GitLab CI: which directories can safely be cached?

Some background Right now, our GitLab CI pipeline takes ~ 10 minutes to complete. The generation of thumbnails seems to be a major factor:

[..]
success Building production JavaScript and CSS bundles - 58.614s
success Rewriting compilation hashes - 0.001s
success run queries - 77.167s - 42/42 0.54/s
success Generating image thumbnails - 232.075s - 760/760 3.27/s
success Building static HTML for pages - 15.758s - 36/36 2.28/s
info Done building in 272.523996685 sec
[..]

Build times are reduced drastically when .cache and public are cached in .gitlab-ci.yml:

[..]
success Building production JavaScript and CSS bundles - 29.286s
success run queries - 29.868s - 2/2 0.07/s
success Building static HTML for pages - 7.725s - 36/36 4.66/s
info Done building in 56.332283976 sec
[..]

Question In all Gatsby-related .gitlab-ci.yml-examples I’ve seen so far, only node_modules/ is cached. This leaves me wondering if it’s safe to cache .cache and public in CI. If it’s safe to do so, why doesn’t this example list those folders?

Long story short: can both .cache and public safely be cached in a GitLab CI environment?

[jonniebigodes]

a while ago i encountered a issue with some stale images and one page that shouldn’t exist because the it’s source content was no longer present. Don’t know if that’s the case still i honestly haven’t had the time to test it thoroughly, probably someone else more knowledgeable can give some further insights on this.

[jooola]

@sidharthachatterjee Hello, something seems inconsistent on whether to cache the public and/or .cache folders. In my Gitlab CI build logs I see the following:

[...]
info We've detected that the Gatsby cache is incomplete (the .cache directory exists
but the public directory does not). As a precaution, we're deleting your site's
cache to ensure there's no stale data.
success initialize cache - 0.063s
success copy gatsby files - 0.026s
success onPreBootstrap - 0.010s
success  gatsby-source-wordpress  ensuring plugin requirements are met - 0.730s
⠀
info  gatsby-source-wordpress  
	This is either your first build or the cache was cleared.
	Please wait while your WordPress data is synced to your Gatsby cache.
	Maybe now's a good time to get up and stretch? :D
[...]

So either the previous PR #22501 is missing a folder, or the deletion of the .cache folder is not correct.

What should we do ?

EDIT: Nevermind I didn’t look at the full PR changes, a last commit did add the public folder.