[GitHub] [maven] gnodet commented on pull request #530: [MNG-7235] Speed improvements when calculating the sorted project graph

[GitBox <gi...@apache.org>]

gnodet commented on pull request #530:
URL: https://github.com/apache/maven/pull/530#issuecomment-919434406


   > I will try to review and understand your change this week.
   
   @michael-o  Let me give you a few details.
   
   I performed a time analysis on the quite big project (1300 modules or so) with a `mvnd help:evaluate -Dexpression=project.version` run.  `mvnd` does compute the whole graph at the beginning.
   This leads to a call to `getDownstreamProjects()` for each project in the build. 
   
   Currently, this means for each call, going through all projects and calling `projectIds.contains( ProjectSorter.getId( mavenProject ) )`.  The new version caches a few things (the order of the projects so that the dependent projects can be sorted without iterating through the whole list of projects), and a mapping of `ProjectSorter.getId(x) -> x` to avoid recomputing the ids.
   In addition to those two caches, the loop is changed so that we retrieve the projects and sort them.
   
   So, if `N` is the number of projects, this brings down the number of iteration from `N * N` to `a * N`, where `a` is the mean number of downstream projects. And `a` is usually very small (especially in my case where we only get the first level of dependencies between modules and not the transitive ones).  In addition, the number of `getId()` calls is down to `N`, which was the critical spot.
   
   Hopes this helps.
   


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