Node memory management

Node is built on the V8 engine, and uses the same memory management as that.

V8 uses a generational garbage collector, which is based on the generational hypothesis.

The generational hypothesis states:

In most cases, young objects are much more likely to die than old objects.

Or, most objects are short-lived. For example, a short-lived object might be the body of an API response. A long-lived object may be a static config or some singleton. There are many API responses, but only one config.

V8 splits its heap memory into two spaces, one New Space (or semi-space in command-line arguments) for short-lived objects, and an Old Space, where long-lived objects are promoted to.

By default, V8 will determine how often to run its garbage collection, but this can be tuned.

See Understanding and Tuning Memory from the Node documentation

Tuning and diagnosing memory usage

You can tune Node's garbage collection using CLI flags, for example:

node
    # Set Old Space size to 4096MB
    --max-old-space-size=4096
    # Set New Space size to 64MB
    --max-semi-space-size=64
    # Manually set the interval the GC runs to 100ms
    --gc-interval=100
    # Allow usage of `global.gc()` to trigger GCs
    --expose-gc
    index.js

When --expose-gc is set, you can manually trigger a garbage collection like:

someMemoryIntensiveProcess();

// Trigger collection
global.gc();

You can monitor memory usage in a running Node process like:

// process.memoryUsage() returns an object
console.log(process.memoryUsage());