Cache pip packages per version rather than per project

[stsewd]

We are currently saving the pip cache per project, which can lead to some weird deps problems when building from different versions.

https://github.com/rtfd/readthedocs.org/blob/768856e3f72fd0ec1e4fbe9eab8913cb5f01b490/readthedocs/projects/models.py#L616-L621

Ref #5680 (comment)

[humitos]

which can lead to some weird deps problems when building from different versions.

What are these problems?

[stsewd]

Different versions have different requirements, dependencies of another dependencies, etc.

[stsewd]

Also if the cache gets corrupted, users need to wipe in order to get it working again.

And we can't clean the cache in #5680

[humitos]

Also if the cache gets corrupted, users need to wipe in order to get it working again.

I don't think we are having this problem.

And we can't clean the cache in #5680

There is no need to save a cache if we are going to clean it after use it once. If that's what we want, we just don't need to save the cache at all. We can use,

• do not mount a a volume outside the docker container
• use --no-cache-dir option in pip

Having a per-version pip cache does not makes too much sense to me.

[agjohnson]

I'm going to close this, I think it goes against our goal of removing caching entirely. If we weren't on this path, it would be a helpful feature, but I think the benefits ephemeral build process bring will trump any gains by tuning caching