As Conan 2 continues to evolve, we’re excited to announce the recent release of Conan 2.0.14. This update introduces new features aimed at enhancing productivity and efficiency in production environments. In this post, we’ll focus on two recent additions: Cache Save/Restore and LRU (Least Recently Used) Cleanup.

Save and Restore Packages from/to the Cache

This feature is designed for temporary package movement, offering an efficient way to transfer packages between different Conan caches. It is ideal for scenarios like:

  • CI Pipelines: It facilitates the sharing of intermediate build stages or dependencies across different jobs. Particularly beneficial for parallel jobs, as the Conan cache is not concurrent.

  • Air-Gapped Environments: Useful where direct internet access is restricted, and packages must be transferred via the client side.

It’s crucial to note that saving and restoring packages is a short-term mechanism and not intended for long-term storage or as a backup strategy. The storage format and serialization, although effective within the same Conan version, may not be stable or compatible with future Conan versions. For long-term backup of Conan packages, server-side backup strategies are recommended.

How It Works

For example, imagine we are building our application in CI for three different platforms. The main job in our CI would trigger the three different builds on different agents.

Conan cache save/restore

After each build, you could save a selection of packages from the cache in a tgz for each platform using the conan cache save command. As an argument for the command, you can pass a reference pattern (like in the conan list command) or a package-list json file. Let’s save the latest revision of all packages in the Conan cache:

# save the last revision of all packages in the cache
$ conan cache save "*/*:*" --file=conan_cache_save_linux.tgz
Saving app/2.71: p/autoc5f0e65aa481c3
Saving app/2.71:da39a3ee5e6b4b0d3255bfef95601890afd80709: p/autocf3e6879dde7f6/p
Saving bzip2/1.0.8: p/bzip2b261b4dea28b4
Saving bzip2/1.0.8:e3dc948df7773c2c60edf3a72557250108721b20: p/bzip23cfe2c0da64ba/p
Saving cmake/3.27.7: p/cmake9a3eb5e13dc53
Saving cpp-httplib/0.11.3: p/cpp-hd3892a337ccc3
Saving eigen/3.4.0: p/eigenecaf3dc594b0c
# creates conan_cache_save_linux.tgz

The saved .tgz file encompasses recipe folders, package metadata, and other essential contents, excluding temporary folders like “build” or “download”. You save the packages for each parallel job and at the end of each job, stash them to later recover in the main job where you can restore all the saved packages in the Conan cache by using conan cache restore:

$ conan cache restore conan_cache_save.tgz 
Restore: app/2.71 in p/autoc5f0e65aa481c3
Restore: app/2.71:da39a3ee5e6b4b0d3255bfef95601890afd80709 in p/autocf3e6879dde7f6/p
Restore: bzip2/1.0.8 in p/bzip2b261b4dea28b4
Restore: bzip2/1.0.8:e3dc948df7773c2c60edf3a72557250108721b20 in p/bzip23cfe2c0da64ba/p
Restore: cmake/3.27.7 in p/cmake9a3eb5e13dc53
Restore: cpp-httplib/0.11.3 in p/cpp-hd3892a337ccc3
Restore: eigen/3.4.0 in p/eigenecaf3dc594b0c

For more details on how to use this feature, please refer to the Conan documentation.

LRU: Removing Unused Packages from the Cache

Conan now supports an LRU (Least Recently Used) policy to efficiently manage cache size. This feature is important for maintaining an optimized package cache as the Conan cache does not implement any automatic expiration policy, so its size will always increase unless packages are removed or the cache is cleared from time to time.

How It Works

The use of the LRU feature is through the --lru argument of the conan remove and conan list commands. You can use it to remove old package binaries or to remove recipes along with their associated binaries. The LRU time follows the rules of the remove command. If we are removing recipes with a “*” pattern, only the LRU times for recipes will be checked. If a recipe has been recently used, it will keep all the binaries, and if the recipe has not been recently used, it will remove itself and all its binaries.

For example, if we want to remove all binaries (but not recipes) not used in the last 2 months, we would do:

$ conan remove "*:*" --lru=2M -c

To also remove all recipes (and their associated binaries):

$ conan remove "*" --lru=2M -c

You could also use the conan list command to generate a list of the least recently used packages with the LRU argument, and then pass the generated package-list to the conan remove command. An equivalent approach for the removal of all recipes and packages not used in the last two months would be:

# List all unused (last 2 months) recipe revisions
$ conan list "*#*" --lru=2M --format=json > old.json
# Remove those recipe revisions (and their binaries)
$ conan remove --list=old.json -c


The addition of the cache save/restore and LRU cleanup features in Conan significantly enhances efficiency, particularly in CI environments, and will assist in maintaining optimal performance in production.

For more detailed information and examples, visit our DevOps Guide and the Other Features Tutorial.

We are keen to hear your thoughts and suggestions about these new features. Please don’t hesitate to share your experiences and ideas on GitHub issues.