heapdump-signal

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 instead, it's easy!

Inspecting the snapshot (taken from node-heapdump)

Open Google Chrome 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).