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Hadoop - namenode未启动(Hadoop - namenode is not starting up)

 我试图以root用户身份运行hadoop，当Hadoop文件系统运行时，我执行了namenode格式命令hadoop namenode -format 。  
 在此之后，当我尝试启动名称节点服务器时，它显示如下所示的错误  
13/05/23 04:11:37 ERROR namenode.FSNamesystem: FSNamesystem initialization failed.
java.io.IOException: NameNode is not formatted.
        at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:330)
        at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:100)
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.initialize(FSNamesystem.java:411)
 
 我试图寻找任何解决方案，但找不到任何明确的解决方案。  
 任何人都可以建议  
 谢谢。 

I am trying to run hadoop as a root user, i executed namenode format command hadoop namenode -format when the Hadoop file system is running. 
After this, when i try to start the name node server, it shows error like below 
13/05/23 04:11:37 ERROR namenode.FSNamesystem: FSNamesystem initialization failed.
java.io.IOException: NameNode is not formatted.
        at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:330)
        at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:100)
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.initialize(FSNamesystem.java:411)
 
I tried to search for any solution, but cannot find any clear solution. 
Can anyone suggest? 
Thanks.

原文：https://stackoverflow.com/questions/16713011

更新时间：2021-11-30 11:11

最满意答案

 1.我需要了解的所有命名约定是什么？  
 db表是复数，模型是单数，控制器是复数。 因此您拥有由users表支持的User模型，并可通过UsersController查看。  
 文件应该命名为类名的wide_cased版本。 所以FooBar类需要放在一个名为foo_bar.rb的文件中。 如果您使用模块命名空间，命名空间需要由文件夹来表示。 所以如果我们谈论Foo::Bar类，它应该在foo/bar.rb 。  
 2.控制器操作应如何构建和命名？  
 控制器操作应该是RESTful。 这意味着您应该将您的控制器视为公开资源，而不仅仅是启用RPC。 Rails具有成员操作与资源收集操作的概念。 成员动作是在特定实例上运行的，例如/users/1/edit将是用户的编辑成员动作。 收集行动是对所有资源进行操作的东西。 所以/users/search?name=foo会是一个集合操作。  
 上面的教程描述了如何在您的路线文件中实际实现这些想法。  
 3.什么是在视图中呈现信息的最佳方式（通过:content_for或呈现部分内容）以及我不应该使用哪些方式？  
 当您希望能够将内部模板中的html附加到外部模板时，应该使用content_for ，例如，可以将视图模板中的某些内容附加到布局模板中。 一个很好的例子是添加一个页面特定的JavaScript。  
# app/views/layout/application.rb
<html>
  <head>
    <%= yield :head %>
...

# app/views/foobars/index.html.erb

<% content_for :head do %>
  <script type='text/javascript'>
    alert('zomg content_for!');
  </script>
<% end %>
 
 部分文件要么分解大文件，要么多次渲染相同位置的信息。 例如  
<table>
  <%= render :partial => 'foo_row', :collection => @foobars %>
</table>

# _foo_row.html.erb

<tr>
 <td>
  <%= foobar.name %>
 </td>
</tr>
 
 4.什么应该进入帮手，什么不应该？  
 你的模板应该只有基本的分支逻辑。 如果你需要做更激烈的事情，它应该是一个帮手。 视图中的局部变量对世界上所有的好和正确的东西都是可憎的，所以这是一个很好的迹象，你应该帮助你。  
 另一个原因是纯粹的代码重用。 如果你只是一次又一次地做同样的事情，把它拉到一个帮手（如果它是完全一样的东西，它应该是在一个部分）。  
 5.什么是常见的陷阱或我需要从一开始就正确做的事情？  
 partials不应直接引用实例（@）变量，因为它会阻止重新使用该行。 总是将数据通过:locals => { :var_name => value }参数传递给render函数。  
 保持与视图呈现没有直接关系的视图之外的逻辑。 如果你有选择在视图中做某件事，并在其他地方做某件事，那么在其他地方做9次是更好的选择。  
 我们在轨道上有一个“脂肪模型，瘦身控制器”的口头禅。 一个原因是模型是面向对象的，控制器是非程序化的。 另一个是模型可以跨越控制器，但控制器不能跨越模型。 第三是模型更具可测性。 它只是一个好主意。  
 6.你如何模块化代码？ 这是lib文件夹的用途吗？  
 lib文件夹用于跨越模型问题的代码（即，不是模型的东西，但将被多个模型使用）。 当你需要在那里放置某些东西时，你会知道，因为你无法弄清楚应该使用什么模型。在这之前，你可以忽略lib。  
 需要注意的是，从rails 3开始，lib不在自动加载路径上，这意味着您需要任何内容（或将其添加回）  
 一种自动需要lib目录中所有模块的方法：  
#config/initializers/requires.rb
Dir[File.join(Rails.root, 'lib', '*.rb')].each do |f|
  require f
end

1. What are all naming conventions I need to be aware of? 
db table is plural, model is singular, controller is plural. so you have the User model that is backed by the users table, and visible through the UsersController. 
files should be named as the wide_cased version of the class name. so the FooBar class needs to be in a file called foo_bar.rb. If you are namespacing with modules, the namespaces need to be represented by folders. so if we are talking about Foo::Bar class, it should be in foo/bar.rb. 
2. How should controller actions be structured and named? 
controller actions should be RESTful. That means that you should think of your controllers as exposing a resource, not as just enabling RPCs. Rails has a concept of member actions vs collection actions for resources. A member action is something that operates on a specific instance, for example /users/1/edit would be an edit member action for users. A collection action is something that operates on all the resources. So /users/search?name=foo would be a collection action.  
The tutorials above describe how to actually implement these ideas in your routes file. 
3. What are the best ways to render information in a view (via :content_for or render a partial) and what are ways I shouldn't use? 
content_for should be used when you want to be able to append html from an inner template to an outer template -- for example, being able to append something from your view template into your layout template. A good example would be to add a page specific javascript. 
# app/views/layout/application.rb
<html>
  <head>
    <%= yield :head %>
...

# app/views/foobars/index.html.erb

<% content_for :head do %>
  <script type='text/javascript'>
    alert('zomg content_for!');
  </script>
<% end %>
 
partials are either for breaking up large files, or for rendering the same bit of information multiple times. For example 
<table>
  <%= render :partial => 'foo_row', :collection => @foobars %>
</table>

# _foo_row.html.erb

<tr>
 <td>
  <%= foobar.name %>
 </td>
</tr>
 
4.What should go into a helper and what shouldn't? 
your templates should only have basic branching logic in them. If you need to do anything more intense, it should be in a helper. local variables in views are an abomination against all that is good and right in the world, so that is a great sign that you should make a helper. 
Another reason is just pure code reuse. If you are doing the same thing with only slight variation over and over again, pull it into a helper (if it is the exact same thing, it should be in a partial).  
5. What are common pitfalls or something I need to do correctly from the very beginning? 
partials should never refer directly to instance (@) variables, since it will prevent re-use down the line. always pass data in via the :locals => { :var_name => value } param to the render function.  
Keep logic out of your views that is not directly related to rendering your views. If you have the option to do something in the view, and do it somewhere else, 9 times out of 10 doing it somewhere else is the better option. 
We have a mantra in rails that is "fat models, skinny controllers". One reason is that models are object oriented, controllers are inherantly procedural. Another is that models can cross controllers, but controllers cant cross models. A third is that models are more testable. Its just a good idea. 
6. How can you modularize code? Is that what the lib folder is for? 
the lib folder is for code that crosses the concerns of models (i.e. something that isn't a model, but will be used by multiple models). When you need to put something in there, you will know, because you wont be able to figure out what model to put it in. Until that happens, you can just ignore lib. 
Something to keep in mind is that as of rails 3, lib is not on the autoload path, meaning that you need to require anything you put in there (or add it back in) 
A way to automatically require all modules in the lib directory: 
#config/initializers/requires.rb
Dir[File.join(Rails.root, 'lib', '*.rb')].each do |f|
  require f
end

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