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I'm learning hadoop and while studying am getting confused with two terms one Namespace and second is Metadata.

What I have studied so far about metadata is Metadata is a part of namenode server. Its about all the information of files in HDFS, replication factor, datanode's data blocks, file permissions etc. This metadata stores in a file called fsimage. Please correct me if am wrong

Second is Namespace, About namespace is the only thing I got know is Its just an folder structure and even am not sure about that. Could you guys share with me about these terms precisely ? I'm confused with the word Namespace itself..!!

And how it looks in Hadoop system and where I can see both these terms if I want to see in my local machine where I have installed hadoop ?

Nele
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  • Can you provide references where you found these terms? Metadata on the namenode is correct. FsImage, is a thing, yes. Namespace is not a term I've heard about – OneCricketeer Oct 15 '17 at 19:09
  • @cricket_007, I was reading from here https://hadoop.apache.org/docs/r1.2.1/hdfs_design.html#The+File+System+Namespace and https://stackoverflow.com/questions/23922878/what-is-the-meaning-of-namespace-and-metadata-which-were-used-in-hdfsnamenode but could not understand ..!! – Nele Oct 16 '17 at 03:05

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Seems like Namespace is just some HDFS Path, or some prefix against a Hive/HBase table to designate it amongst others.

Metadata holds information about namespaces just because it represents files. You seem to have gotten an understanding about the metadata information.

There isn't a difference, they are complimentary.

OneCricketeer
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Namespace contains directories and files which are listed in hierarchical order. Where as metadata is which contains the information like file permission,location,block ids,timestamp,file permissions etc.

Ajay Kumar Raj
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