V8 Garbage Collection Mechanisms: Orinoco and Beyond

The Generational Hypothesis

Modern memory management inside the V8 JavaScript engine is predicated on a crucial empirical observation: most allocated objects die incredibly young. Temporal variables used in loops or immediate DOM calculations become obsolete almost instantly. Conversely, objects that survive the initial allocation phase tend to live for the entire lifecycle of the application context.

The Scavenger and the Old Space

V8 divides its memory heap primarily into the 'New Space' (nursery) and the 'Old Space'. Memory allocations begin in the New Space. A rapid, lightweight algorithm called the 'Scavenger' regularly sweeps this tiny area, completely discarding unreferenced objects. It operates using a Cheney algorithm, copying only the surviving objects between semi-spaces. If an object survives two scavenger cycles, V8 formally evicts it and promotes it to the Old Space.

Mark-Sweep and Concurrent Tracing

The Old Space requires a far heavier 'Mark-and-Sweep' or 'Mark-and-Compact' paradigm. Historically, analyzing thousands of long-lived objects forced V8 to drastically pause the main thread—creating visually stuttering 'Stop-The-World' jank in web pages. Modern V8 iterations (project Orinoco) have heavily parallelized this garbage collection. Using concurrent marking, background worker threads trace obsolete memory while the main JavaScript thread continues execution undisturbed, achieving sub-millisecond GC latency.