title: Nexus: maven repository parallel connection limitation?
body: <p>Our project intensively uses Maven3 for build, and a private Nexus (version 2.2) repository is used to host the snapshot builds and proxy artifacts from outside. It works fine.</p>
  
  <p>Recently I am trying to speed up our maven build with parallel (-T parameter), and some random build failures are observed from time to time. The failures are mainly caused by failed dependency resolution, which is rarely happened in none parallel mode. </p>
  
  <p>My question: is it possibly caused by parallel connection limitation in Nexus? Or any other possibility?</p>
  
  <p>Thanks.</p>
  
  <p>The build contains 20+ modules which usually takes 10 minutes to finish.
  Here is the failure I got yesterday evening:</p>
  
  <pre><code>00:11:11 [ERROR] Failed to execute goal on project app-common: Could not     resolve dependencies for project com.abc.sbo.occ:app-common:jar:1.3.0-SNAPSHOT: Failed to collect dependencies for [com.abc.sbo.occ:common-test:jar:1.3.0-SNAPSHOT (test), com.abc.sbo.occ:bo-frw-common:jar:1.3.0-SNAPSHOT (compile), org.apache.poi:poi:jar:3.9 (compile), org.apache.poi:poi-ooxml:jar:3.9 (compile), net.sf.jxls:jxls-core:jar:1.0.2 (compile), com.aspose.cells:aspose-cells:jar:8.2.1 (compile), junit:junit:jar:4.11 (test), org.mockito:mockito-all:jar:1.9.5 (test), nl.jqno.equalsverifier:equalsverifier:jar:1.1.3 (test), org.codehaus.sonar-plugins.java:sonar-jacoco-listeners:jar:1.2 (test)]: Failed to read artifact descriptor for commons-lang:commons-lang:jar:2.6: Could not find artifact org.apache:apache:pom:7 -&gt; [Help 1]
  00:11:11 [ERROR] 
  00:11:11 [ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
  00:11:11 [ERROR] Re-run Maven using the -X switch to enable full debug logging.
  00:11:11 [ERROR] 
  00:11:11 [ERROR] For more information about the errors and possible solutions, please read the following articles:
  00:11:11 [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/DependencyResolutionException
  00:11:11 [ERROR] 
  00:11:11 [ERROR] After correcting the problems, you can resume the build with the command
  00:11:11 [ERROR]   mvn &lt;goals&gt; -rf :app-common
  </code></pre>
  
  <p>Update: I toggled the -X option and caught below stack trace after one day's run. The declared missing artifact org.apache:apache:pom:7 does exist in Nexus for a long time. Maybe it indicates I have to upgrade Nexus to latest version?</p>
  
  <pre><code>14:00:47 [ERROR] Failed to execute goal on project app-common: Could not resolve dependencies for project com.abc.sbo.occ:app-common:jar:1.3.0-SNAPSHOT: Failed to collect dependencies for [com.abc.sbo.occ:common-test:jar:1.3.0-SNAPSHOT (test), com.abc.sbo.occ:bo-frw-common:jar:1.3.0-SNAPSHOT (compile), org.apache.poi:poi:jar:3.9 (compile), org.apache.poi:poi-ooxml:jar:3.9 (compile), net.sf.jxls:jxls-core:jar:1.0.2 (compile), com.aspose.cells:aspose-cells:jar:8.2.1 (compile), junit:junit:jar:4.11 (test), org.mockito:mockito-all:jar:1.9.5 (test), nl.jqno.equalsverifier:equalsverifier:jar:1.1.3 (test), org.codehaus.sonar-plugins.java:sonar-jacoco-listeners:jar:1.2 (test)]: Failed to read artifact descriptor for commons-lang:commons-lang:jar:2.6: Could not find artifact org.apache:apache:pom:7 -&gt; [Help 1]
  14:00:47 org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal on project app-common: Could not resolve dependencies for project com.abc.sbo.occ:app-common:jar:1.3.0-SNAPSHOT: Failed to collect dependencies for [com.abc.sbo.occ:common-test:jar:1.3.0-SNAPSHOT (test), com.abc.sbo.occ:bo-frw-common:jar:1.3.0-SNAPSHOT (compile), org.apache.poi:poi:jar:3.9 (compile), org.apache.poi:poi-ooxml:jar:3.9 (compile), net.sf.jxls:jxls-core:jar:1.0.2 (compile), com.aspose.cells:aspose-cells:jar:8.2.1 (compile), junit:junit:jar:4.11 (test), org.mockito:mockito-all:jar:1.9.5 (test), nl.jqno.equalsverifier:equalsverifier:jar:1.1.3 (test), org.codehaus.sonar-plugins.java:sonar-jacoco-listeners:jar:1.2 (test)]
  14:00:47    at org.apache.maven.lifecycle.internal.LifecycleDependencyResolver.getDependencies(LifecycleDependencyResolver.java:210)
  14:00:47    at org.apache.maven.lifecycle.internal.LifecycleDependencyResolver.resolveProjectDependencies(LifecycleDependencyResolver.java:117)
  14:00:47    at org.apache.maven.lifecycle.internal.MojoExecutor.ensureDependenciesAreResolved(MojoExecutor.java:258)
  14:00:47    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:201)
  14:00:47    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
  14:00:47    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
  14:00:47    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
  14:00:47    at org.apache.maven.lifecycle.internal.LifecycleThreadedBuilder$1.call(LifecycleThreadedBuilder.java:167)
  14:00:47    at org.apache.maven.lifecycle.internal.LifecycleThreadedBuilder$1.call(LifecycleThreadedBuilder.java:163)
  14:00:47    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
  14:00:47    at java.util.concurrent.FutureTask.run(FutureTask.java:166)
  14:00:47    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
  14:00:47    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
  14:00:47    at java.util.concurrent.FutureTask.run(FutureTask.java:166)
  14:00:47    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
  14:00:47    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
  14:00:47    at java.lang.Thread.run(Thread.java:722)
  14:00:47 Caused by: org.apache.maven.project.DependencyResolutionException: Could not resolve dependencies for project com.abc.sbo.occ:app-common:jar:1.3.0-SNAPSHOT: Failed to collect dependencies for [com.abc.sbo.occ:common-test:jar:1.3.0-SNAPSHOT (test), com.abc.sbo.occ:bo-frw-common:jar:1.3.0-SNAPSHOT (compile), org.apache.poi:poi:jar:3.9 (compile), org.apache.poi:poi-ooxml:jar:3.9 (compile), net.sf.jxls:jxls-core:jar:1.0.2 (compile), com.aspose.cells:aspose-cells:jar:8.2.1 (compile), junit:junit:jar:4.11 (test), org.mockito:mockito-all:jar:1.9.5 (test), nl.jqno.equalsverifier:equalsverifier:jar:1.1.3 (test), org.codehaus.sonar-plugins.java:sonar-jacoco-listeners:jar:1.2 (test)]
  14:00:47    at org.apache.maven.project.DefaultProjectDependenciesResolver.resolve(DefaultProjectDependenciesResolver.java:158)
  14:00:47    at org.apache.maven.lifecycle.internal.LifecycleDependencyResolver.getDependencies(LifecycleDependencyResolver.java:185)
  14:00:47    ... 16 more
  14:00:47 Caused by: org.sonatype.aether.collection.DependencyCollectionException: Failed to collect dependencies for [com.abc.sbo.occ:common-test:jar:1.3.0-SNAPSHOT (test), com.abc.sbo.occ:bo-frw-common:jar:1.3.0-SNAPSHOT (compile), org.apache.poi:poi:jar:3.9 (compile), org.apache.poi:poi-ooxml:jar:3.9 (compile), net.sf.jxls:jxls-core:jar:1.0.2 (compile), com.aspose.cells:aspose-cells:jar:8.2.1 (compile), junit:junit:jar:4.11 (test), org.mockito:mockito-all:jar:1.9.5 (test), nl.jqno.equalsverifier:equalsverifier:jar:1.1.3 (test), org.codehaus.sonar-plugins.java:sonar-jacoco-listeners:jar:1.2 (test)]
  14:00:47    at org.sonatype.aether.impl.internal.DefaultDependencyCollector.collectDependencies(DefaultDependencyCollector.java:258)
  14:00:47    at org.sonatype.aether.impl.internal.DefaultRepositorySystem.collectDependencies(DefaultRepositorySystem.java:308)
  14:00:47    at org.apache.maven.project.DefaultProjectDependenciesResolver.resolve(DefaultProjectDependenciesResolver.java:150)
  14:00:47    ... 17 more
  14:00:47 Caused by: org.sonatype.aether.resolution.ArtifactDescriptorException: Failed to read artifact descriptor for commons-lang:commons-lang:jar:2.6
  14:00:47    at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom(DefaultArtifactDescriptorReader.java:331)
  14:00:47    at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.readArtifactDescriptor(DefaultArtifactDescriptorReader.java:186)
  14:00:47    at org.sonatype.aether.impl.internal.DefaultDependencyCollector.process(DefaultDependencyCollector.java:412)
  14:00:47    at org.sonatype.aether.impl.internal.DefaultDependencyCollector.process(DefaultDependencyCollector.java:544)
  14:00:47    at org.sonatype.aether.impl.internal.DefaultDependencyCollector.collectDependencies(DefaultDependencyCollector.java:240)
  14:00:47    ... 19 more
  14:00:47 Caused by: org.apache.maven.model.resolution.UnresolvableModelException: Could not find artifact org.apache:apache:pom:7
  14:00:47    at org.apache.maven.repository.internal.DefaultModelResolver.resolveModel(DefaultModelResolver.java:126)
  14:00:47    at org.apache.maven.model.building.DefaultModelBuilder.readParentExternally(DefaultModelBuilder.java:813)
  14:00:47    at org.apache.maven.model.building.DefaultModelBuilder.readParent(DefaultModelBuilder.java:664)
  14:00:47    at org.apache.maven.model.building.DefaultModelBuilder.build(DefaultModelBuilder.java:310)
  14:00:47    at org.apache.maven.model.building.DefaultModelBuilder.build(DefaultModelBuilder.java:232)
  14:00:47    at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom(DefaultArtifactDescriptorReader.java:322)
  14:00:47    ... 23 more
  14:00:47 Caused by: org.sonatype.aether.resolution.ArtifactResolutionException: Could not find artifact org.apache:apache:pom:7
  14:00:47    at org.sonatype.aether.impl.internal.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:538)
  14:00:47    at org.sonatype.aether.impl.internal.DefaultArtifactResolver.resolveArtifacts(DefaultArtifactResolver.java:216)
  14:00:47    at org.sonatype.aether.impl.internal.DefaultArtifactResolver.resolveArtifact(DefaultArtifactResolver.java:193)
  14:00:47    at org.apache.maven.repository.internal.DefaultModelResolver.resolveModel(DefaultModelResolver.java:122)
  14:00:47    ... 28 more
  14:00:47 Caused by: org.sonatype.aether.transfer.ArtifactNotFoundException: Could not find artifact org.apache:apache:pom:7
  14:00:47    at org.sonatype.aether.impl.internal.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:528)
  14:00:47    ... 31 more
  14:00:47 [ERROR] 
  14:00:47 [ERROR] 
  14:00:47 [ERROR] For more information about the errors and possible solutions, please read the following articles:
  14:00:47 [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/DependencyResolutionException
  14:00:47 [ERROR] 
  14:00:47 [ERROR] After correcting the problems, you can resume the build with the command
  14:00:47 [ERROR]   mvn &lt;goals&gt; -rf :app-common
  </code></pre>