小编Nic*_*ite的帖子

RDD map和mapPartitions方法有什么区别？并且flatMap表现得像map或喜欢mapPartitions？谢谢.

(编辑)即,两者之间的差异(在语义上或在执行方面)

  def map[A, B](rdd: RDD[A], fn: (A => B))
               (implicit a: Manifest[A], b: Manifest[B]): RDD[B] = {
    rdd.mapPartitions({ iter: Iterator[A] => for (i <- iter) yield fn(i) },
      preservesPartitioning = true)
  }

和:

  def map[A, B](rdd: RDD[A], fn: (A => B))
               (implicit a: Manifest[A], b: Manifest[B]): RDD[B] = {
    rdd.map(fn)
  }

同步日志记录会因为可能阻塞而导致性能损失.是否有一个独立的Ruby库来执行异步日志记录(log4r似乎不是)？我可以修改标准库记录器以异步记录吗？我正在寻找像log4j的AsyncAppender这样的东西 - 但最好是利用Ruby的代码块将尽可能多的工作转移到后台线程的实现.

当我在eclipse的"Servers"选项卡上双击我的tomcat服务器时,我将进入propeties页面.此页面只有一个选项卡"概述",并以红色方块作为其图标.当我单击"概述"选项卡上的"打开启动配置"链接时,我会收到两条弹出消息:

创建启动配置选项卡时发生异常原因:没有为启动配置类型定义选项卡组org.eclipse.jst.server.tomcat.core.launchConfigurationType

和:

没有为启动配置类型Apache Tomcat定义选项卡

Eclipse的"错误日志"选项卡包含:

eclipse.buildId=M20090917-0800
java.version=1.6.0_17
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=win32, ARCH=x86, WS=win32, NL=en_GB
Framework arguments:  -product org.eclipse.epp.package.java.product
Command-line arguments:  -os win32 -ws win32 -arch x86 -product org.eclipse.epp.package.java.product -data C:\devsrc

Error
Mon Jan 18 13:38:01 GMT 2010
Unhandled event loop exception
java.lang.NullPointerException
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationManager.filterLaunchDelegates(LaunchConfigurationManager.java:267)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationTabGroupViewer.hasMultipleDelegates(LaunchConfigurationTabGroupViewer.java:1138)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationTabGroupViewer.hasDuplicateDelegates(LaunchConfigurationTabGroupViewer.java:1121)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationTabGroupViewer.getErrorMesssage(LaunchConfigurationTabGroupViewer.java:1163)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationsDialog.updateMessage(LaunchConfigurationsDialog.java:1433)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationsDialog.refreshStatus(LaunchConfigurationsDialog.java:1159)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationTabGroupViewer.refreshStatus(LaunchConfigurationTabGroupViewer.java:989)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationTabGroupViewer$8.run(LaunchConfigurationTabGroupViewer.java:692)
    at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationTabGroupViewer.inputChanged(LaunchConfigurationTabGroupViewer.java:697)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationTabGroupViewer.setInput0(LaunchConfigurationTabGroupViewer.java:659)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationTabGroupViewer.setInput(LaunchConfigurationTabGroupViewer.java:635)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationPropertiesDialog.initializeContent(LaunchConfigurationPropertiesDialog.java:126)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationsDialog.createContents(LaunchConfigurationsDialog.java:425)
    at org.eclipse.jface.window.Window.create(Window.java:431)
    at org.eclipse.jface.dialogs.Dialog.create(Dialog.java:1089)
    at org.eclipse.debug.internal.ui.launchConfigurations.LaunchConfigurationsDialog.create(LaunchConfigurationsDialog.java:354)
    at …

如果我有代码:

int f(int a) { return a; }
double f(double g) { return g; }

int main()
{
    int which = f(1.0f);
}

调用f的哪个重载,为什么？