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cache/tips-and-workarounds.md
Sampark Sharma 192d0bc0f9
Release support for cross-os caching as opt-in feature
Add documentation for cross-os caching
2023-01-06 09:47:29 +00:00

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## Cache segment restore timeout
A cache gets downloaded in multiple segments of fixed sizes (`1GB` for a `32-bit` runner and `2GB` for a `64-bit` runner). Sometimes, a segment download gets stuck which causes the workflow job to be stuck forever and fail. Version `v3.0.8` of `actions/cache` introduces a segment download timeout. The segment download timeout will allow the segment download to get aborted and hence allow the job to proceed with a cache miss.
Default value of this timeout is 60 minutes and can be customized by specifying an [environment variable](https://docs.github.com/en/actions/learn-github-actions/environment-variables) named `SEGMENT_DOWNLOAD_TIMEOUT_MINS` with timeout value in minutes.
## Update a cache
A cache today is immutable and cannot be updated. But some use cases require the cache to be saved even though there was a "hit" during restore. To do so, use a `key` which is unique for every run and use `restore-keys` to restore the nearest cache. For example:
```yaml
- name: update cache on every commit
uses: actions/cache@v3
with:
path: prime-numbers
key: primes-${{ runner.os }}-${{ github.run_id }} # Can use time based key as well
restore-keys: |
primes-${{ runner.os }}
```
Please note that this will create a new cache on every run and hence will consume the cache [quota](./README.md#cache-limits).
## Use cache across feature branches
Reusing cache across feature branches is not allowed today to provide cache [isolation](https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#restrictions-for-accessing-a-cache). However if both feature branches are from the default branch, a good way to achieve this is to ensure that the default branch has a cache. This cache will then be consumable by both feature branches.
## Cross OS cache
From `v3.2.3` cache is cross os compatible when `enableCrossOsArchive` input is passed as true. This means that a cache created on `ubuntu-latest` can be used by `windows-latest` provided the workflow which runs on `windows-latest` have input `enableCrossOsArchive` as true. This is useful when you want to cache dependencies which are available on different the OSs. This will help reduce the consumption of the cache quota. Things to keep in mind while using this feature:
- Only cache those files which are compatible across OSs.
- Caching symlinks might cause issues while restoration as they work differently on different OSs.
- Put runner OS in the cache key if that cache is not meant to be used across OSs to prevent cross-os.
## Force deletion of caches overriding default cache eviction policy
Caches have [branch scope restriction](https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#restrictions-for-accessing-a-cache) in place. This means that if caches for a specific branch are using a lot of storage quota, it may result into more frequently used caches from `default` branch getting thrashed. For example, if there are many pull requests happening on a repo and are creating caches, these cannot be used in default branch scope but will still occupy a lot of space till they get cleaned up by [eviction policy](https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#usage-limits-and-eviction-policy). But sometime we want to clean them up on a faster cadence so as to ensure default branch is not thrashing. In order to achieve this, [gh-actions-cache cli](https://github.com/actions/gh-actions-cache/) can be used to delete caches for specific branches.
This workflow uses `gh-actions-cache` to delete all the caches created by a branch.
<details>
<summary>Example</summary>
```yaml
name: cleanup caches by a branch
on:
pull_request:
types:
- closed
workflow_dispatch:
jobs:
cleanup:
runs-on: ubuntu-latest
steps:
- name: Check out code
uses: actions/checkout@v3
- name: Cleanup
run: |
gh extension install actions/gh-actions-cache
REPO=${{ github.repository }}
BRANCH=${{ github.ref }}
echo "Fetching list of cache key"
cacheKeysForPR=$(gh actions-cache list -R $REPO -B $BRANCH | cut -f 1 )
## Setting this to not fail the workflow while deleting cache keys.
set +e
echo "Deleting caches..."
for cacheKey in $cacheKeysForPR
do
gh actions-cache delete $cacheKey -R $REPO -B $BRANCH --confirm
done
echo "Done"
env:
GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
```
</details>