A package
is a container for related objects. It has specification and body. Each of them
is stored separately in data dictionary.
PACKAGE SYNTAX
Create or replace package <package_name> is
--
package specification includes subprograms signatures, cursors and global
or
public variables.
End <package_name>;
Create or replace package body <package_name> is
-- package body
includes body for all the subprograms declared in the spec, private
Variables and
cursors.
Begin
-- initialization
section
Exception
-- Exception
handling seciton
End <package_name>;
IMPORTANT POINGS ABOUT PACKAGES
Ø The first time a packaged subprogram is
called or any reference to a packaged variable or type is made, the package is
instantiated.
Ø Each session will have its own copy of
packaged variables, ensuring that two sessions executing subprograms in the
same package use different memory locations.
Ø In many cases initialization needs to be
run the first time the package is instantiated within a session. This can be
done by adding initialization section to the package body after all the
objects.
Ø Packages are stored in the data dictionary
and can not be local.
Ø Packaged subprograms has an advantage over
stand alone subprogram.
Ø When ever any reference to package, the
whole package p-code was stored in shared pool of SGA.
Ø Package may have local subprograms.
Ø You can include authid clause inside the
package spec not in the body.
Ø The execution section of a package is know
as initialization section.
Ø You can have an exception section at the
bottom of a package body.
Ø Packages subprograms are not invalidated.
COMPILING PACKAGES
Ø SQL> Alter package PKG compile;
Ø SQL> Alter package PKG compile specification;
Ø SQL> Alter package PKG compile body;
PACKAGE DEPENDENCIES
Ø The package body depends on the some
objects and the package header.
Ø The package header does not depend on the
package body, which is an advantage of packages.
Ø We can change the package body with out
changing the header.
Package runtime state is differ for the following packages.
Ø Serially reusable packages
Ø Non serially reusable packages
SERIALLY REUSABLE PACKAGES
To force the oracle to use serially reusable version then include PRAGMA SERIALLY_REUSABLE in both package spec and body, Examine the
following package.
CREATE OR REPLACE PACKAGE PKG IS
pragma serially_reusable;
procedure emp_proc;
END PKG;
CREATE OR REPLACE PACKAGE BODY PKG IS
pragma serially_reusable;
cursor c is select ename from
emp;
PROCEDURE EMP_PROC IS
v_ename emp.ename%type;
v_flag boolean := true;
v_numrows number := 0;
BEGIN
if not c%isopen then
open c;
end if;
while v_flag loop
fetch c into v_ename;
v_numrows := v_numrows + 1;
if v_numrows = 5 then
v_flag := false;
end if;
dbms_output.put_line('Ename = ' ||
v_ename);
end loop;
END EMP_PROC;
END PKG;
SQL> exec pkg.emp_proc
Ename = SMITH
Ename = ALLEN
Ename = WARD
Ename = JONES
Ename = MARTIN
SQL> exec pkg.emp_proc
Ename = SMITH
Ename = ALLEN
Ename = WARD
Ename = JONES
Ename = MARTIN
Ø The above package displays the same output
for each execution even though the cursor is not closed.
Ø Because the serially reusable version
resets the state of the cursor each time it was called.
NON SERIALL Y REUSABLE PACKAGES
This is the default version used by the oracle, examine the
following package.
CREATE OR REPLACE PACKAGE PKG IS
procedure emp_proc;
END PKG;
CREATE OR REPLACE PACKAGE BODY PKG IS
cursor c is select ename from
emp;
PROCEDURE EMP_PROC IS
v_ename emp.ename%type;
v_flag boolean := true;
v_numrows number := 0;
BEGIN
if not c%isopen then
open c;
end if;
while v_flag loop
fetch c into v_ename;
v_numrows := v_numrows + 1;
if v_numrows = 5 then
v_flag := false;
end if;
dbms_output.put_line('Ename = '
|| v_ename);
end loop;
END EMP_PROC;
END PKG;
SQL> exec pkg.emp_proc
Ename = SMITH
Ename = ALLEN
Ename = WARD
Ename = JONES
Ename = MARTIN
SQL> exec pkg.emp_proc
Ename = BLAKE
Ename = CLARK
Ename = SCOTT
Ename = KING
Ename = TURNER
Ø The above package displays the different
output for each execution even though the cursor is not closed.
Ø Because the non-serially reusable version
remains the state of the cursor over database calls.
DEPENDENCIES OF PACKAGE
RUNTIME STATE
Dependencies can exists between package state and anonymous
blocks.
Examine the following program
Create this package in first session
CREATE OR REPLACE PACKAGE PKG IS
v number := 5;
procedure p;
END PKG;
CREATE OR REPLACE PACKAGE BODY PKG IS
PROCEDURE P IS
BEGIN
dbms_output.put_line('v = ' || v);
v := 10;
dbms_output.put_line('v = ' || v);
END P;
END PKG;
Connect to second session, run the
following code.
BEGIN
pkg.p;
END;
The above code wil work.
Go back to first session and recreate the
package using create.
Then connect to second session and run the
following code again.
BEGIN
pkg.p;
END;
This above code will not work because of the following.
Ø The anonymous block depends on pkg. This is
compile time dependency.
Ø There is also a runtime dependency on the
packaged variables, since each session has its own copy of packaged variables.
Ø Thus when pkg is recompiled the runtime
dependency is followed, which invalidates the block and raises the oracle
error.
Ø Runtime dependencies exist only on package
state. This includes variables and cursors declared in a package.
Ø If the package had no global variables, the
second execution of the anonymous block would have succeeded.
PURITY LEVELS
In general, calls to subprograms are procedural, they cannot be
called from SQL statements. However, if a stand-alone or
packaged function meets certain restrictions, it can be called during execution
of a SQL statement.
User-defined functions are called the same way as built-in
functions but it must meet different restrictions. These restrictions are
defined in terms of purity levels.
There are four types of purity levels.
WNDS -- Writes No Database State
RNDS -- Reads No Database State
WNPS -- Writes NoPackage State
WNPS -- Writes No
RNPS -- Reads No Package State
In addition to the preceding restrictions, a user-defined function
must also meet the following requirements to be called from a SQL statement.
Ø The function has to be stored in the
database, either stand-alone or as part of a
package.
Ø The function can take only in parametes.
Ø The formal parameters must use only
database types, not PL/SQL types such as
boolean or record.
Ø The return type of the function must also
be a database type.
Ø The function must not end the current
transaction with commit or rollback, or
rollback to a savepoint prior to the function execution.
Ø It also must not issue any alter session or
alter system commands.
RESTRICT_REFERENCES
For packaged functions, however, the RESTRICT_REFERENCES pragma is required to specify the purity
level of a given function.
Syntax:
PRAGMA RESTRICT_REFERENCES(subprogram_name
or package_name, WNDS
[,WNPS]
[,RNDS] [,RNPS]);
Ex:
CREATE OR REPLACE PACKAGE PKG IS
function fun1 return varchar;
pragma
restrict_references(fun1,wnds);
function fun2 return varchar;
pragma
restrict_references(fun2,wnds);
END PKG;
CREATE OR REPLACE PACKAGE BODY PKG IS
FUNCTION FUN1 return varchar IS
BEGIN
update dept set deptno = 11;
return 'hello';
END FUN1;
FUNCTION
FUN2 return varchar IS
BEGIN
update dept set dname ='aa';
return 'hello';
END FUN2;
END PKG;
The above package body will not created, it will give the
following erros.
PLS-00452: Subprogram
'FUN1' violates its associated pragma
PLS-00452: Subprogram
'FUN2' violates its associated pragma
CREATE OR REPLACE PACKAGE BODY PKG IS
FUNCTION FUN1 return varchar IS
BEGIN
return 'hello';
END FUN1;
FUNCTION
FUN2 return varchar IS
BEGIN
return 'hello';
END FUN2;
END PKG;
Now the package body will be created.
DEFAULT
If there is no RESTRICT_REFERENCES pragma associated with a given packaged
function, it will not have any purity level asserted. However, you can change
the default purity level for a package. The DEFAULT
keyword is used instead of the subprogram name in the pragma.
Ex:
CREATE OR REPLACE PACKAGE PKG IS
pragma
restrict_references(default,wnds);
function fun1 return varchar;
function fun2 return varchar;
END PKG;
CREATE OR REPLACE PACKAGE BODY PKG IS
FUNCTION FUN1 return varchar IS
BEGIN
update dept set deptno = 11;
return 'hello';
END FUN1;
FUNCTION
FUN2 return varchar IS
BEGIN
update dept set dname ='aa';
return 'hello';
END FUN2;
END PKG;
The above package body will not created, it will give the
following erros because the pragma will apply to all the functions.
PLS-00452: Subprogram
'FUN1' violates its associated pragma
PLS-00452: Subprogram
'FUN2' violates its associated pragma
CREATE OR REPLACE PACKAGE BODY PKG IS
FUNCTION FUN1 return varchar IS
BEGIN
return 'hello';
END FUN1;
FUNCTION
FUN2 return varchar IS
BEGIN
return 'hello';
END FUN2;
END PKG;
Now the package body will be created.
TRUST
If the TRUST keyword is present, the restrictions
listed in the pragma are not enforced. Rather, they are trusted to be true.
Ex:
CREATE OR REPLACE PACKAGE PKG IS
function fun1 return varchar;
pragma
restrict_references(fun1,wnds,trust);
function fun2 return varchar;
pragma
restrict_references(fun2,wnds,trust);
END PKG;
CREATE OR REPLACE PACKAGE BODY PKG IS
FUNCTION FUN1 return varchar IS
BEGIN
update dept set deptno = 11;
return 'hello';
END FUN1;
FUNCTION
FUN2 return varchar IS
BEGIN
update dept set dname ='aa';
return 'hello';
END FUN2;
END PKG;
The above package will be created successfully.
IMPORTANT POINTS ABOUT RESTRICT_REFERENCES
Ø This pragma can appear anywhere in the
package specification, after the function
declaration.
Ø It can apply to only one function
definition.
Ø For overload functions, the pragma applies
to the nearest definition prior to the
Pragma.
Ø This pragma is required only for packages
functions not for stand-alone functions.
Ø The Pragma can be declared only inside the
package specification.
Ø The pragma is checked at compile time, not
runtime.
Ø It is possible to specify without any
purity levels when trust or combination of
default and trust keywords are present.
PINNING IN THE SHARED POOL
The shared pool is the
portion of the SGS that contains, among other things, the p-code of compiled
subprograms as they are run. The first time a stored a store subprogram is
called, the p-code is loaded from disk into the shared pool. Once the object is
no longer referenced, it is free to be aged out. Objects are aged out of the
shared pool using an LRU(Least Recently Used) algorithm.
The DBMS_SHARED_POOL package allows you to pin objects in the
shared pool. When an object is pinned, it will never be aged out until you
request it, no matter how full the pool gets or how often the object is
accessed. This can improve performance, as it takes time to reload a package
from disk.
DBMS_SHARED_POOL has
four procedures
Ø KEEP
Ø UNKEEP
Ø SIZES
Ø ABORTED_REQUEST_THRESHOLD
KEEP
The DBMS_SHARED_POOL.KEEP procedure is used to pin objects in the
pool.
Syntax:
PROCEDURE KEEP(object_name
varchar2,flag char default ‘P’);
Here the flag represents different types of flag values for
different types of objects.
P -- Package, function or procedure
Q -- Sequence
R -- Trigger
C -- SQL Cursor
T -- Object type
JS -- Java source
JC -- Java class
JR -- Java resource
JD -- Java shared data
UNKEEP
UNKEEP is the
only way to remove a kept object from the shared pool, without restarting the
database. Kept objects are never aged out automatically.
Syntax:
PROCEDURE UNKEEP(object_name
varchar2, flag char default ‘P’);
SIZES
SIZES will
echo the contents of the shared pool to the screen.
Syntax:
PROCEDURE SIZES(minsize
number);
Objects with greater than the minsize
will be returned. SIZES uses DBMS_OUTPUT to
return the data.
ABORTED_REQUEST_THRESHOLD
When the database determines that there is not enough memory in
the shared pool to satisfy a given request, it will begin aging objects out
until there is enough memory. It enough objects are aged out, this can have a
performance impact on other database sessions. The ABORTED_REQUEST_THRESHOLD can be used to remedy this.
Syntax:
PROCEDURE ABORTED_REQUEST_THRESHOLD(threshold_size
number);
Once this procedure is called, oracle will not start aging objects
from the pool unless at least threshold_size
bytes is needed.
DATA MODEL FOR SUBPROGRAMS AND PACKAGES
Ø USER_OBJECTS
Ø USER_SOURCE
Ø USER_ERRORS
Ø DBA_OBJECTS
Ø DBA_SOURCE
Ø DBA_ERRORS
Ø ALL_OBJECTS
Ø ALL_SOURCE
Ø ALL_ERRORS
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