Create tnsnames.ora

Question:  I have just finished installing Oracle.  I want to update my tnsnames.ora file, but I cannot find a tnsnames.ora file on my system.  I thought the tnsnames.ora file would be created when I created the database.  How do I create the tnsnames.ora? 

Answer:   The tnsnames.ora is a SQL*Net configuration file that normally resides in the ORACLE_HOME/network/admin directory.  Specifically, the tnsnames.ora defines databases addresses so that connections can be made to them.

The creation of the database itself will not necessarily create the tnsnames.ora.  It is created along with the sqlnet.ora and listener.ora as part of the network configuration. Normally, the Network Configuration Assistant (NETCA) is started at the end of the installation process; however, if NETCA fails or you exit before completing, the tnsnames.ora and the other files will not be created.  The tnsnames.ora and the other  NETCA created files are not necessary for connecting to the database locally from the server.  They are just for client access, so it is possible for the database to be created properly and the files not exist. The tnsnames.ora file is located on both the client and server systems, but there will be only one tnsnames.ora on each server regardless of how many database instances exist.

If you have run NETCA and cannot locate the tnsnames.ora file, check to see if the tns_admin  parameter has been set to specify a different directory.  If you have not run NETCA, do so to create the tnsnames.ora file.

The easiest way for experienced users to edit the tnsnames.ora file is by using a text editor to manually update the file; however, the SQL*Net Easy Configurator GUI can also be used.  It has wizards the help guide users through the process of configuring as many connections as they want.

The basic format of the tnsnames.ora file is:

net_service_name=
  (description=
     (address=(protocol_address_information))
  (connect_data=
     (service_name=service_name)))

A sample tnsnames.ora entry might look like the following:

 ORATST=
 (description=
   (address_list=
     (address = (protocol = TCP)(host = fu.bar)(port = 1521))
   )
 (connect_data =
   (service_name=oratst)
 )
)

Where the following parameters are used:

• description:  This tnsnames.ora parameter acts as a container for a connect descriptor.  It can be embedded under the description_list parameter in the tnsnames.ora file.

• description_list:  This tnsnames.ora parameter defines a list of connect descriptors for a particular net service name .

• address: This tnsnames.ora parameter defines a single listener protocol address.  It can be embedded under the address_list or description parameters in the tnsnames.ora file.

• address_list:  This tnsnames.ora parameter defines multiple listener protocol addresses.  It is not necessary if only one listener protocol address is used.  It can be embedded under the description or description_list parameters in the tnsnames.ora file.

For multiple addresses, the following description section parameters are also available for the tnsnames.ora file:

• enable: Set to BROKEN to enable keepalive feature on the supported TCP transports. By default, the keepalive feature is OFF>

• failover:  Use this parameter to enable or disable connect-time failover for multiple protocol addresses. Setting the parameter to ON, YES or TRUE will result in Oracle Net, at connect time, failing over to a different address if the first protocol address fails. Setting the parameter to OFF, NO or FALSE will result in  Oracle Net trying only one protocol address. The default is ON for descriptions, description_lists and address_lists.

• load_balance:  Use this parameter to enable or disable client load balancing for multiple protocol addresses. Setting the parameter to ON, YES or TRUE causes the Oracle Net to progress through the list of addresses in a random sequence, balancing the load on the various listener or Oracle Connection Manager protocol addresses.   Setting the parameter to OFF, NO or FALSE will result in  Oracle Net sequentially trying the protocol addresses until one works. The default is ON for description_lists.

• recv_buf_size:  Use this parameter, supported by TCP/IP, TCP/IP with SSL and SDP protocols, to specify, in bytes, the buffer space for receive operations of sessions.  The default for this parameter is OS specific.

• sdu:  Use this parameter in the connect descriptor, embedded under the description parameter, on a client to override the default_sdu_size parameter in the client-side sqlnet.ora file in order to optimize the transfer rate of data packages across the network.  The default setting is 8192 (8 KB), and the available range is 512 to 32767 bytes.

• send_buf_size:  Use this parameter in the connect descriptor, embedded under the description parameter, on a client to override the send_buf_size parameter in the client-side sqlnet.ora file.    This parameter, supported by TCP/IP, TCP/IP with SSL and SDP protocols, specifies, in bytes, the buffer space for send operations of sessions.  The default for this parameter is OS specific.

• source_route:  Set the source_route parameter to ON or YES to enable routing through multiple protocol addresses in the specified order until the destination has been reached. This parameter can be embedded under the description, description_list or address_list parameter.  The default setting is OFF.

More information on tnsnames.ora is available HERE.

Also see the additional information on creating and editing listener.ora and sqlnet.ora.

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