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Chapter: Distributed Systems - Peer To Peer Services and File System

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Global Name Service (GNS)

Designed and implemented by Lampson and colleagues at the DEC Systems Research Center (1986)

Global Name Service (GNS)

 

Designed and implemented by Lampson and colleagues at the DEC Systems Research Center (1986)

Provide facilities for resource location, email addressing and authentication

 

When the naming database grows from small to large scale, the structure of name space may change

 

the service should accommodate it

Cache consistency ?

The GNS manages a naming database that is composed of a tree of directories holding names and values. Directories are named by multi-part pathnames referred to a root, or relative to a working directory, much like file names in a UNIX file system. Each directory is also assigned an integer, which serves as a unique directory identifier (DI). A directory contains a list of names and references. The values stored at the leaves of the directory tree are organized into value trees, so that the attributes associated with names can be structured values.

 

Names in the GNS have two parts: <directory name, value name>. The first part identifies a directory; the second refers to a value tree, or some portion of a value tree.

 

GNS Structure

 

Tree of directories holding names and values

 

Muti-part pathnames refer to the root or relative working directory (like Unix file system)

 

Unique Directory Identifier (DI)

 

A directory contains list of names and references

 

Leaves of tree contain value trees (structured values)

GNS directory tree and value tree


Accommodating changes

 

How to integrate naming trees of two previously separate GNS services But what is for ‘/UK/AC/QMV, Peter.Smith’ ?


Using DI to solve changes

 

Using the name ‘#599/UK/AC/QMV, Peter.Smith’


Restructuring of database

 

Using symbolic links


 


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