18 Schema Object Dependency

Session State and Referenced Packages

Each session that references a package construct has its own instantiation of that package, including a persistent state of any public and private variables, cursors, and constants. All of a session's package instantiations, including state, can be lost if any of the session's instantiated packages are subsequently invalidated and revalidated.

Security Authorization

When a data manipulation language (DML) object or system privilege is granted to, or revoked from, a user or PUBLIC, Oracle Database invalidates all the owner's dependent objects, to verify that an owner of a dependent object continues to have the necessary privileges for all referenced objects.

Add Items to End of Package

When adding items to a package, add them to the end of the package. This preserves the entry point numbers of existing top-level package items, preventing their invalidation.

For example, consider this package:

CREATE OR REPLACE PACKAGE pkg1 IS
  FUNCTION get_var RETURN VARCHAR2;
END;
/

Adding an item to the end of pkg1, as follows, does not invalidate dependents that reference the get_var function:

CREATE OR REPLACE PACKAGE pkg1 IS
  FUNCTION get_var RETURN VARCHAR2;
  PROCEDURE set_var (v VARCHAR2);
END;
/

Inserting an item between the get_var function and the set_var procedure, as follows, invalidates dependents that reference the set_var function:

CREATE OR REPLACE PACKAGE pkg1 IS
  FUNCTION get_var RETURN VARCHAR2;
  PROCEDURE assert_var (v VARCHAR2);
  PROCEDURE set_var (v VARCHAR2);
END;
/

Reference Each Table Through a View

Reference tables indirectly, using views, enabling you to:

• Add columns to the table without invalidating dependent views or dependent PL/SQL objects

• Modify or delete columns not referenced by the view without invalidating dependent objects

The statement CREATE OR REPLACE VIEW does not invalidate an existing view or its dependents if the new ROWTYPE matches the old ROWTYPE.

Dependencies Among Local and Remote Database Procedures

Dependencies among stored procedures (including functions, packages, and triggers) in a distributed database system are managed using either time-stamp checking or signature checking (see "Time-Stamp Dependency Mode" and "RPC-Signature Dependency Mode").

The dynamic initialization parameter REMOTE_DEPENDENCIES_MODE determines whether time stamps or signatures govern remote dependencies.

Dependencies Among Other Remote Objects

Oracle Database does not manage dependencies among remote schema objects other than local-procedure-to-remote-procedure dependencies.

For example, assume that a local view is created and defined by a query that references a remote table. Also assume that a local procedure includes a SQL statement that references the same remote table. Later, the definition of the table is altered.

Therefore, the local view and procedure are never invalidated, even if the view or procedure is used after the table is altered, and even if the view or procedure now returns errors when used. In this case, the view or procedure must be altered manually so that errors are not returned. In such cases, lack of dependency management is preferable to unnecessary recompilations of dependent objects.

Dependencies of Applications

Code in database applications can reference objects in the connected database. For example, Oracle Call Interface (OCI) and precompiler applications can submit anonymous PL/SQL blocks. Triggers in Oracle Forms applications can reference a schema object.

Such applications are dependent on the schema objects they reference. Dependency management techniques vary, depending on the development environment. Oracle Database does not automatically track application dependencies.

Time-Stamp Dependency Mode

Whenever a procedure is compiled, its time stamp is recorded in the data dictionary. The time stamp shows when the procedure was created, altered, or replaced.

A compiled procedure contains information about each remote procedure that it calls, including the schema, package name, procedure name, and time stamp of the remote procedure.

In time-stamp dependency mode, when a local stored procedure calls a remote procedure, Oracle Database compares the time stamp that the local procedure has for the remote procedure to the current time stamp of the remote procedure. If the two time stamps match, both the local and remote procedures run. Neither is recompiled.

If the two time stamps do not match, the local procedure is invalidated and an error is returned to the calling environment. All other local procedures that depend on the remote procedure with the new time stamp are also invalidated.

Time stamp comparison occurs when a statement in the body of the local procedure calls the remote procedure. Therefore, statements in the local procedure that precede the invalid call might run successfully. Statements after the invalid call do not run. The local procedure must be recompiled.

If DML statements precede the invalid call, they roll back only if they and the invalid call are in the same PL/SQL block. For example, the UPDATE statement rolls back in this code:

BEGIN

  UPDATE table SET ...
  invalid_proc;
  COMMIT;

END;

But the UPDATE statement does not roll back in this code:

UPDATE table SET ...
EXECUTE invalid_proc;
COMMIT;

The disadvantages of time-stamp dependency mode are:

• Dependent objects across the network are often recompiled unnecessarily, degrading performance.

• If the client-side application uses PL/SQL, this mode can cause situations that prevent the application from running on the client side.

  An example of such an application is Oracle Forms. During installation, you must recompile the client-side PL/SQL procedures that Oracle Forms uses at the client site. Also, if a client-side procedure depends on a server procedure, and if the server procedure changes or is automatically recompiled, you must recompile the client-side PL/SQL procedure. However, no PL/SQL compiler is available on the client. Therefore, the developer of the client application must distribute new versions of the application to all customers.

RPC-Signature Dependency Mode

Oracle Database provides RPC signatures to handle remote dependencies. RPC signatures do not affect local dependencies, because recompilation is always possible in the local environment.

An RPC signature is associated with each compiled stored program unit. It identifies the unit by these characteristics:

• Name

• Number of parameters

• Data type class of each parameter

• Mode of each parameter

• Data type class of return value (for a function)

An RPC signature changes only when at least one of the preceding characteristics changes.

A compiled program unit contains the RPC signature of each remote procedure that it calls (and the schema, package name, procedure name, and time stamp of the remote procedure).

In RPC-signature dependency mode, when a local program unit calls a subprogram in a remote program unit, the database ignores time-stamp mismatches and compares the RPC signature that the local unit has for the remote subprogram to the current RPC signature of the remote subprogram. If the RPC signatures match, the call succeeds; otherwise, the database returns an error to the local unit, and the local unit is invalidated.

For example, suppose that this procedure, get_emp_name, is stored on a server in Boston (BOSTON_SERVER):

CREATE OR REPLACE PROCEDURE get_emp_name (
  emp_number  IN  NUMBER,
  hiredate    OUT VARCHAR2,
  emp_name    OUT VARCHAR2) AS
BEGIN
  SELECT last_name, TO_CHAR(hire_date, 'DD-MON-YY')
  INTO emp_name, hiredate
  FROM employees
  WHERE employee_id = emp_number;
END;
/

When get_emp_name is compiled on BOSTON_SERVER, Oracle Database records both its RPC signature and its time stamp.

Suppose that this PL/SQL procedure, print_name, which calls get_emp_name, is on a server in California:

CREATE OR REPLACE PROCEDURE print_ename (emp_number IN NUMBER) AS
  hiredate  VARCHAR2(12);
  ename     VARCHAR2(10);
BEGIN
  get_emp_name@BOSTON_SERVER(emp_number, hiredate, ename);
  dbms_output.put_line(ename);
  dbms_output.put_line(hiredate);
END;
/

When print_name is compiled on the California server, the database connects to the Boston server, sends the RPC signature of get_emp_name to the California server, and records the RPC signature of get_emp_name in the compiled state of print_ename.

At run time, when print_name calls get_emp_name, the database sends the RPC signature of get_emp_name that was recorded in the compiled state of print_ename to the Boston server. If the recorded RPC signature matches the current RPC signature of get_emp_name on the Boston server, the call succeeds; otherwise, the database returns an error to print_name, which is invalidated.

Topics:

• Changing Names and Default Values of Parameters

• Changing Specification of Parameter Mode IN

• Changing Subprogram Body

• Changing Data Type Classes of Parameters

• Changing Package Types

PROCEDURE P1 (Param1 IN NUMBER := 100);
PROCEDURE P1 (Param2 IN NUMBER := 200);

PROCEDURE P1 (Param1 NUMBER);    -- implicit specification
PROCEDURE P1 (Param1 IN NUMBER);  -- explicit specification

CREATE OR REPLACE PROCEDURE get_hire_date (
  emp_number  IN  NUMBER,
  hiredate    OUT VARCHAR2,
  emp_name    OUT VARCHAR2) AS
BEGIN
  SELECT last_name, TO_CHAR(hire_date, 'DD-MON-YY')
  INTO emp_name, hiredate
  FROM employees
  WHERE employee_id = emp_number;
END;
/

CREATE OR REPLACE PROCEDURE get_hire_date (
  emp_number  IN  NUMBER,
  hiredate    OUT VARCHAR2,
  emp_name    OUT VARCHAR2) AS
BEGIN
  -- Change date format model
  SELECT last_name, TO_CHAR(hire_date, 'DD/MON/YYYY')
  INTO emp_name, hiredate
  FROM employees
  WHERE employee_id = emp_number;
END;
/

CHAR
CHARACTER

VARCHAR
VARCHAR2
STRING
LONG
ROWID

RAW
LONG RAW

BINARY_INTEGER
PLS_INTEGER
SIMPLE_INTEGER
BOOLEAN
NATURAL
NATURALN
POSITIVE
POSITIVEN

NUMBER
INT
INTEGER
SMALLINT
DEC
DECIMAL
REAL
FLOAT
NUMERIC
DOUBLE PRECISION

DATE
TIMESTAMP
TIMESTAMP WITH TIME ZONE
TIMESTAMP WITH LOCAL TIME ZONE
INTERVAL YEAR TO MONTH
INTERVAL DAY TO SECOND

CREATE OR REPLACE PROCEDURE get_hire_date (
  emp_number  IN  NUMBER,
  hiredate    OUT DATE,
  emp_name    OUT VARCHAR2) AS
BEGIN
  SELECT last_name, TO_CHAR(hire_date, 'DD/MON/YYYY')
  INTO emp_name, hiredate
  FROM employees
  WHERE employee_id = emp_number;
END;
/

CREATE OR REPLACE PACKAGE emp_package AS
  TYPE emp_data_type IS RECORD (
    emp_number  NUMBER,
    hiredate    VARCHAR2(12),
    emp_name    VARCHAR2(10)
  );
  PROCEDURE get_emp_data (
    emp_data  IN OUT emp_data_type
  );
END;
/

CREATE OR REPLACE PACKAGE emp_package AS
  TYPE emp_data_type IS RECORD (
    emp_num   NUMBER,
    hire_dat  VARCHAR2(12),
    empname   VARCHAR2(10)
  );
  PROCEDURE get_emp_data (
    emp_data  IN OUT emp_data_type
  );
END;
/

CREATE OR REPLACE PACKAGE emp_package AS
  TYPE emp_data_record_type IS RECORD (
    emp_num   NUMBER,
    hire_dat  VARCHAR2(12),
    empname   VARCHAR2(10)
  );
  PROCEDURE get_emp_data (
    emp_data  IN OUT emp_data_record_type
  );
END;
/

Controlling Dependency Mode

The dynamic initialization parameter REMOTE_DEPENDENCIES_MODE controls the dependency mode. If the initialization parameter file contains this specification, then only time stamps are used to resolve dependencies (if this is not explicitly overridden dynamically):

REMOTE_DEPENDENCIES_MODE = TIMESTAMP

If the initialization parameter file contains this parameter specification, then RPC signatures are used to resolve dependencies (if this not explicitly overridden dynamically):

REMOTE_DEPENDENCIES_MODE = SIGNATURE

You can alter the mode dynamically by using the DDL statements. For example, this example alters the dependency mode for the current session:

ALTER SESSION SET REMOTE_DEPENDENCIES_MODE = {SIGNATURE | TIMESTAMP}

This example alters the dependency mode systemwide after startup:

ALTER SYSTEM SET REMOTE_DEPENDENCIES_MODE = {SIGNATURE | TIMESTAMP}

If the REMOTE_DEPENDENCIES_MODE parameter is not specified, either in the init.ora parameter file or using the ALTER SESSION or ALTER SYSTEM statements, TIMESTAMP is the default value. Therefore, unless you explicitly use the REMOTE_DEPENDENCIES_MODE parameter, or the appropriate DDL statement, your server is operating using the time-stamp dependency mode.

When you use REMOTE_DEPENDENCIES_MODE=SIGNATURE:

• If you change the initial value of a parameter of a remote procedure, then the local procedure calling the remote procedure is not invalidated. If the call to the remote procedure does not supply the parameter, then the initial value is used. In this case, because invalidation and recompilation does not automatically occur, the old initial value is used. To see the new initial values, recompile the calling procedure manually.

• If you add an overloaded procedure in a package (a procedure with the same name as an existing one), then local procedures that call the remote procedure are not invalidated. If it turns out that this overloading results in a rebinding of existing calls from the local procedure under the time-stamp mode, then this rebinding does not happen under the RPC signature mode, because the local procedure does not get invalidated. You must recompile the local procedure manually to achieve the rebinding.

• If the types of parameters of an existing package procedure are changed so that the new types have the same shape as the old ones, then the local calling procedure is not invalidated or recompiled automatically. You must recompile the calling procedure manually to get the semantics of the new type.

Topics:

• Dependency Resolution

• Suggestions for Managing Dependencies