Release 8.0
A58241-01
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| Oracle8 Application Developer's Guide Release 8.0 A58241-01 |
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The definitions of certain schema objects, such as views and procedures, reference other schema objects, such as tables. Therefore, some schema objects are dependent upon the objects referenced in their definitions. This chapter discusses how to manage the dependencies among schema objects. Topics include the following:
When you create a stored procedure or function, Oracle verifies that the operations it performs are possible based on the schema objects accessed. For example, if a stored procedure contains a SELECT statement that selects columns from a table, Oracle verifies that the table exists and contains the specified columns. If the table is subsequently redefined so that one of its columns does not exist, the stored procedure may not work properly. For this reason, the stored procedure is said to depend on the table.
In cases such as this, Oracle automatically manages dependencies among schema objects. After a schema object is redefined, Oracle automatically recompiles all stored procedures and functions in your database that depend on the redefined object the next time they are called. This recompilation allows Oracle to verify that the procedures and functions can still execute properly based on the newly defined object.
Runtime recompilation reduces runtime performance and the possible resulting runtime compilation errors can halt your applications. Follow these measures to avoid runtime recompilation:
You can manually recompile a procedure, stored function, or package with the COMPILE option of the ALTER PROCEDURE, ALTER FUNCTION, or ALTER PACKAGE command.
You can determine the dependencies among the schema objects in your database by running the SQL script UTLDTREE.SQL.
There are several dependency issues to consider before dropping a procedure or package. Additional information about dependency issues is included in Oracle8 Concepts. Some guidelines for managing dependencies follow.
Packages are the most effective way of preventing unnecessary dependency checks from being performed. The following example illustrates this benefit.
Assume this situation:
PROC depends on a packaged procedure PACK_PROC.
PACK_PROC procedure's definition is altered by recompilation of the package body.
PACK_PROC procedure's specification is not altered in the package specification.
Even though the package's body is recompiled, the stand-alone procedure PROC that depends on the packaged procedure PACK_PROC is not invalidated, because the package's specification is not altered.
This technique is especially useful in distributed environments. If procedures are always part of a package, remote procedures that depend on packaged procedures are never invalidated unless a package specification is replaced or invalidated.
Whenever you recompile a procedure, you should consult with any other database administrators and application developers to identify any remote, dependent procedures and ensure that they are also recompiled. This eliminates recompilations at runtime and allows you to detect any compile-time errors that would otherwise be seen by the application user.
The %TYPE attribute provides the datatype of a variable, constant, or column. This attribute is particularly useful when declaring a variable or procedure argument that refers to a column in a database table. The %ROWTYPE attribute is useful if you want to declare a variable to be a record that has the same structure as a row in a table or view, or a row that is returned by a fetch from a cursor.
When you declare a construct using %TYPE and %ROWTYPE, you do not need to know the datatype of a column or structure of a table. For example, the argument list of a procedure that inserts a row into the EMP table could be declared as
CREATE PROCEDURE hire_fire(emp_record emp%ROWTYPE) AS ... END;
If you change the column or table structure, the constructs defined on their datatypes or structure automatically change accordingly.
However, while one type of dependency is eliminated using %TYPE or %ROWTYPE, another is created. If you define a construct using object%TYPE or object%ROWTYPE, the construct depends on object. If object is altered, the constructs that depend on object are invalidated.
Dependencies among PL/SQL library units (packages, stored procedures, and stored functions) can be handled either with timestamps or with signatures.
Oracle dynamically recompiles an invalid view or PL/SQL program unit the next time it is used. Alternatively, you can force the compilation of an invalid view or program unit using the appropriate SQL command with the COMPILE parameter.
Forced compilations are most often used to test for errors when it is known that a dependent view or program unit is invalid, but is not currently being used; therefore, automatic recompilation would not otherwise occur until the view or program unit is executed.
Invalid dependent objects can be identified by querying the data dictionary views USER_OBJECTS, ALL_OBJECTS, and DBA_OBJECTS - see "Listing Dependency Management Information" on page 15-6 for examples.
To recompile a view, use the ALTER VIEW command with the COMPILE parameter. The following statement recompiles the view EMP_DEPT contained in your schema:
ALTER VIEW emp_dept COMPILE;
To manually recompile a view, the view must be contained in your schema or you must have the ALTER ANY TABLE system privilege.
To recompile a procedure or function (stand-alone), use the ALTER PROCEDURE or ALTER FUNCTION command with the COMPILE clause. For example, the following statement recompiles the stored procedure UPDATE_SALARY contained in your schema:
ALTER PROCEDURE update_salary COMPILE;
To recompile either a package body or both a package specification and body, use the ALTER PACKAGE command with the COMPILE parameter. For example, the following SQL*Plus statements recompile just the body and the body and specification of the package ACCT_MGMT_PACKAGE, respectively:
SQLPLUS> ALTER PACKAGE acct_mgmt_package COMPILE BODY; SQLPLUS> ALTER PACKAGE acct_mgmt_package COMPILE PACKAGE;
All packages, procedures, and functions can be recompiled using the following syntax. The objects are compiled in dependency order, enabling each to be compiled only once.
SQLPLUS> EXECUTE DBMS_UTILITY.COMPILE_ALL;
You can manually recompile a procedure or package only if it is contained in your schema and you have the ALTER ANY PROCEDURE system privilege.
An existing trigger, enabled or disabled, can be manually recompiled using the ALTER TRIGGER command. For example, to force the compilation of the trigger named REORDER, enter the following statement:
ALTER TRIGGER reorder COMPILE;
To recompile a trigger, you must own the trigger or have the ALTER ANY TRIGGER system privilege.
The following data dictionary views list information about direct dependencies and dependency management:
Consider the following statements for Examples 1 and 2:
CREATE TABLE emp . . .; CREATE PROCEDURE hire_emp BEGIN . . . END; ALTER TABLE emp . . . ;
The ALL_OBJECTS data dictionary view lists information about all the objects available to the current user and the current status (that is, valid or invalid) of each object. For example, the following query lists the names, types, and current status of all objects available to the current user:
SELECT object_name, object_type, status FROM all_objects;
The following results might be returned:
OBJECT_NAME OBJECT_TYPE STATUS --------------- --------------- ------------ EMP TABLE VALID HIRE_EMP PROCEDURE INVALID
The DBA_DEPENDENCIES data dictionary view lists all dependent objects in the database and the objects on which they directly depend. For example, the following query lists all the dependent objects in JWARD's schema:
SELECT name, type, referenced_name, referenced_type FROM sys.dba_dependencies WHERE owner = 'JWARD';
If JWARD issued the example statements at the beginning of this section, the following results might be returned:
NAME TYPE REFERENCED_NAME REFERENCED_TYPE ----------- ------------ ------------------- --------------- HIRE_EMP PROCEDURE EMP TABLE
The *_DEPENDENCIES data dictionary views provide information about only the direct dependencies of objects. As a supplement, you can use a special dependency tracking utility to list both direct and indirect dependents of an object.
To create the dependency tracking utility, you must run the SQL script UTLDTREE.SQL. The location of this file is operating system dependent. The UTLDTREE.SQL script creates the following schema objects:
A temporary table used to store dependency information returned by the DEPTREE_FILL procedure.
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A view that lists dependency information in the DEPTREE_TEMPTAB table. The parent object is listed with a NESTED_LEVEL of 0, and dependent objects are listed with a nested level greater than 0.
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A view that lists dependency information in the DEPTREE_TEMPTAB table. Output is in a graphical format, with dependent objects indented from the objects on which they depend.
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A sequence used to uniquely identify sets of dependency information stored in the DEPTREE_TEMPTAB.
A procedure that first clears the DEPTREE_TEMPTAB table in the executor's schema, then fills the same table to indicate the objects that directly or indirectly depend on (that is, reference) the specified object. All objects that recursively reference the specified object are listed, assuming the user has permission to know of their existence.
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If you run the UTLDTREE.SQL script and use the utility while connected as INTERNAL, dependency information is gathered and displayed not only for dependent objects, but also for dependent cursors (shared SQL areas).
These SQL statements show how the UTLDTREE utility can be used to track dependencies of an object. Assume the following SQL statements:
CONNECT scott/tiger; CREATE TABLE scott.emp ( .... ); CREATE SEQUENCE scott.emp_sequence; CREATE VIEW scott.sales_employees AS SELECT * FROM scott.emp WHERE deptno = 10; CREATE PROCEDURE scott.hire_salesperson (name VARCHAR2, job VARCHAR2, mgr NUMBER, hiredate DATE, sal NUMBER, comm NUMBER) IS BEGIN INSERT INTO scott.sales_employees VALUES (scott.emp_sequence.NEXTVAL, name, job, mgr, hiredate, sal, comm, 10; END; CREATE PROCEDURE scott.fire_salesperson (emp_id NUMBER) IS BEGIN DELETE FROM scott.sales_employees WHERE empno = emp_id; END; SELECT * FROM scott.emp; SELECT * FROM scott.sales_employees; EXECUTE scott.hire_salesperson ('ARNALL', 'MANAGER', 7839, / SYSDATE, 1000, 500); EXECUTE scott.fire_salesperson (7934);
Assume that before SCOTT alters the EMP table, he would like to know all the dependent objects that will be invalidated as a result of altering the EMP table. The following procedure execution fills the DEPTREE_TEMPTAB table with dependency information regarding the EMP table (executed using Enterprise Manager):
EXECUTE deptree_fill('TABLE', 'SCOTT', 'EMP');
The following two queries show the previously collected dependency information for the EMP table:
SELECT * FROM deptree; NESTED_LEV TYPE OWNER NAME SEQ# ---------- ---------- -------------- ------------------ ---- 0 TABLE SCOTT EMP 0 1 VIEW SCOTT SALES_EMPLOYEES 1 2 PROCEDURE SCOTT FIRE_SALESPERSON 2 2 PROCEDURE SCOTT HIRE_SALESPERSON 3 SELECT * FROM ideptree; DEPENDENCIES ---------------------------------------- TABLE SCOTT.EMP VIEW SCOTT.SALES_EMPLOYEES PROCEDURE SCOTT.FIRE_SALESPERSON PROCEDURE SCOTT.HIRE_SALESPERSON
Alternatively, you can reveal all of the cursors that depend on the EMP table (dependent shared SQL areas currently in the shared pool) using the UTLDTREE utility. After connecting as INTERNAL and collecting dependency information for the table SCOTT.EMP, issue the following two queries:
SELECT * FROM deptree; NESTED_LEV TYPE OWNER NAME SEQ# ---------- ------ -------- ---------------------------- ---- 0 TABLE SCOTT EMP 0 1 CURSOR <shared> "select * from scott.emp 0.5 2 CURSOR <shared> "select * from scott.sa. . . 7.5 3 CURSOR <shared> "BEGIN hire_salesperson. . . 9.5 3 CURSOR <shared> "BEGIN fire_salesperson. . . 8.5 SELECT * FROM ideptree; DEPENDENCIES ------------------------------------------------------------ TABLE STEVE.EMP CURSOR <shared>."select * from scott.emp" CURSOR <shared>."select * from scott.sales_employee" CURSOR <shared>."BEGIN hire_salesperson ('ARN. . . CURSOR <shared>."BEGIN fire_salesperson (7934) END"
