hadoop - 需要澄清一些基本的HDFS术语

Question

什么是图像，检查点，什么是日记？

在我读过的一个博客中(链接:http://www.aosabook.org/en/hdfs.html)，它说HDFS中的图像是“inode和定义名称系统元数据的块列表”；我不确定这句话是什么意思...

他们还解释说，“检查点”是“存储在NameNode本地本地文件系统中的图像的持久记录”；在此声明中，什么是“永久记录”？

期刊与这两个概念有何关系？

在此先感谢您的帮助!

Answer 1

What is an image, a checkpoint, and what is a journal?

在该链接上都有非常清晰的描述...

Files and directories are represented on the NameNode by inodes. Inodes record attributes like permissions, modification and access times, namespace and disk space quotas.

The inodes and the list of blocks that define the metadata of the name system are called the image. [...] The persistent record of the image stored in the NameNode's local native filesystem is called a checkpoint.

The NameNode records changes to HDFS in a write-ahead log called the journal

至于你的其他问题

"the inode and the list of blocks that define the metadata of the name system"; I was not sure what this sentence means...

如果您读的是一个Inode(和一个块)，那么图像就是定义名称系统元数据的inode和块的集合……确实没有另一种描述方式。也许您需要查找元数据的定义？

what is referring to as a "persistent record"?

查找持久性的定义。检查点是存储在HDFS上特定时间点的图像“快照”。

how is journal related to those two concepts?

日记记录了对HDFS的所有更改。写入图像和检查点的过程对HDFS进行了更改