what is the meaning of namespace and metadata whic

问题:

As a beginner to hadoop I am confused with these words namespace and metadata. Is there any relation between these two ?

回答1:

According to 'Hadoop The definitive guide' - "The NameNode manages the filesystem namespace. It maintains the filesystem tree and the metadata for all the files and directories in the tree."

Essentially, Namespace means a container. In this context it means the file name grouping or hierarchy structure.

Metadata contains things like the owners of files, permission bits, block location, size etc.

回答2:

Namespace is nothing but a term we use to describe the tree structure of a filesystem.

Basically when we say namespace we mean a certain location on the hdfs.

‘/’ or ‘root’ dir is a namespace. The folder /user is a namespace. In Hadoop we refer to a Namespace as a dir which is handled by the NameNode.

ref:https://www.quora.com/What-is-%E2%80%98Namespace%E2%80%99-in-HDFS-and-what-would-be-the-contents-residing-in-a-%E2%80%98Namespace%E2%80%99