heapdump-signal/README.md

Automatically write a heapdump upon SIGUSR2

heapdump-signal
===

Replacement for `node-heapdump` (native module) to trigger the built-in Node V8 API to write a heapdump upon receiving `SIGUSR2`.

### Usage

Require the module somewhere in your code.

    require('heapdump-signal');

On UNIX platforms, you can force a snapshot by sending the node.js process
a SIGUSR2 signal:

    $ kill -USR2 <pid>

If you want to respond to a different signal or write to a different path, use the [v8.writeHeapSnapshot API](https://nodejs.org/api/v8.html#v8writeheapsnapshotfilenameoptions) instead, it's easy!

### Inspecting the snapshot (taken from `node-heapdump`)

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 (taken from `node-heapdump`)

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).