NameNode运行原理浅析

来源：互联网发布：软件质量管理部门职责编辑：程序博客网时间：2024/06/16 05:39

hadoop版本：Apache Hadoop 2.6.0

instance的role type主要有3个，namenode，secondary namenode和data node；其他的还有balancer，backup node等

1.HDFS存储在本地操作系统磁盘的目录结构

NameNode：

/data/dfs/nn/current

-rw-r--r-- 1 hdfs hdfs 322K Apr 17 08:41 edits_0000000000007093753-0000000000007096223

-rw-r--r-- 1 hdfs hdfs 338K Apr 17 09:41 edits_0000000000007096224-0000000000007098803

-rw-r--r-- 1 hdfs hdfs 361K Apr 17 10:41 edits_0000000000007098804-0000000000007101548

-rw-r--r-- 1 hdfs hdfs 1.0M Apr 17 11:13 edits_inprogress_0000000000007101549

-rw-r--r-- 1 hdfs hdfs 53M Apr 17 09:41 fsimage_0000000000007098803

-rw-r--r-- 1 hdfs hdfs 62 Apr 17 09:41 fsimage_0000000000007098803.md5

-rw-r--r-- 1 hdfs hdfs 53M Apr 17 10:41 fsimage_0000000000007101548

-rw-r--r-- 1 hdfs hdfs 62 Apr 17 10:41 fsimage_0000000000007101548.md5

-rw-r--r-- 1 hdfs hdfs 8 Apr 17 10:41 seen_txid

-rw-r--r-- 1 hdfs hdfs 173 Nov 13 12:05 VERSION

Secondary NameNode：

/data1/dfs/snn/current

-rw-r--r-- 1 hdfs hdfs 322K Apr 17 08:41 edits_0000000000007093753-0000000000007096223

-rw-r--r-- 1 hdfs hdfs 338K Apr 17 09:41 edits_0000000000007096224-0000000000007098803

-rw-r--r-- 1 hdfs hdfs 361K Apr 17 10:41 edits_0000000000007098804-0000000000007101548

-rw-r--r-- 1 hdfs hdfs 53M Apr 17 09:41 fsimage_0000000000007098803

-rw-r--r-- 1 hdfs hdfs 62 Apr 17 09:41 fsimage_0000000000007098803.md5

-rw-r--r-- 1 hdfs hdfs 53M Apr 17 10:41 fsimage_0000000000007101548

-rw-r--r-- 1 hdfs hdfs 62 Apr 17 10:41 fsimage_0000000000007101548.md5

-rw-r--r-- 1 hdfs hdfs 173 Apr 17 10:41 VERSION

2.NameNode中一共有4种文件：

edits_{x}_{y}：和fsimage已经merger过的transaction记录文件，x为起始transaction记号，y为截止号

edits_inprogress_{y}：尚未和fsimage merger过的transaction记录文件，y为transaction截止号

fsimage_{y}：namenode的namespace存在本地的checkpoint文件，存储了y为transaction截止号；一般会有两个，文件生成时间间隔为设置的checkpoint生成间隔时间；

*NameNode上只有在启动时才会合并最新的fsimage_{y}和edits_inprogress_{y}文件

NameNode时序图：

上图中第三步最新的配置为：

1.fs.checkpoint.period, dfs.namenode.checkpoint.period：The time between two periodic file system checkpoints.

2.dfs.namenode.checkpoint.txns:The number of transactions after which the NameNode or SecondaryNameNode will create a checkpoint of the namespace, regardless of whether the checkpoint period has expired.

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