What are libraries in Database?

Question

Hi All,
Recently i was going through objects in my database and i came across libraries
eg: dbms_trigger_lib, dbms_stats_lib etc.
I am not sure what role these libraries play and whether these are used for internal processing or can be used for development as well.
Can anyone give some information on this ?
Thanks
Amit

Answer 1

Libraries are alias from the Oracle Server Side to an external library in the OS. It is used with the Use Of External Libraries example:
You must build an external library, declare it as a LIBRARY object inside Oracle, configure your lib paths, and configure your listener.
Once you've met the config procedures, next you have to create a wrap function to access your external funcion inside a PLSQL block.
Check this documents:
http://download-west.oracle.com/docs/cd/B19306_01/appdev.102/b14289/dcimethcj.htm#sthref250
http://download-west.oracle.com/docs/cd/B19306_01/server.102/b15658/ldr_demo.htm#sthref565
http://download-west.oracle.com/docs/cd/B19306_01/server.102/b14231/manproc.htm#ADMIN00501
Step 1 - Make entry in the TNSNAMES.ORA.
======
Make the following entry in the TNSNAMES.ORA:
extproc_connection_data.world =
(DESCRIPTION =
(ADDRESS =
(PROTOCOL = IPC)
(KEY = extproc))
(CONNECT_DATA =
(SID = extproc)
Step 2 - Make the necessary entries in the LISTENER.ORA.
======
You can either add an entry to the existing listener or add another listener
process.
Option 1: Add an Entry to the Existing Listener
The information contained in each listener differs. Defining the
listener process is done in two parts. The first part is as follows:
LISTENER =
(ADDRESS_LIST =
(ADDRESS=
(PROTOCOL= IPC)
(KEY= V803)
(ADDRESS= <-Add this line.
(PROTOCOL= IPC) <-Add this line.
(KEY= extproc) <-Add this line.
(ADDRESS=
(PROTOCOL= TCP)
(Host= ###.#.#.#)
(Port= ####)
Step 3 - Start the listener process.
======
Any modifications to the existing listener require that you stop and
restart the listener to reload the new listener configuration. Adding a
second listener process, instead of modifying the current, only requires
the startup of the new listener process.
Step 4 - Create a sample DLL using the following code.
======
The following is a basic example of an external procedure. It is a good
way to test to ensure that the environment (mainly the listener) is configured
correctly.
Note: For the remaining steps, the DLL name should be MYEXTPROC.DLL.
#include <stdio.h>
int __declspec(dllexport) square(int x)
return(x*x);
Step 5 - Move the DLL to same server where the database is located.
======
The DLL can be placed in any directory. One approach would be to create an
EXTPROC directory under the ORACLE_HOME and use this to house all external
procedures.
Step 6 - Create the required library.
=======
Log into SQL*Plus and create a library to be associated with the external
procedure.
Note: The user must have CREATE LIBRARY privileges.
CREATE LIBRARY <mylib> AS <path\filename>;
SQL> CREATE LIBRARY SQUARE_LIB AS 'D:\ORANT\EXTPROC\MYEXTPROC.DLL';
Step 7 - Register the external procedure.
======
An external procedure is not called directly. Instead, you call the PL/SQL
subprogram that registers the external procedure. This can either be a
Function or a Stored Procedure.
CREATE OR REPLACE FUNCTION <FunctionName> (<parm1>...) RETURN <value> AS
EXTERNAL LIBRARY <mylib>
NAME "<Name Of Function In DLL>"
LANGUAGE C;
CREATE OR REPLACE PROCEDURE <ProcedureName> (<parm1>...) AS
EXTERNAL LIBRARY <mylib>
NAME "<Name Of Function In DLL>"
LANGUAGE C;
CREATE OR REPLACE FUNCTION square_of (X BINARY_INTEGER)
RETURN BINARY_INTEGER AS
EXTERNAL LIBRARY SQUARE_LIB
NAME "square"
LANGUAGE C;
Step 8 - Run the external procedure.
======
Use the following code to execute the external procedure:
CREATE OR REPLACE PROCEDURE EXTPROCTEST (X BINARY_INTEGER) AS
RetValue BINARY_INTEGER;
BEGIN
RetValue := square_of(X);
DBMS_OUTPUT.PUT_LINE(RetValue);
End;
EXECUTE EXTPROCTEST(15);