cypress: Performance regression in CI from 6.6 -> 6.7 (and 6.8/7.0)

Current behavior

Cypress got slower in v6.7.

Desired behavior

That it’s about as fast as 6.6. (or faster! 😉 )

Details

My team is using Cypress with Gitlab CI, and when upgrading from 6.6 to 6.7 our test jobs slowed significantly. (Cypress suites taking 2-3x the time)

I can’t share the code, so I produced a new project that demonstrates a performance regression, hopefully for the same reasons:

https://github.com/jrr/cypress-storybook-example

The project contains two Cypress suites - the example tests that came out of the box, and a separate suite that visits storybook pages (containing miscellaneous Material-UI React components).

Locally (2018 Macbook Pro) the performance difference is negligible. In CI, though, there’s noticeable slowdown:

Suite	Environment	6.6	6.7	6.8	7.0	7.2
Visit Storybook	Local	0:27 0:26	0:27 0:27	0:31 0:28	0:29 0:30	0:31 0:30
Visit Storybook	GitHub	0:55 0:54 1:07	1:44 1:28 2:05	2:04 2:11 1:53	1:39 1:45 1:43	1:10 1:03 1:03
Visit Storybook	GitLab	2:54 2:53 2:54	5:53 5:15 6:01	5:23 5:27 4:57	5:09 4:45 4:48	4:25 3:26 4:33
Cypress Examples	Local	1:14 1:16	1:20 1:21	1:21 1:21	1:34 1:28	1:22 1:23
Cypress Examples	GitHub	1:31 1:25 1:27	1:48 1:40 1:49	2:03 2:09 1:42	1:45 1:54 1:46	1:27 1:20 1:22
Cypress Examples	GitLab	2:03 1:53 1:48	3:32 3:32 3:21	3:21 3:30 3:04	3:28 3:07 3:01	2:03 1:55 2:01

(Using Chrome --headless. I tried a few runs in case of outliers.)

Both GitHub Actions and GitLab CI are connected to the project repo and logs are publicly visible:

Both jobs are running tests in the cypress/browsers:node14.16.0-chrome89-ff86 Docker environment.

Gitlab’s “shared runners” are rather meager - 3.75GB of RAM and 1 vCPU. GitHub’s are slightly beefier with 7GB and 2 CPUs.

Here’s what’s reported by cypress info:

// GitHub
Cypress Version: 6.6.0
System Platform: linux (Debian - 10.8)
System Memory: 7.29 GB free 1.16 GB

// Gitlab
Cypress Version: 6.6.0
System Platform: linux (Debian - 10.8)
System Memory: 3.87 GB free 573 MB

I’m not sure where the bottleneck is (e.g. CPU, Memory, Disk). Are you aware of performance regression in the last couple of versions? Does Cypress maintain performance tests to catch major deltas from release to release? (it looks like cypress-real-world-app tests may have gotten a bit slower according to its dashboard)

Is there anything I can try to further track it down and/or improve it?

Side Note 1: Retained Prereleases

I started trying to bisect commits between 6.6 and 6.7 to track down what change introduced the performance regression (using the install pre-release version guide), but I didn’t get far before I hit the end of the prerelease packages.

Could you retain them for longer? Like, say, 3 or 4 releases worth? The prerelease packages are great for trying out the latest bleeding edge, but they could also be great for bisecting history if they were available longer.

Side Note 2: Cypress Stress Test

If you take the storybook test in this repo, and crank it up from 50 visits to ~300, it starts out pretty zippy:

https://user-images.githubusercontent.com/164652/113465256-a4291a00-9400-11eb-9472-c12df185a037.mp4

But by the end it gets real slow:

https://user-images.githubusercontent.com/164652/113465259-abe8be80-9400-11eb-90e0-a09c7dc4af1d.mp4

Do you know what’s going on here? I thought it might be useful as a stress/performance test if you don’t already have something like this.

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edit: added numbers for Cypress 7.0 edit: added numbers for Cypress 7.2