cache/tips-and-workarounds.md

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## Cache segment restore timeout
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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
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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).
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## Use cache across feature branches
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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.
## 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>