process.memoryUsage() in Node

Node's global object process has a really cool helper function called memoryUsage() that helps measure (you guessed it) memory usage.

Some of the below code is taken and modified from Valentino Gagliardi's blog article on inspecting memory usage in Node.js.

const MB_DIVISOR = 1_000_000

const memoryUsage = process.memoryUsage()

console.log('memoryUsage', memoryUsage)

for (const [key, value] of Object.entries(memoryUsage))
  console.log(`${key} ${value / MB_DIVISOR}mb`)

/* output:

memoryUsage {
  rss: 19365888,
  heapTotal: 3784704,
  heapUsed: 2994680,
  external: 325663,
  arrayBuffers: 9914
}
rss 19.365888mb
heapTotal 3.784704mb
heapUsed 2.99468mb
external 0.325663mb
arrayBuffers 0.009914mb

 */

In the above example, rss (Resident Set Size) represents the amount of memory that was allocated to run the Node process, in this case roughly 19mb.

memoryUsage() provides a few metrics in the returned object. Here's how the Node process docs defines these properties:

heapTotal and heapUsed refer to V8's memory usage.

external refers to the memory usage of C++ objects bound to JavaScript objects managed by V8.

rss, Resident Set Size, is the amount of space occupied in the main memory device (that is a subset of the total allocated memory) for the process, including all C++ and JavaScript objects and code.

arrayBuffers refers to memory allocated for ArrayBuffers and SharedArrayBuffers, including all Node.js Buffers. This is also included in the external value. When Node.js is used as an embedded library, this value may be 0 because allocations for ArrayBuffers may not be tracked in that case.

Using process.memoryUsage() is a topic I'd like to touch on in a variety of scenarios in future gists. There are many topics here that require some research. Just to name a few:

How Node / v8 uses stacks and the heap to manage memory
Garbage Collection in JavaScript
Comparison of Garbage Collection algorithms like mark & sweep
Using WeakMaps, WeakRefs, and WeakSets, and measuring their implementations with process.memoryUsage()
v8's memory management
Chromium's memory snapshot feature, and how it ties into v8 (and how it compares to process.memoryUsage())

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process.memoryUsage() in Node