https://github.com/bnoordhuis/node-heapdump

Make a dump of the V8 heap for later inspection.
https://github.com/bnoordhuis/node-heapdump

Last synced: 9 days ago
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Make a dump of the V8 heap for later inspection.

• Host: GitHub
• URL: https://github.com/bnoordhuis/node-heapdump
• Owner: bnoordhuis
• License: other
• Created: 2012-08-10T13:28:33.000Z (about 12 years ago)
• Default Branch: master
• Last Pushed: 2022-04-08T11:07:00.000Z (over 2 years ago)
• Last Synced: 2024-10-29T23:19:22.621Z (10 days ago)
• Language: JavaScript
• Size: 81.1 KB
• Stars: 2,492
• Watchers: 47
• Forks: 130
• Open Issues: 7
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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• awesome-nodejs - node-heapdump - Make a dump of the V8 heap for later inspection.  (Repository / Performance Profiling/Analysis)
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README

        
node-heapdump

===

Make a dump of the V8 heap for later inspection.

### Install

    npm install heapdump

### Build

    node-gyp configure build

### Usage

Load the add-on in your application:

    var heapdump = require('heapdump');

The module exports a single `writeSnapshot([filename], [callback])` function

that writes out a snapshot.  `filename` defaults to

`heapdump-..heapsnapshot` when omitted.

    heapdump.writeSnapshot('/var/local/' + Date.now() + '.heapsnapshot');

The function also takes an optional callback function which is called upon

completion of the heap dump.

    heapdump.writeSnapshot(function(err, filename) {

      console.log('dump written to', filename);

    });

The snapshot is written synchronously to disk.  When the JS heap is large,

it may introduce a noticeable "hitch".

On UNIX platforms, you can force a snapshot by sending the node.js process

a SIGUSR2 signal:

    $ kill -USR2 

The SIGUSR2 signal handler is enabled by default but you can disable it

by setting `NODE_HEAPDUMP_OPTIONS=nosignal` in the environment:

    $ env NODE_HEAPDUMP_OPTIONS=nosignal node script.js

Catch the SIGUSR2 signal to write the snapshot to a custom location:

```js

if (!/nosignal/.test(process.env.NODE_HEAPDUMP_OPTIONS)) {

  process.on("SIGUSR2", function() {

    heapdump.writeSnapshot('/var/local/' + Date.now() + '.heapsnapshot');

  });

}

```

### Inspecting the snapshot

Open [Google Chrome](https://www.google.com/intl/en/chrome/browser/) and

press F12 to open the developer toolbar.

Go to the `Memory` tab, right-click in the tab pane and select

`Load profile...`.

Select the dump file and click `Open`.  You can now inspect the heap snapshot

at your leisure. Some snapshots may take a long time to load, on the order of

minutes or even hours.

Note that Chrome will refuse to load the file unless it has the `.heapsnapshot`

extension.

### Caveats

On UNIX systems, the rule of thumb for creating a heap snapshot is that it

requires memory twice the size of the heap at the time of the snapshot.

If you end up with empty or truncated snapshot files, check the output of

`dmesg`; you may have had a run-in with the system's OOM killer or a resource

limit enforcing policy, like `ulimit -u` (max user processes) or `ulimit -v`

(max virtual memory size).