profiling Node.js applications

# profiling Node.js applications

Patrick Mueller
[`@pmuellr`](https://twitter.com/pmuellr),
[`muellerware.org`](http://muellerware.org)<br>
principal software engineer at [Elastic](https://elastic.co)<br>

May 2019

<div class="smaller"><div class="smaller"><div class="smaller">
<a href="http://pmuellr.github.io/slides/2019/05-profiling-node">
         http://pmuellr.github.io/slides/2019/05-profiling-node
</a>
<br>
<a href="http://pmuellr.github.io/slides/">
         http://pmuellr.github.io/slides/
</a>
(all of Patrick's slides)
</div></div></div>

---

<div class="page-icon">
<span class="smaller"><span class="smaller"><span class="smaller">
<tt>profiling Node.js applications</tt>
</span></span></span>
</div>

---

## what is profiling?

* gaining insight into what your code is doing

* typically involving finding out:

* why your code is so slow!

* what are you doing with all that memory!

---

## why should you profile your code?

* save money

* run with less RAM
  * run with less CPU

* delight customers

* your app runs faster

---

## what kind of profiling for Node.js?

**<u>performance</u>** with V8's CPU profiler

**<u>memory</u>** with V8's heap snapshots

Debugging built into V8, accessed by Chrome Dev Tools.

---

## using the tools

* start your app with the Node.js `--inspect` option

* open URL [`chrome://inspect/`](chrome://inspect/) in Chrome

* click the **inspect** link under **Remote Target**

---

---

<div class="page-icon">
<span class="smaller"><span class="smaller"><span class="smaller">
<tt>profiling Node.js applications</tt>
</span></span></span>
</div>

---

# profiling performance

---

<div class="page-context">
<span class="smaller"><span class="smaller"><span class="smaller">
<tt>profiling performance</tt>
</span></span></span>
</div>

<div class="page-icon">
<span class="smaller"><span class="smaller"><span class="smaller">
<tt>profiling Node.js applications</tt>
</span></span></span>
</div>

---

## what does V8's CPU profiler do?

* **start profiler**: at regular intervals, V8 will capture current stack trace, with
  time stamp, and source file / line numbers

* **stop profiler**: profiler will aggregate the stack trace information,
  and produce a JSON data structure for analysis tools

---

## what does Chrome DevTools show?

* timeline of stacks of functions executed

* sort by aggregated function execution time

* intro: [Google Developers: Speed Up JavaScript Execution](https://developers.google.com/web/tools/chrome-devtools/profile/rendering-tools/js-execution?hl=en)

---

## demo: profiling `cpu-hawg`

`node --inspect` [`cpu-hawg.js`][cpu-hawg.js]

[cpu-hawg.js]: https://github.com/pmuellr/slides/blob/gh-pages/2019/05-profiling-node/demos/cpu-hawg.js

---

## for a "real life" profile ...

node --inspect-brk `which npm` outdated

---

<div class="page-icon">
<span class="smaller"><span class="smaller"><span class="smaller">
<tt>profiling Node.js applications</tt>
</span></span></span>
</div>

---

# profiling memory

---

<div class="page-context">
<span class="smaller"><span class="smaller"><span class="smaller">
<tt>profiling memory</tt>
</span></span></span>
</div>

<div class="page-icon">
<span class="smaller"><span class="smaller"><span class="smaller">
<tt>profiling Node.js applications</tt>
</span></span></span>
</div>

---

## what are V8 heap snapshots?

* JSON file describing every reachable JavaScript object in the application;
  taking a snapshot always starts with a garbage collection

* JSON files are ... large; figure 2x heap memory allocated by Node.js

---

## what does Chrome DevTools show?

* count / size of objects grouped by **class**

* compare old and new heapshots to show object diff counts

* follow object references, both directions

* intro: [Google Developers: Viewing Heap Snapshots](https://developers.google.com/web/tools/chrome-devtools/profile/memory-problems/heap-snapshots)

---

## demo: profiling `mem-hawg`

`node --inspect` [`mem-hawg.js`][mem-hawg.js]

[mem-hawg.js]: https://github.com/pmuellr/slides/blob/gh-pages/2019/05-profiling-node/demos/mem-hawg.js

---

<div class="page-icon">
<span class="smaller"><span class="smaller"><span class="smaller">
<tt>profiling Node.js applications</tt>
</span></span></span>
</div>

---

# other tools

---

## profiling tools

* [NodeSource N|Solid](https://nodesource.com/products/nsolid)

* enhanced Node runtime and console with profiling tools and visualizers

* [NearForm Clinic.js](https://clinicjs.org/)

* command-line cpu profiling tools and visualizers

---

## hacking CPU profiles

https://pmuellr.github.io/no-pro/

* alt-visualizer for v8 cpu profile files

* group functions by package and module

---

<div class="page-icon">
<span class="smaller"><span class="smaller"><span class="smaller">
<tt>profiling Node.js applications</tt>
</span></span></span>
</div>

---

# `fin`