Oracle Features of SQL*Net version 1
When a connection is made to SQL*Net, it
passes the request to its underlying layer, the TNS, where the
request is transmitted to the appropriate server. At the
server, SQL*Net receives the request from TNS and passes the SQL
to the database. TNS is the “transparent network substrate”; a
single, common interface to all protocols. TNS has the ability
to connect to databases in physically separate networks. At the
lowest level, TNS communicates to other databases with message
level send-receive commands.
Client side - The User Programmatic
Interface (UPI) is the central client component. The UPI
converts SQL to associated parse, execute and fetch statements.
The UPI parses the SQL, opens the SQL cursor, binds the client
application, describes the contents of returned data fields,
executes the SQL, fetches the rows and closes the cursor.
Oracle attempts to minimize messages to the server by combining
UPI calls whenever possible.
Server side - The Oracle Programmatic
Interface (OPI) is the central server component. The OPI is the
obverse of the UPI; it responds to all possible messages from
the UPI and returning requests.
For server to server communication there
is no UPI, instead there is a Network Programmatic Interface (NPI)
at the initiating server. SQL*Net supports network transparency
such that the network structure may be changed without effecting
the SQL*Net application. Location transparency is achieved with
database-links and synonyms.
SQL*Net v 1 was the first attempt by
Oracle at database connectivity. In SQL*Net v 1, database
connections requires that the request supply all of the
connection information. This includes the protocol, the host
name (or IP address) and the database name. To connect to the
“tom” database on the dilbert server using TCP/IP, you would set
a UNIX environment variable called TWO_TASK. When the request
is made SQL*Net v 1 will interrogate the contents of TWO_TASK to
get the database information.
For example, let’s make a connection
from the fred server to the dilbert server, and connect to the
“tom” databases using TCP/IP:
Fred> export TWO_TASK=t:dilbert:tom
fred> sqlplus /
SQL*Plus: Release 184.108.40.206.0 - Production
on Thu Mar 18 08:25:30 1999
Copyright (c) Oracle Corporation 1979,
1996. All rights reserved.
Oracle7 Server Release 220.127.116.11.0 -
With the distributed option
PL/SQL Release 18.104.22.168.0 - Production
SQL> select * from v$database;
NAME CREATED LOG_MODE
------------ ------------------ ---------------
TOM 06/13/98 19:00:26
NOARCHIVELOG 2.8713E+12 2.8713E+12
One of the biggest shortcoming of
SQL*Net v 1 was the requirement to “know” all of the connection
information, instead of having a look-up file to get this
information. In SQL*Net version 2 we see this information.