CI: does the cache save us time?

[warner]

If you look at the timings on https://github.com/Agoric/agoric-sdk/pull/489/checks?check_run_id=426471769 , it looks like we're spending 5 minutes hashing the go.sum and yarn.lock files to conclude that nothing has changed and thus we don't need to save the cache.

I'm guessing that the sheer number of files in go/pkg/mod and node_modules means anything which traverses **/ is going to take forever, so we might want to change those to 1: only hash the single top-level yarn.lock (since there shouldn't be any others), 2: is there a similar top-level go.sum we could hash instead of finding all 67 of them?, 3: do we really need to invalidate these caches when those checksum files change anyways?

The caches in question are only about 90MB each, so I'm not sure we're saving time overall there. Maybe we should just omit the cache actions from our .github/actions/test-all-packages.yml?

[michaelfig]

1 and 2 are absolutely right... Only the top-level yarn.lock and packages/cosmic-swingset/go.sum are needed.

I'll put together a PR and benchmark it.

Thanks for raising this, @warner

[michaelfig]

This behaviour was fixed in actions/runner#268 but it has not yet been deployed to Github. I'm looking to find an ETA for when Github's Actions will deploy the fix.

[michaelfig]

At @dtribble's request, I have disabled the cache in https://github.com/Agoric/agoric-sdk/commits/4cae3360d645a1ebe8dd707fa07e75b6a446e9c3

Leaving this issue open to revisit (and revert that commit) once Github Actions have deployed the fix described above. If it's past 2020-04-01, try doing that!

[michaelfig]

Now the cache saves us time!