Synopsis

Tools for profiling Node.js programs. Uses SystemTap to collect and symbolicate JavaScript backtraces, extracting human-readable names by walking the V8 stack and heap. Uses wrapper scripts and node-stackvis to generate textual or HTML flamegraphs. Can also output text suitable for input to to [FlameGraph] (https://github.com/brendangregg/FlameGraph).

Inspired and informed by Dave Pacheco's excellent V8 DTrace ustack helper.

Safety

SystemTap is invasive; recommended to try in safe environments before running in production!

Caveats

• Only works on 64-bit node processes.
• Line numbers are best effort (not always available) and refer to the start of a function.
• Only tested on node0.10 so far.
• Stacks may omit inlined functions.
• Also may elide frames on very deep stacks to avoid doing too much work in SystemTap probe context.

Basic Usage

[~/uber/node-stap]$ sudo cmd/torch.js 
Usage: torch <pid> <text|flame|raw> <duration (s)>
    text: textual flame graph.
    flame: html flame graph.
    raw: format suitable for input to FlameGraph tools.

HTML Example

dh@dh:~/node-stap$ sudo cmd/torch.js 24701 flame 10 > /tmp/flame.html
Sampling 24701 for 10s, outputting flame.

dh@dh:~/node-stap$ # done

Raw Example

dh@dh:~/node-stap$ sudo node cmd/torch.js 2291 raw 10 > ../raw.txt
Sampling 2291 for 10s, outputting raw.

dh@dh:~/node-stap$ cd ../FlameGraph/
dh@dh:~/FlameGraph$ ./stackcollapse.pl < ../raw.txt  > ../collapsed.txt
dh@dh:~/FlameGraph$ ./flamegraph.pl < ../collapsed.txt  > ../flame.svg

Text Example

dh@dh:~/node-stap$ cat ../test.js
var dummy = new Error().stack; // Persuade v8 to compute line numbers

while(true) {
    console.log("Hello!");
}
dh@dh:~/node-stap$ node ../test.js  > /dev/null & 
[1] 2291
dh@dh:~/node-stap$ sudo node cmd/torch.js 2291 text 10
Sampling 2291 for 10s, outputting text.

Total samples: 747
747 node::Start(int, char**):[native]
  747 node::Load(v8::Handle<v8::Object>):[native]
    747 v8::Function::Call(v8::Handle<v8::Object>, int, v8::Handle<v8::Value>*):[native]
      747 v8::internal::Execution::Call(v8::internal::Handle<v8::internal::Object>, v8::internal::Handle<v8::internal::Object>, int, v8::internal::Handle<v8::internal::Object>*, bool*, bool):[native]
        747 [0x72a82a in /usr/bin/nodejs]:[native]
          747 [entry frame]
            747 [internal frame]
              747 [empty]:[unknown]:26
                747 startup:[unknown]:29
                  747 Module.runMain:module.js:494
                    747 Module._load:module.js:274
                        ... [more]

Installation

You'll need SystemTap and headers for your kernel version installed on your system. Other than that, just clone and profile as above. Tested with SystemTap 2.7 on linux 3.2.0-79-generic.

Tests

All things in the fullness of time.

Contributors

dh

Future Work

32-bit processes, edge cases in native code symbolication.

License

node-stap is available under the MIT license. See the LICENSE file for more info.