[jira] [Commented] (MRESOLVER-228) Improve the maven dependency resolution speed by a skip & reconcile approach

["Michael Osipov (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MRESOLVER-228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17449834#comment-17449834 ] 

Michael Osipov commented on MRESOLVER-228:
------------------------------------------

Please take a look at MNG-6357, this might break your understanding of the second diagram.

> Improve the maven dependency resolution speed by a skip & reconcile approach
> ----------------------------------------------------------------------------
>
>                 Key: MRESOLVER-228
>                 URL: https://issues.apache.org/jira/browse/MRESOLVER-228
>             Project: Maven Resolver
>          Issue Type: Improvement
>          Components: Resolver
>    Affects Versions: 1.7.2
>            Reporter: wei cai
>            Priority: Major
>         Attachments: Screen Shot 2021-11-27 at 12.58.26 PM.png, Screen Shot 2021-11-27 at 12.58.59 PM.png, Screen Shot 2021-11-27 at 12.59.32 PM.png
>
>
> 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|https://github.com/apache/maven-resolver/blob/master/maven-resolver-impl/src/main/java/org/eclipse/aether/internal/impl/collect/DefaultDependencyCollector.java#L500], 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. 
> !Screen Shot 2021-11-27 at 12.58.26 PM.png!
> 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.
> !Screen Shot 2021-11-27 at 12.58.59 PM.png!
> 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:
> !Screen Shot 2021-11-27 at 12.59.32 PM.png!
> 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.
>  * Use maven's ConflictResolver (Transformer) to find out the conflict winners. Figure out the node that conflict with the winner. Ex, g:a:D1 conflicts with g:a:D2 in above case.
>  * Find out all skipped nodes that is getting affected with D1 as D1 is the loser and D2 is the winner.
>  * Reconcile all skipped nodes in above step, for nodes with same GAVs, only the node with the lowest path will be reconciled.
>  
> 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]
>  
> Another approach comes to my mind is we could modify the ConflictResolver to make it reconcile the nodes, the logic would be:
>  * Resolve dependencies by leveraging a skip approach. The node in deeper depth will be skipped if a node with same GAV has been resolved in a lower depth.
>  * Modify the [ConflictResolver|#L183],] when the ConflictResolves determines the winner and find it has been skipped, it should do the reconcile immediately.
> The question here is maven-resolver-impl relies on the maven-resolver-util where the ConflictResolver resides, and in the ConflictResolver, it again need do the reconcile which agains depends on maven-resolver-impl. This is some sort of cyclic dependency. Probably we should go this way:
> The DefaultDependencyCollector should pass a IDependencyReconciler to ConflictResolver, the ConflictResolver can then do the reconcile when it considers it is mandatory. Please share your expertise on how to make the code clean, tidy and maintainable. It would be my great honor to refine the PR until it meets your accept criteria.
>  
>  



--
This message was sent by Atlassian Jira
(v8.20.1#820001)