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https://issues.apache.org/jira/browse/MNG-6575?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16751267#comment-16751267
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Hervé Boutemy edited comment on MNG-6575 at 1/24/19 4:03 PM:
-------------------------------------------------------------
when you have many many poms with dependencyManagement inherited, either
immutability permits to share the objects instance, either you have many
clones...
look at MNG-6571 memory dumps and you'll see the difference: VersionRanges are
very much inherited. Before the code change, they were cloned (as much as the
number of modules, then 4000 here), while after the cache (allowed because
instances are immutable), they where a few shared instances
Dependencies are the same story: inherited in general without update, then
instance could be shared. And in the memody dump, you see 4 millions instances,
where it could probably be dropped to 1600
was (Author: hboutemy):
when you have many many poms with dependencyManagement inherited, either
immutability permits to share the objects instance, either you have many
clones...
look at MNG-6571 memory dumps and you'll see the difference: VersionRanges are
very much inherited. Before the code change, they were cloned (as much as the
number of modules, then 4000 here), while after the cache (allowed because
instances are immutable), they where a few shared instances
> make Dependency immutable
> -------------------------
>
> Key: MNG-6575
> URL: https://issues.apache.org/jira/browse/MNG-6575
> Project: Maven
> Issue Type: Improvement
> Components: Dependencies, Inheritance and Interpolation
> Affects Versions: 3.6.0
> Reporter: Hervé Boutemy
> Priority: Major
>
> while working on Maven memory consumption issue MNG-6571, once VersionRange
> is made immutable, memory used was divided by 2: the next big expected win is
> to make Dependency immutable, which would probably once again divide memory
> by 2 because the vast majority of time, dependencies (be it in
> dependencyManagement or base dependencies) are inherited without any
> modification
> this will require to change
> [ModelMerger|https://maven.apache.org/ref/3.6.0/maven-model/apidocs/org/apache/maven/model/merge/ModelMerger.html]
> 's {{mergeDependency(Dependency target, Dependency source, boolean
> sourceDominant, Map<Object,Object> context)}} signature, since is not really
> an immutable friendly signature
> and also make [Dependency
> code|https://maven.apache.org/ref/3.6.0/maven-model/apidocs/org/apache/maven/model/Dependency.html]
> immutable (generated by Modello)
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