4、NameNode启动过程详解

NameNode

• 内存
• 本地磁盘
  • fsimage
  • edits

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第一次启动HDFS

1. 格式化HDFS，目的就是生成fsimage
2. start NameNode，读取fsimage文件
3. start DataNode，向NameNode注册；block report（块汇报）
4. create dir /user/hw/tmp -> write [edits]
5. put files /user/beifeg/tmp(*-site.xml) -> write [edits]
6. delete file /user/beifeng/tmp/core-site.xml -> write [edits]

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第二次启动HDFS

1. NameNode
   • read [fsimage]
   • read [edits]
   • gen write fsimage [new]
   • gen edits [null]
2. DataNode
   • 注册
   • block report
3. create dir /user/beifeng/tmp -> write [edits]
4. put files /user/beifeg/tmp(*-site.xml) -> write [edits]
5. delete file /user/beifeng/tmp/core-site.xml -> write [edits]

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SecondaryNameNode辅助功能讲解

• NameNode中的编辑日志文件太大的话如何处理。需要借助SecondaryNameNode.
• 定期的合并 fsimage+edits ->new fsimage