Hi All,

We want to create upstream change to Maven to support true incremental build 
for big-sized projects.
To raise a pull request we have to pass long chain of Deutsche Bank's internal 
procedures. So, before starting the process we would like to get your feedback 
regarding this feature.


Our project is hosted in mono-repo and contains ~600 modules. All modules has 
the same SNAPSHOT version.
There are lot of test automation around this, everything is tested before merge 
into release branch.

Current setup helps us to simplify build/release/dependency management for 10+ 
teams those contribute into codebase. We can release everything in 1-click.
The major drawback of such approach is build time: full local build took 45-60 
min (-T8), CI build ~25min(-T16).

To speed-up our build we needed 2 features: incremental build and shared cache.
Initially we started to think about migration to Gradle or Bazel. As migration 
costs for the mentioned tools were too high, we decided to add similar 
functionality into Maven.

Current results we get: 1-2 mins for local build(-T8) if build was cached by 
CI, CI build ~5 mins (-T16).

Feature description:

The idea is to calculate checksum for inputs and save outputs in cache.
Each node checksum calculated with:

*         Effective POM hash

*         Sources hash

*         Dependencies hash (dependencies within multi-module project)

Project sources inputs are searched inside project + all paths from plugins 
How does it work in practice:

1.       CI: runs builds and stores outputs in shared cache

2.       CI: reuse outputs for same inputs, so time is decreasing

3.       Locally: when I checkout branch and run 'install' for whole project, I 
get all actual snapshots from remote cache for this branch

4.       Locally: if I change multiple modules in tree, only changed subtree is 

Impact on current Maven codebase is very localized (MojoExecutor, where we 
injected cache controller).
Caching can be activated/deactivated by property, so current maven flow will 
work as is.

And the big plus is that you don't need to re-work your current project. 
Caching should work out of box, just need to add config in .mvn folder.

Please let us know what do you think. We are ready to invest in this feature 
and address any further feedback.

Kind regards,

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