Network Services

Oracle features an active background process called a 'Listener' which can be configured through listener.ora found at the default location $ORACLE_HOME/network/admin/

A service request packet is sent from the client to the address specified in the calling clientsTNSNAMES.ORA file. If a listener exists at the destination address, the listener searches through its own list of available services and if the requested service is valid, the LISTENER spawns a server process to handle the request from there on. The server process proceeds to authenticate the call, pass on parameters and spawn a oracle session for the calling client.

From here on, the server process acts as the clients agent on the server by performing:
-SQL Parsing
-Checking the DB Buffer cache for blocks required to perform actions
-Reading data blocks from data files
-Managing Sorting
-Returning results to the user process
-Reading auditing options and reporting