Remote Dependencies

Signatures

To alleviate some of the problems with the timestamp-only dependency model, Oracle Database provides the additional capability of remote dependencies using signatures. The signature capability affects only remote dependencies. Local (same server) dependencies are not affected, as recompilation is always possible in this environment.

A signature is associated with each compiled stored program unit. It identifies the unit using the following criteria:

The user has control over whether signatures or timestamps govern remote dependencies.

See Also: "Controlling Remote Dependencies" on page 7-28

When the signature dependency model is used, a dependency on a remote program unit causes an invalidation of the dependent unit if the dependent unit contains a call to a subprogram in the parent unit, and if the signature of this subprogram has been changed in an incompatible manner.

Note: You may need to set up data structures, similar to the following, for certain examples to work:

CONNECT system/manager

CREATE PUBLIC DATABASE LINK boston_server USING 'inst1_alias'; CONNECT scott/tiger

CREATE OR REPLACE PROCEDURE get_emp_name (

Using Procedures and Packages 7-23

Remote Dependencies

BEGIN

SELECT ename, to_char(hiredate, 'DD-MON-YY')

INTO emp_name, hire_date

FROM emp

WHERE empno = emp_number;

END;

When get_emp_name is compiled on BOSTON_SERVER, its signature, as well as its timestamp, is recorded.

Suppose that on another server in California, some PL/SQL code calls get_emp_ name identifying it using a DBlink called BOSTON_SERVER, as follows:

CREATE OR REPLACE PROCEDURE print_ename (emp_number IN NUMBER) AS hire_date VARCHAR2(12);

ename VARCHAR2(10); BEGIN

get_emp_name@BOSTON_SERVER(emp_number, hire_date, ename); dbms_output.put_line(ename); dbms_output.put_line(hire_date);

END;

When this California server code is compiled, the following actions take place:

At runtime, during the remote procedure call from the California server to the Boston server, the recorded signature of get_emp_name that was saved in the compiled state of print_ename gets sent to the Boston server, regardless of whether or not there were any changes.

If the timestamp dependency mode is in effect, then a mismatch in timestamps causes an error status to be returned to the calling procedure.

However, if the signature mode is in effect, then any mismatch in timestamps is ignored, and the recorded signature of get_emp_name in the compiled state of Print_ename on the California server is compared with the current signature of get_emp_name on the Boston server. If they match, then the call succeeds. If they do not match, then an error status is returned to the print_name procedure.

Note that the get_emp_name procedure on the Boston server could have been changed. Or, its timestamp could be different from that recorded in the print_ name procedure on the California server, possibly due to the installation of a new

7-24 Oracle Database Application Developer's Guide - Fundamentals