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1) PRAGMA SERIALLY_REUSABLE for Package

1@@@@Serializable Packages (PRAGMA SERIALLY_REUSABLE)

As you have seen, package data by default persists for your entire session (or until the

package is recompiled). This is an incredibly handy feature, but it has some drawbacks:

~ Globally accessible (public and private) data structures persist, and that can cause

undesired side effects. In particular, I can inadvertently leave packaged cursors

open, causing ¡°already openâ?? errors in other programs.

~ My programs can suck up lots of real memory (package data is managed in the

user¡¯s memory area or User Global Area [UGA]) and then not release it if that data

is stored in a package-level structure.

To help you manage the use of memory in packages, PL/SQL offers the

SERIALLY_REUSABLE pragma. This pragma, which must appear in both the package

specification and the body (if one exists), marks that package as serially reusable. For

such packages, the duration of package state (the values of variables, the open status

of a packaged cursor, etc.) can be reduced from a whole session to a single call of a

program in the package.

@@@Example01: Test with PRAGMA SERIALLY_REUSABLE

SYS@ocm> !cat tmp.sql

DROP TABLE books

/

CREATE TABLE books

( author VARCHAR2(100)

, title VARCHAR2(250)

, page_count NUMBER(5)

, CONSTRAINT pk_books PRIMARY KEY (author, title) )

/

BEGIN

DELETE FROM books;

INSERT INTO books VALUES('fatpander_small_one','Pander Trveral', 100);

INSERT INTO books VALUES('fatpander_big_one','Pander Trveral', 100);

COMMIT;

END;

/

CREATE OR REPLACE PACKAGE book_info

IS

PRAGMA SERIALLY_REUSABLE;

PROCEDURE fill_list;

PROCEDURE show_list;

END;

/

CREATE OR REPLACE PACKAGE BODY book_info

IS

PRAGMA SERIALLY_REUSABLE;

TYPE book_list_aat IS TABLE OF books%ROWTYPE

INDEX BY PLS_INTEGER;

my_books_aa book_list_aat;

PROCEDURE fill_list

IS

BEGIN

FOR rec IN (SELECT *

FROM books

WHERE author LIKE '%big%')

LOOP

my_books_aa (my_books_aa.COUNT+1) := rec;

END LOOP;

END fill_list;

PROCEDURE show_list

IS

BEGIN

IF my_books_aa.COUNT = 0

THEN

DBMS_OUTPUT.put_line('** Associate array my_books_at is empty');

ELSE

FOR i IN 1 .. my_books_aa.COUNT

LOOP

DBMS_OUTPUT.put_line( my_books_aa(i).title );

END LOOP;

END IF;

END;

END;

/

SYS@ocm> @tmp.sql

Table dropped.

Table created.

PL/SQL procedure successfully completed.

Package created.

Package body created.

SYS@ocm>

@@@ Begin to test, run the package procedure together

SYS@ocm> !cat test_together.sql

BEGIN

DBMS_OUTPUT.put_line('Fill and show in same block:');

book_info.fill_list;

book_info.show_list;

END;

/

SYS@ocm> @test_together.sql

Fill and show in same block:

Pander Trveral ------------Here exist

PL/SQL procedure successfully completed.

@@@ Begin to test, run the package procedure seprately

SYS@ocm> !cat test_seprate01.sql

BEGIN

DBMS_OUTPUT.put_line('Fill in first block');

book_info.fill_list;

END;

/

SYS@ocm> !cat test_seprate02.sql

BEGIN

DBMS_OUTPUT.put_line('Show in seond block');

book_info.show_list;

END;

/

SYS@ocm> @test_seprate01.sql

Fill in first block

PL/SQL procedure successfully completed.

SYS@ocm> @test_seprate02.sql

Show in seond block

** Associate array my_books_at is empty -----Not exist

PL/SQL procedure successfully completed.

@@@Versus Example01 and Example02

@@@Example02: Test without PRAGMA SERIALLY_REUSABLE

CREATE OR REPLACE PACKAGE book_info

IS

PROCEDURE fill_list;

PROCEDURE show_list;

END;

/

CREATE OR REPLACE PACKAGE BODY book_info

IS

TYPE book_list_aat IS TABLE OF books%ROWTYPE

INDEX BY PLS_INTEGER;

my_books_aa book_list_aat;

PROCEDURE fill_list

IS

BEGIN

FOR rec IN (SELECT *

FROM books

WHERE author LIKE '%big%')

LOOP

my_books_aa (my_books_aa.COUNT+1) := rec;

END LOOP;

END fill_list;

PROCEDURE show_list

IS

BEGIN

IF my_books_aa.COUNT = 0

THEN

DBMS_OUTPUT.put_line('** Associate array my_books_at is empty');

ELSE

FOR i IN 1 .. my_books_aa.COUNT

LOOP

DBMS_OUTPUT.put_line( my_books_aa(i).title );

END LOOP;

END IF;

END;

END;

/

@@@Test code the same above Example01

SYS@ocm> @test_together.sql

Fill and show in same block:

Pander Trveral

PL/SQL procedure successfully completed.

SYS@ocm> @test_seprate01.sql

Fill in first block

PL/SQL procedure successfully completed.

SYS@ocm> @test_seprate02.sql

Show in seond block

Pander Trveral ------------------Here Exist

Pander Trveral ------------------Here Exist

PL/SQL procedure successfully completed.

@@@Summary: package with PRAGMA SERIALLY_REUSABLE could save memory.

Here are some things to keep in mind for serialized packages:

~ The global memory for serialized packages is allocated in the SGA, not in the user¡¯s

UGA. This approach allows the package work area to be reused. Each time the

package is reused, its package-level variables are initialized to their default values

or to NULL, and its initialization section is re-executed.

~ The maximum number of work areas needed for a serialized package is the number

of concurrent users of that package. The increased use of SGA memory is offset by

the decreased use of UGA or program memory. Finally, the database ages out work

areas not in use if it needs to reclaim memory from the SGA for other requests.

referencing "Oracle PL/SQL Program Design 5th Edition"
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