a stop-the-world pause — and shows why the industry keeps switching between them.

Topics covered:

• Reference counting: increment on retain, decrement on release
• The cycle problem: why refcounting alone leaks self-referencing structures
• ARC: compile-time retain/release insertion and its overhead
• Tracing GC: the root set, the mark phase, and reachability as the definition of alive
• The pause: why tracing collects in batches and refcounting frees instantly
• Swift and Rust's choices: ownership moves vs. runtime counters
• Hybrids: Python's refcount plus a cycle detector
• The real trade-off: latency spikes vs. per-operation overhead and memory footprint