Oracle DBMS_PIPE is a part of the Oracle Database supplied packages that allows different sessions to communicate within the same Oracle instance through a pipe mechanism. This mechanism enables message passing using a producer-consumer model, making it especially useful for inter-process communication within the database environment.

The DBMS_PIPE.UNPACK_MESSAGE procedure is a critical component of this communication framework. It is used to read or unpack data from a message that has been received in a pipe. When a session sends a message using DBMS_PIPE.PACK_MESSAGE and then transfers the message through DBMS_PIPE.SEND_MESSAGE, the receiving session uses DBMS_PIPE.UNPACK_MESSAGE to extract the contents of the message.


    data    OUT 

Where is the type of the data being unpacked. This could be a number, date, character data, or even raw data. The procedure supports various data types to accommodate different kinds of information that might be communicated between sessions.


The UNPACK_MESSAGE procedure is used after a message has been received with DBMS_PIPE.RECEIVE_MESSAGE. The receiving process typically involves:

Calling RECEIVE_MESSAGE to check for and retrieve a message from a pipe.
Using UNPACK_MESSAGE one or more times to extract each piece of data from the message in the order it was packed.
It’s important to match the data type and order of UNPACK_MESSAGE calls with the PACK_MESSAGE calls used to create the message. If the types or order do not match, errors may occur, leading to exceptions or incorrect data retrieval.


Consider two sessions where one is sending a message containing an employee’s ID (a number) and name (a string):

Sender session

    DBMS_PIPE.PACK_MESSAGE(1001); -- Employee ID
    DBMS_PIPE.PACK_MESSAGE('John Doe'); -- Employee Name

Receiver session

    v_emp_id NUMBER;
    v_emp_name VARCHAR2(100);
    IF DBMS_PIPE.RECEIVE_MESSAGE('employee_info') = 0 THEN
        -- Process the received information
        DBMS_OUTPUT.PUT_LINE('Employee ID: ' || v_emp_id);
        DBMS_OUTPUT.PUT_LINE('Employee Name: ' || v_emp_name);
    END IF;

In this example, the receiver checks for a message in the ’employee_info’ pipe. If a message is found (indicated by RECEIVE_MESSAGE returning 0), it unpacks the message to retrieve the employee ID and name in the order they were packed and then processes the information.


Ensure that the order and data types of UNPACK_MESSAGE calls match those of the DBMS_PIPE.PACK_MESSAGE calls.
The pipe used for communication (in this case, ’employee_info’) must be the same in both sender and receiver sessions.
Effective use of DBMS_PIPE requires careful handling of message structures, especially in complex data exchange scenarios.