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Lesson 7 The sqlnet.ora file, part 1
Objective Describe the location and general use of the sqlnet.ora file.

sqlnet.ora File Location

The basic purpose of the sqlnet.ora file is to provide server-specific information about default locations and thresholds for Net. The sqlnet.ora file is created for all Oracle servers and nodes on the network and includes the following information:
  1. The time interval between the sending of two probes to determine whether a client/server connection is still alive (This is called dead connection detection.)
  2. Optional tracing and logging parameters
  3. Client parameters for use with Oracle Names
  4. The location of the Net trace and log files
  5. Other optional parameters
In Oracle7, the default location of sqlnet.ora is in the $ORACLE_HOME/network/admin directory on a UNIX server, and in ORACLE_HOME\network\admin on Windows servers.
In the next lesson, we will look at a sqlnet.ora file for an Oracle server.

1) The settings in the sqlnet.ora file apply to all pluggable databases (PDBs) in a multitenant container database environment.
2) Oracle Net Services supports the IFILE parameter in the sqlnet.ora file, with up to three levels of nesting. The parameter is added manually to the file. The following is an example of the syntax: 
IFILE=/tmp/listener_em.ora
IFILE=/tmp/listener_cust1.ora
IFILE=/tmp/listener_cust2.ora

Refer to Oracle Database Reference for additional information. 3)In the read-only Oracle home mode,, the sqlnet.ora file default location is ORACLE_BASE_HOME/network/admin.
4) In the read-only Oracle home mode, the parameters that default to ORACLE_HOME location change to default to ORACLE_BASE_HOME location.

Dead Connection Detection

Note: The following paragraph was for the legacy Oracle Network technology SQL*Net/Net which has been replaced with Oracle Network Services.
SQL*Net/Net can automatically detect and terminate connections that are no longer valid. This feature is particularly useful for environments in which the clients are PCs, because users may reboot their PCs or otherwise terminate their sessions without logging out of the database. Rebooting a PC does not in and of itself cause the corresponding database session to terminate, because the underlying transport, such as TCP/IP, does not recognize it as such. The worst-case scenario is that the user reboots his PC while he has a lock on a table. Although you can assign a profile to your users that limits connect time and idle time, you usually have to set these limits high enough to accommodate users who want to go out to lunch without logging out of the application (e.g., several hours). You can use dead connection detection to search and destroy invalid connections every 10 minutes or so. To do so, you must specify the optional parameter SQLNET.EXPIRE_TIME in the sqlnet.ora file. The number you specify is the frequency in minutes with which SQL*Net/Net probes connections to confirm their validity. Sessions that are dead or invalid are terminated. If dead connection detection is enabled, SQL*Net sends a probe periodically to determine whether there is an invalid connection that should be terminated. If it finds a dead connection, or a connection that returns an error, it causes the server to terminate the connection.
Of course, there is a certain amount of overhead associated with using dead connection detection:
  1. Additional network traffic for the dead connection probes every SQLNET.EXPIRE_TIME minutes.
  2. Potential performance degradation on the Oracle server which must distinguish between connection probing events and other events. You should perform your own analysis to determine whether your platform is adversely affected.
Some protocols have their own dead connection detection algorithms, which may obviate the need to use SQL*Net/Net's version.