OSF DCE Administration Guide--Core Components

OSF DCE Administration Guide—Core Components
information for CDS to store as attributes of a name. Then, when a client application
user refers to the resource by its CDS name, CDS retrieves data from the attributes for
use by the client application.
A system running CDS server software is a CDS server. A CDS server stores and
maintains CDS names and handles requests to create, modify, or look up data.
A component called the clerk is the interface between client applications and CDS
servers. Every DCE node must run a CDS clerk. The clerk receives a request from a
client application, sends the request to a server, and returns the resulting information to
the client. This process is called a lookup. The clerk is also the interface through which
client applications create and modify names. One clerk can work on behalf of many
client applications.
The clerk caches, or saves, the results of lookups so that it does not have to repeatedly go
to a server for the same information. The cache is written to disk periodically so that the
information can survive a system reboot or the restart of an application. When you stop
the CDS advertiser, the cache is written to disk. Caching improves performance and
reduces network traffic.
Figure 12-1 shows a sample configuration of CDS clerks and servers on a 9-node local
area network (LAN). Every node is a clerk, and CDS servers run on two selected nodes.
Figure 12-1. CDS Clerks and Servers on a LAN
ClerkClerk ClerkClerkServerClerk
Clerk Server Clerk ClerkClerk Clerk ClerkClerk ServerClerk
ServerClerk Clerk
Server
Server
Every CDS server has a database called a clearinghouse in which it stores names and
other CDS data. The clearinghouse is where a CDS server adds, modifies, deletes, and
retrieves data on behalf of client applications. Although more than one clearinghouse
can exist at a server node, it is not recommended as a normal configuration.
Figure 12-2 shows the interaction between a CDS client, clerk, server, and clearinghouse
during a simple lookup. It illustrates the following CDS lookup steps:
1. The client application on Node 1 sends a lookup request to the local clerk.
2. The clerk checks its cache and, not finding the name there, contacts the server on
Node 2.
3. The server checks to see if the name is in its clearinghouse.
4. The name exists in the clearinghouse, so the server gets the requested information.
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