[MRESOLVER-228] Improve the maven dependency resolution speed by a skip & reconcile approach - ASF JIRA

Details

Type: Improvement
Status: Closed
Priority: Major
Resolution: Duplicate
Affects Version/s: 1.7.2
Fix Version/s: None
Component/s: Resolver
Labels:
None

Description

When comes to resolve the huge amount of dependencies of an enterprise level project, the maven resolver is very slow to resolve the dependency graph/tree. Take one of our app as example, it could take 10minutes+ and 16G memory to print out the result of mvn dependency:tree.

This is because there are many dependencies declared in the project, and some of the dependencies would introduce 600+ transitive dependencies, and exclusions are widely used to solve dependency conflicts.

By checking the code, we know the exclusion is also part of the cache key. This means when the exclusions up the tree differs, the cached resolution result for the same GAV won't be picked up and need s to be recalculated.

From above figure, we know:

In 1st case, D will be resolved only once as there are no exclusions/same exclusions up the tree.
In 2nd case, the B and C have different exclusions and D needs to be recalculated, if D is a heavy dependency which introduce many transitive dependencies, all D and its children needs to be recalculated. Recalculating all of these nodes introduces 2 issues:
- Slow in resolving dependencies.
- Lots of DependencyNodes cached (all calculated/recalculated nodes would be cached) and will consume huge memory.

To improve the speed of maven resolver's dependency resolution, I implemented a skip & reconcile approach. Here is the skip part.

From above figure, the 1st R is resolved at depth 3, and the 2nd R is resolved again because the depth is at 2 which is lower, the 3rd R at depth 3 and the 4th R at depth 4 are simply skipped as R is already resolved at depth 2. This is because the same node with deeper depth is most likely won't be picked up by maven as maven employs a "nearest transitive dependency in the tree depth and the first in resolution" strategy.

The 3rd R and 4th R will have children set as zero and marked as skipped by the R at depth 2 in 2nd tree path.

Here is the reconcile part:

When there are dependency conflicts, some of the skipped nodes need to be reconciled.

In above figure, there are 4 tree paths.

The D1 (D with version 1) in the 1st tree path is get resolved, children of E and R at depth 3 are resolved and cached.
In the 2nd tree path, when resolving E & R of H, we simply skip these 2 nodes as they are in deeper depth (depth: 4) than the E & R in 1st tree path.
In the 3rd tree path, a R node with lower path is resolved, and a E node at depth 5 is skipped.
In the 4th path, a D2 (D with version 2) node is resolved, as the depth is lower than D1, so maven will pick D2, this means the E & R's children cached in tree depth 1 should be discarded.

Thus we might need to reconcile the E & R nodes in 2nd, 3rd and 4th tree paths. Here only E in 2nd tree path needs to be reconciled. This is because:

R in 3rd tree path won't be picked up as there is already a R in 2nd tree path with a lower depth.
E in 3rd tree path won't be picked up as it is enough to reconcile the E in 2nd tree path as the E in 2nd tree path is deeper than E in 3rd tree path.

Here is what we've updated in the maven-resolver logic:

Resolve dependencies by leveraging a skip approach. The node in deeper depth will be skipped if a node with same GAV has been resolved with a lower depth.
Cloned the nodes in step 1.
Use maven's ConflictResolver (Transformer) to transform the cloned nodes and find out the conflict winners & the nodes to reconcile.
Ex, D1 conflicts with D2 in above digram.
E in 2nd tree path will be reconciled.
Reconcile all skipped nodes identified in above step.

After we enabled the resolver patch in maven, we are seeing 10% ~70% build time reduced for different projects depend on how complex the dependencies are, and the result of mvn dependency:tree and mvn dependency:list remain the same.

We've verified the resolver performance patch leveraging an automation solution to certify 2000+ apps of our company by comparing the mvn dependency:tree and mvn dependency:list result with/without the performance patch.

Please help review the PR.
https://github.com/apache/maven-resolver/pull/136