memory-usage

A readable stream that samples and emits memory usage over time.

You can for instance use the output to graph your memory usage.

Can also be used from the command line to chart the memory usage of a Node.js app directly in a web browser.

Installation

For CLI usage:

npm install memory-usage -g

For programmatic usage:

npm install memory-usage --save

CLI Usage Example

Use the memory-usage command instead of the node command:

memory-usage server.js

The memory usage of server.js will now be displayed live in your default web browser:

Programmatic Usage Example

Sample memory usage every 2 seconds and write it to a CSV file:

var fs = require('fs')
var csvWriter = require('csv-write-stream')
var memoryUsage = require('memory-usage')

memoryUsage(2000)
  .pipe(csvWriter())
  .pipe(fs.createWriteStream('memory.csv'))

Note that you application of course have to do some actual work. If you just run the example above as is, the node process will simply exit after creating an empty file.

If you want to chart the memory usage, I recommend combining this module with chart-csv.

API

`stream = memoryUsage([freq|options])`

Will start sampling memory usage every freq milliseconds (defaults to 5000) as soon as the stream is flowing.

The optional options object expects the following properties:

freq - The sampling frequency in milliseconds (defaults to 5000)
ts - A boolean specifying if a timestamp should be outputtet along with the memory samples (defaults to false)
gc - A boolean specifying if garbage collection should be profiled and logged along with the memory samples (defaults to false)

The stream emits samples in the form of JavaScript objects:

{
  rss: 4935680,       // Resident set size: Memory assigned to the process in bytes
  heapTotal: 1826816, // V8 heap memory allocated in bytes
  heapUsed: 650472,   // V8 heap memory used in bytes
  ts: 1479179912921,  // UNIX epoch timestamp for sample in milliseconds (only present if `options.ts` is `true`)
  gc: null            // Indicates if sample was taken after a garbage collection run (only present if `options.gc` is `true`)
}

If the gc property is null, it means that the sample wasn't taken after a garbage collection run. If the value is a string, it will indicate the type of garbage collection run. Currently, the values can be either Scavenge or MarkSweepCompact.

Note that samples indicating a garbage collection run might be a few hundred milliseconds delayed. This means that you might see a regular timed sample appear prior in the stream with reduced memory usage, even though there's no official indication of a garbage collection run yet.

License

This program is available as open source under the terms of the MIT License.

watson/memory-usage