Differences between listener. ora sqlnet. ora tnsnames. ora in Oracle databases

The listener. ora, sqlnet. ora, and tnsnames. ora configuration files are stored in the $ ORACLE_HOME \ network \ admin directory.
 
1. sqlnet. ora ----- is similar to the nsswitch. conf file of linux or other unix. It is used to determine how to find a connection string that appears in the connection.
For example, we enter
Sqlplus sys/oracle @ orcl
Assume that my sqlnet. ora is like the following:
SQLNET. AUTHENTICATION_SERVICES = (CNT)
NAMES. DIRECTORY_PATH = (TNSNAMES, HOSTNAME)
Then, the client will first be in tnsnames. orcl records in the ora file. if there is no corresponding record, try to use orcl as a host name, resolve its ip address through the network, and then connect to the instance GLOBAL_DBNAME = orcl on this ip address, of course, here, orcl is not a host name.
If I look like this
NAMES. DIRECTORY_PATH = (TNSNAMES)
Then the client will only search for orcl records from tnsnames. ora. There are other options in brackets, such as LDAP, which are not commonly used.
 
2. Tnsnames. ora ------ this file is similar to the unix hosts file. It provides the corresponding tnsname to the host name or ip address, only when sqlnet. ora is similar
NAMES. DIRECTORY_PATH = (TNSNAMES), that is, the client will try to use this file only when TNSNAMES is in the order in which the client parses the connection string.
PROTOCOL: the PROTOCOL for communications between the client and the server, which is generally TCP.
HOST: The name or IP address of the machine on which the database listens. The database listens on the same machine as the database, so when I say that the machine where the database listens is generally the machine where the database is located. In UNIX or WINDOWS, you can use the hostname command at the command prompt of the machine on which the database listens, or use ipconfig (for WINDOWS) or ifconfig (for UNIX) command to obtain the IP address. Note that, whether using the machine name or IP address, you must ping the Host Name of the machine where the database is listening on the client, otherwise, the host name of the machine where the database listening is located must be added to the hosts file.
PORT: the PORT on which the database listens. You can view the listener. ora file on the server or run the lnsrctl status [listener name] command at the command prompt on the machine where the database listens. The Port value must be the same as the Port on which the database listens.
SERVICE_NAME: on the server side, run the "sqlplus> show parameter service_name" command after logging on to the system.
ORCL: Another IP address corresponding to the local machine and SALES, which also defines whether to use the master server or Shared Server Mode for connection.
# TNSNAME entered during connection
ORCL =
(DESCRIPTION =
(ADDRESS_LIST =
# The host, port, and Protocol corresponding to this TNSNAME
(ADDRESS = (PROTOCOL = TCP) (HOST = 127.0.0.1) (PORT = 1521 ))
)
(CONNECT_DATA =
# The dedicated server mode must match the server mode to connect. If not, it is automatically adjusted according to the server mode.
(SERVER = DEDICATED)
# View the corresponding service_name, SQLPLUS>; show parameter service_name;
(SERVICE_NAME = orcl)
)
)
# The following is similar
SALES =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP) (HOST = dg1) (PORT = 1521 ))
)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = sales)
)
)
Note: If the database server uses MTS, it is best to explicitly specify the dedicated direct connection mode when the client program needs to use database link. Otherwise, there will be many ORACLE bugs related to the distributed environment. Generally, direct connection to the database server is better, unless your real-time database connection is close to 1000.
 
3. listener. ora ------ listener process configuration file
The listener process is not much said. The listener process accepts remote database access requests and transfers them to the oracle server process. Therefore, if you do not use a remote connection and do not need to use an OEM, the listener process is not necessary. Similarly, If you disable the listener process, the existing database connection will not be affected.
Example of Listener. ora File
# Listener. ora Network Configuration File: # E: \ oracle \ product \ 10.1.0 \ Db_2 \ NETWORK \ ADMIN \ listener. ora
# Generated by Oracle configuration tools.
# The following defines the instance for which the LISTENER process provides the service. Here it is ORCL, And it corresponds to ORACLE_HOME and GLOBAL_DBNAME. GLOBAL_DBNAME is not required unless
# Using HOSTNAME for database connection
SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(GLOBAL_DBNAME = boway)
(ORACLE_HOME =/u01/app/oracle)
(SID_NAME = ORCL)
)
)
# Listener name. A database can have more than one listener.
# Next we will talk to the listener about the protocol, ip address, port, etc. Here we use the tcp1521 port and use the # Host Name
LISTENER =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP) (HOST = dg1) (PORT = 1521 ))
)
The above example is the simplest, but also the most common. A listener process provides services for an instance (SID.
Listener Operation Command
$ ORACLE_HOME/bin/lsnrctl start, others such as stop and status. After you have typed an lsnrctl, you can view the help information.
 
The three files mentioned above can be configured through the graphical Configuration tool.
$ ORACLE_HOME/netca wizard
The profile is configured with sqlnet. ora, that is, the name resolution method.
The service name is configured with the tnsnames. ora file.
Listeners configures the listener. ora file, that is, the listener process.

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