🔥 single-command flamegraph profiling 🔥
Discover the bottlenecks and hot paths in your code, with flamegraphs.
0x can profile and generate an interactive flamegraph for a Node process in a single command, on both Linux and OS X. Whilst this seems trivial... it's not. Well it wasn't before 0x.
An example interactive flamegraph can be viewed at http://davidmarkclements.github.io/0x-demo/
This demo shows a terminal preview, the default behaviour
is not to show a preview, you can use -p to turn it on.
Node v4+
OS
npm install -g 0x
Prefix the usual command for starting a process with 0x:
0x node my-app.js
All node args are supported, for instance:
0x node --trace-opt my-app.js
When node flags aren't required, we can use the shorthand form:
0x my-app.js
If we want to test against a local node binary, simply reference the binary directly.
For example if the node binary is the current working directory:
0x ./node my-app.js
Once we're ready to generate a flamegraph we send a SIGINT.
The simplest way to do this is pressing CTRL+C.
When 0x catches the SIGINT, it process the stacks and
generates a profile folder, containing flamegraph.html
Due to security reasons Docker containers tend to result in the following error:
Cannot read kernel map
perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error 1 (Operation not permitted)
perf_event_open(..., 0) failed unexpectedly with error 1 (Operation not permitted)
Error:
You may not have permission to collect stats.
[...]
We can work around this problem by running our container with the --privileged option
or add privileged: true in your docker-compose.yml file.
See the Docker's doc for more info.
Generating a flamegraph can be quite intense on CPU and memory, if we have restricted resources we should generate the flamegraph in two pieces.
First we can use the --stacks-only flag to purely capture stacks.
0x --stacks-only my-app.js #0x on the server
Press ctrl+c when ready, this will create the usual profile folder,
holding one file, that stacks.$PID.out file.
Now we need to transfer the stacks file from our production server to our local dev machine.
Let's say the pid was 7777, we can generate the flamegraph locally with
0x -c gen stacks.7777.out # 0x locally
Now the hard work is done away from production, ensuring we avoid any service-level problems.
As your stack grows you may have memory issues with both Node and your browser.
For Node, run with the following flag
--stack-size=8024
For Chrome, run with the following flag
--js-flags="--stack-size 8024"
Where 8024 is the megabytes of RAM required to run load stack. Adjust this as needed and confirm you have it to spare.
Print usage info
Specify artifact output directory Default: '${process.cwd()}/profile-${PID}(-${Date.now()})?'
Generates an flamegraph.svg file in the artifact output directory,
in addition to the flamegraph.html file.
Generates an SVG file, prerenders SVG inside HTML and outputs a PNG to the terminal (if possible) Depends on imagemagick (brew install imagemagick) If using iTerm 2.9+ image will be output to terminal Warning - depending on the amount of stacks this option can take tens of seconds
Default: false
Milliseconds. Delay before tracing begins (or before stacks are processed in the Linux case), allows us to ignore initialisation stacks (e.g. module loading).
Example: 0x -d 2000 my-app.js
Default: 300
Color code the stacks by JS and C
Example: 0x -l my-app.js
Default: false
A comma separated list
Overrides langs, Color code frames by type
Examples: 0x -t my-app.js
Default: false
Exclude tiers or langs, comma seperated list
Options: v8, regexp, nativeC, nativeJS, core, deps, app, js, c
Examples:
0x -x v8,nativeC,core my-app.js
0x -x c my-app.js
Default: v8
Include tiers, Overwrites exclude. Really only useful for including the v8 tier (which is excluded by default).
Options: v8, regexp, nativeC, nativeJS, core, deps, app, js, c
Example: 0x --include v8 my-app.js
Default: false
Dark or Light theme
Options: dark | light
Example: 0x --theme light my-app.js
Default: dark
Don't generate the flamegraph, only create the stacks
output. If assigned to '-' stacks output will come through
stdout. Use this in combination with the -c gen argument
to generate the flamegraph from raw stacks.
Options: false | true | -
Examples:
0x --stacks-only my-app.js
0x --stacks-only=- my-app.js
Default: false
Show output from dtrace or perf tools
Default: false
Run a "0x command", possible commands are help and gen.
0x -c helpoutputs advanced usage (i.e. the commands).
0x -c genThe gen command will generate the flamegraph from a stacks.out file.
Example: 0x -c gen [flags] profile-$PID/stacks.$PID.out > flamegraph.html
Flags include all the flags that can be passed to 0x
--timestamp-profilesAdds the current timestamp to the Profile Folder's name minimizing collisions for in containerized environments
Example: profile-3866-
By default, a profile folder will be created and named after the PID, e.g.
profile-3866 (we can set this name manually using the --output-dir flag).
The Profile Folder can contain the following files
The is helpful, because there's other things you can do with stacks output. For instance, checkout cpuprofilify and traceviewify.
Want to try it out? Clone this repo, run npm i -g and
from the repo root run
0x examples/rest-api
In another tab run
npm run stress-rest-example
To put some load on the rest server, once that's done use ctrl + c to kill the server.
Now try some other options, e.g.
0x -t examples/rest-api
See ./examples/babel for an example. Note the babel require hook is not currently supported. Notes on using the babel-cli instead can be found in the babel example readme.
Don't use v1, it was an experiment and is non functional Should have be v0...
Yes please!
DEBUG=0x* 0x my-app.js
0x is generously sponsored by nearForm
This tool is essentially a mashup from various info and code sources, and therefore would have taken much longer without the following people and their Open Source/Info Sharing efforts
MIT and Apache (depending on the code, see LICENSE.md)
FAQs
🔥 single-command flamegraph profiling 🔥
The npm package 0x receives a total of 22,664 weekly downloads. As such, 0x popularity was classified as popular.
We found that 0x demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 3 open source maintainers collaborating on the project.
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