Added tips and workarounds for cross os

README.md

@@ -28,7 +28,6 @@ See ["Caching dependencies to speed up workflows"](https://docs.github.com/en/ac
 * Fix zstd not working for windows on gnu tar in issues.
 * Allowing users to provide a custom timeout as input for aborting download of a cache segment using an environment variable `SEGMENT_DOWNLOAD_TIMEOUT_MINS`. Default is 60 minutes.
 * Two new actions available for granular control over caches - [restore](restore/action.yml) and [save](save/action.yml)
-* Add support for cross os caching. For example, a cache saved on windows can be restored on ubuntu and vice versa.
 
 Refer [here](https://github.com/actions/cache/blob/v2/README.md) for previous versions
 
@@ -245,6 +244,7 @@ Following are some of the known practices/workarounds which community has used t
 - [Cache segment restore timeout](./tips-and-workarounds.md#cache-segment-restore-timeout)
 - [Update a cache](./tips-and-workarounds.md#update-a-cache)
 - [Use cache across feature branches](./tips-and-workarounds.md#use-cache-across-feature-branches)
+- [Improving cache restore performance on Windows/Using cross-os caching](./tips-and-workarounds.md#improving-cache-restore-performance-on-windows-using-cross-os-caching)
 - [Force deletion of caches overriding default cache eviction policy](./tips-and-workarounds.md#force-deletion-of-caches-overriding-default-cache-eviction-policy)
 
 #### Windows environment variables

RELEASES.md

@@ -59,4 +59,7 @@
 ### 3.2.1
 - Update `@actions/cache` on windows to use gnu tar and zstd by default and fallback to bsdtar and zstd if gnu tar is not available. ([issue](https://github.com/actions/cache/issues/984))
 - Added support for fallback to gzip to restore old caches on windows.
-- Added logs for cache version in case of a cache miss.
+- Added logs for cache version in case of a cache miss.
+
+### 3.2.2
+- Reverted the changes made in 3.2.1 to use gnu tar and zstd by default on windows.

tips-and-workarounds.md

@@ -19,6 +19,24 @@ A cache today is immutable and cannot be updated. But some use cases require the
 ## 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.
 
+## Improving cache restore performance on Windows/Using cross-os caching
+Currently, cache restore is slow on Windows due to tar being inherently slow and the compression algorithm `gzip` in use. `zstd` is the default algorithm in use on linux and macos. It was disabled on Windows due to issues with bsd tar(libarchive), the tar implementation in use on Windows. 
+
+To improve cache restore performance, we can re-enable `zstd` as the compression algorithm using the following workaround. Add the following step to your workflow before the cache step:
+
+```yaml
+    - if: ${{ runner.os == 'Windows' }}
+      name: Use GNU tar
+      shell: cmd
+      run: |
+        echo "Adding GNU tar to PATH"
+        echo C:\Program Files\Git\usr\bin>>"%GITHUB_PATH%"
+```
+
+The `cache` action will use GNU tar instead of bsd tar on Windows. This should work on all Github Hosted runners as it is. For self-hosted runners, please ensure you have GNU tar and `zstd` installed.
+
+The above workaround is also needed if you wish to use cross-os caching since difference of compression algorithms will result in different cache versions for the same cache key. So the above workaround will ensure `zstd` is used for caching on all platforms thus resulting in the same cache version for the same cache key.
+
 ## 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.