Event-loop-chart

Visualize the lag of the event loop of your Nodejs application.

What is event loop lag?

It is a metric that can help to spot synchronous functions in your Nodejs application. The event loop allows to execute non blocking i/o operations as long as this operations are asynchronous. Please check better explanations of the event loop functionality but in short, there is a queue of operations to be executed, if any of those operations is synchronous like fs.readFileSync('/file.md') the event loop is blocked until the operation is finished. The time that the event loop is blocked is called event loop lag.

How do you use Event-loop-chart?

Install the npm dependency:

npm install event-loop-chart

Init the library with data collection interval time and outpug path of the chart:

const elc = require('event-loop-chart');
// set the interval of collection of the event loop lag percentiles for 5000ms
elc.init(5000,"/path/output.png");

And that is it! Every 5 seconds, you application will output a line chart with the percentil values p10, p25, p50, p95 and p99.

To trigger a snapshot:

elc.snapshot("/path/output.png");

The unit used to measure the lag is nanoseconds. You can have a look at this documentation if you want to know more.