Oracle Net

Connect descriptor

A connect descriptor consists of

the location of the listener that is accessed through a protocol address and
the service name of the database to which to connect.

tnsnames.ora

The tnsnames.ora contains the mappings

from network service names to connect descriptors (local naming method)
from net service names to listener protocol addresses

Oracle Net tries to find the tnsnames.ora in the following locations:

$TNS_ADMIN/tnsnames.ora
$ORACLE_BASE_HOME/network/admin/tnsnames.ora
$ORACLE_HOME/network/admin/tnsnames.ora

If the directory pointed at with the $TNS_ADMIN environment variable exists, but does contain have a tnsnames.ora file, the file is assumed to be missing and Oracle NET will not try to find it in other directories.

On Windows, Oracle also checks for a stated location in the registry.

Format of entries in tnsnames.ora

tnsnames.ora contains one or more entries in the following format:

NET_SERVICE_NAME = (
   DESCRIPTION = (
      ADDRESS=( protocol_address )
   )
   (  CONNECT_DATA = (
        SERVICE_NAME=service_name
      )
   )
)

The value if protocol_address is used to locate and contact the listener.

After the listener was contacted, the client passes the information in service_name to the listener which in turn will then try to locate and contact the specified Oracle service

The value of SERVICE_NAME corresponds to the global database name specified when the database was created.

The global database name is a combination of the database name and a domain name. For example, the global database name foodb.somewhere.xyz corresponds to the database name foodb and the domain name somewhere.xyz.

Leading blank spaces

MOS Note 730067.1 points out that ORA-01031: insufficient privileges may be thrown if the definition of SQLNET.AUTHENTICATION_SERVICES has leading blank spaces.

TODO: extproc_connection_data

Is extproc_connection_data used to call external procedures?

sqlnet.ora

Enable client tracing at support level:

TRACE_LEVEL_CLIENT      = 16
TRACE_FILE_CLIENT       = CLIENT
TRACE_DIRECTORY_CLIENT  = C:\Users\rene\oratrace
TRACE_TIMESTAMP_ CLIENT = ON
TRACE_UNIQUE_CLIENT     = ON
DIAG_ADR_ENABLED=OFF

Error messages

TNS-03505: Failed to resolve name	Unable to contact the listener specified in the `(DESCRIPTION…)` section of the connect descriptor.
ORA-12170: TNS:Connect timeout occurred
TNS-12541: TNS:no listener
ORA-12154: TNS: could not resolve the connect identifier specified	The listener could be contacted but it was unable to contect the service specified in the (`CONNECT_DATA…)` section
ORA-12514: TNS:listener does not currently know of service requested in connect descriptor	The listener could be contacted but it is not configured to handle the service specified in the `(CONNECT_DATA …)` seciton
ORA-12518: TNS:listener could not hand off client connection
ORA-12560: TNS:protocol adapter error
ORA-03135: connection lost contact

Performance

The only two parameters(?) that affect network throughput (and thus performance) are

Setting Session Data Unit (SDU)
Setting tcp.nodelay (which disable's Nagle's algorithm)

However, performance is indirectly affected by

Server load/Database performance
Network performance itself
If Shared Server (MTS) is used
If Shared Server (MTS) is used
Buffer size at TCP level