The blogpost has a lot of technical details, but you can also just read the code and try it yourself:
- Our approach writes new cache entries all the time. This can get expensive, and is a pretty big change in behavior from how actions/setup-go works today.
- actions/setup-go can basically be considered incredibly critical infrastructure for the public golang ecosystem. Any change in behavior is probably very risky and slow to happen. At this point I'd bet that we see no change, ever, in behavior.
Additionally there are a few relevant issues/prs that have been ignored for years so I'm not optimistic about contributing upstream. Frankly what we've done is write a very small bit of glue code that is likely most effective as a reference for teams writing their own custom caching actions that fit their exact needs:
- https://github.com/actions/setup-go/pull/426
- https://github.com/actions/setup-go/issues/630
- https://github.com/actions/setup-go/issues/395
- https://github.com/actions/setup-go/issues/596
That said we'd be happy if someone used our code and found it valuable! Lukas put a ton of effort into cleaning up my initial version, added the cache trimming, etc. We depend on this for all of our jobs and use it every day and think it's quite good.
- Allowing actions/setup-go users to specify a cache key prefix so that they can have more than one golang CI job, each with its own cache: this is 100% worth upstreaming. I believe there are existing requests and PRs about this. Up to you guys to implement however you see fit.
- Allowing "always update the cache": also a good idea to enable as an option, very important for non-open-source teams that are trying to maximize cache hit rate.
- Allowing "trim the cache": if you're going to allow always updating the cache, probably a good idea.
But the "always update" and "trim" cache changes combine to have a lot of risks regarding cache poisoning that might be bad for open source projects. Lukas may have a different opinion or more to say on this front.
> - Allowing actions/setup-go users to specify a cache key prefix so that they can have more than one golang CI job, each with its own cache [...]
I'd actually go further: this may be a sensible default behavior.
"Always update the cache" can get expensive, but it's a neat one; "trim the cache" is definitely necessary if you enable this in a moderately active repository in our experience.
If you want really out-there ideas: rather than storing and loading the full cache monolithically, you could use a GitHub-specific GOCACHEPROG and Go-specific cache service to load only the active items. The pruning problem goes away because accretion is cheap. In theory, parallel jobs could actually share this joint cache. (This may not be a realistic initiative at GitHub.)
If you can raise feedback with your colleagues —
- The docs and settings for Actions Cache limits are really hard to navigate; at some pointed we desperately wanted to pay GitHub more money for more cache, but couldn't figure out why we were capped.
- Bulk-data endpoints for Actions performance would be a boon for optimization projects like this. I wind up either scraping `gh run` (slow) or setting up a GitHub App to collect perf data through webhooks (initially tedious, has to be continuously available).
All this aside — actions/setup-go is a pretty well-considered default and an essential part of writing Go on GitHub; ty for your work maintaining it!
My 2c given that that issue has sat in TODO for several years with no movement is that the maintainers probably aren't going to be pursuing too many big swings like that.
End of the day, implementing an efficient GOCACHE with github's cache primitives is untenable for the general case IMO. It works by shipping around big tarballs, and when your cache actually needs fine grained access to thousands of usually tiny files, only a few of which change, you're likely gonna spend more time on transfer and unpacking than you gain with cache hits.
The other thing is, as mentioned elsewhere, it's really hard to measure cache perf at a granular enough level, and aggregate that across jobs, so I'm willing to bet most people don't (outside of this very good post!) and are going off of vibes or napkin math and don't realize they're wasting time caching garbage.
I’ve long wondered why setup-go was so slow and expensive it’s great to see improvements made.
It only gets a brief mention, but the cache-pruning change was an interesting one. Cache accretion happens in the default actions/setup-go too, but dramatically increasing the number of cache-writes for cloudx-io/setup-go made it an actual issue.
As the cache grows, so does the time it takes to load it from GitHub's actions cache... and that grows until it's a significant time-suck in CI. We prune with basic mark-and-sweep.
Digging deeper, the pluggable `GOCACHEPROG` (introduced in Go 1.24) is a really useful tool. Shimming the normal cache logic for measurement, for example. In theory this should also be attractive for remote caching.
The trick was to run back over our git history and calculate, for each commit,
1. The test package Go cache keys at that point
2. The GitHub actions/cache keys constructed by actions/setup-go and cloudx-io/setup-go respectively
Once you have these mappings, you can
1. Pick some arbitrary HEAD commit
2. Model which prior GitHub cache blob would be loaded under each action
3. Compare the test package Go cache keys in that loaded blob against those for HEAD to determine which test packages would run vs. skip
Might write this up in greater depth sometime soon.
However, other people around me are fine with apt installs and pip installs from global mirrors in every CI run. So I may be just autistic.
In some cases baking a dependency into an image is signing myself up for perpetual toil to keep the image CVE free.
- WillAbides/setup-go-faster speeds up the Go toolchain setup (literally installing Go)
- cloudx-io/setup-go uses the slower actions/setup-go toolchain setup, but changes cache strategy so your `go test` and `go build` steps do less work
Those strategies are compatible. I hadn't heard of setup-go-faster — thanks for putting me on to it.
If you're deciding between one or the other, it'll probably come down to which inefficiency predominates in your codebase (i.e. how many tests you have, how quickly they run, and how much real churn there is in your test package build graph).
- uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6
if: ${{ inputs.setup-go == 'true' }}
with:
path: |
${{ env.gocache }}
${{ env.gomodcache }}
key: ${{ runner.os }}-${{ runner.arch }}-go${{ steps.go-setup.outputs.go-version }}-${{ hashFiles('go.sum') }}-${{ env.today }}
restore-keys: |
${{ runner.os }}-${{ runner.arch }}-go${{ steps.go-setup.outputs.go-version }}-${{ hashFiles('go.sum') }}-
${{ runner.os }}-${{ runner.arch }}-go${{ steps.go-setup.outputs.go-version }}-
Like with all things CI, your mileage will vary according to where you write your code and what the code does.