7. Troubleshooting Connectivity
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Troubleshooting Connectivity
How Connection Between the Application and DBMS Server Is Established
For queries to be processed, applications must establish a connection to the DBMS Server through Ingres Net. When an application issues a query, the query is sent to the DBMS Server for execution. The server executes the query and returns data to the application.
For a client to connect to a server through Ingres Net, many internal connections must be made.
When the application, the DBMS Server, and the database reside on the same instance, establishing a connection is a short process:
1. The application program connects to the local Name Server (iigcn) and requests the listen address of the local DBMS Server process.
2. The Name Server returns this information to the application, which thereafter communicates directly with the DBMS Server through that address.
When the application and DBMS Server are on separate instances, the process has more steps:
1. The application finds the local Name Server (iigcn) listen address and talks to the local Name Server to request remote access.
2. The local Name Server passes the listen address of the local Communications Server (iigcc) and the listen address of the remote Communications Server (iigcc) back to the application. (The local Name Server (iigcn) stored the remote Communications server’s listen address when you ran netutil on the local instance.)
3. The application connects to the local Communications Server, passing it the remote Communications Server’s listen address as part of the remote access request.
4. The local Communications Server connects to the remote Communications Server and requests a connection to a DBMS Server on that remote instance.
5. The Communications Server on the remote instance finds the listen address of the Name Server on the remote instance. The Communications Server requests connection information from the Name Server, passing the name of the database for which a connection is requested.
6. The remote Name Server returns the listen address of a DBMS Server that is capable of servicing a request for connection to the target database.
7. The remote Communications Server connects to the DBMS Server on the remote instance.
When these steps are completed, a “virtual connection” has been established between the application and the DBMS Server.