The Oracle DBMS_PIPE package provides a mechanism for inter-process communication (IPC) between sessions within the same Oracle database. This feature enables different sessions to communicate with each other by sending and receiving messages through a virtual pipe, which is a memory-based structure. The DBMS_PIPE.CREATE_PIPE function within the DBMS_PIPE package is specifically used to create such a pipe.
Syntax
The basic syntax for the DBMS_PIPE.CREATE_PIPE function is as follows:
DBMS_PIPE.CREATE_PIPE(
pipe_name IN VARCHAR2,
max_message_size IN NUMBER DEFAULT 512,
private IN BOOLEAN DEFAULT FALSE
) RETURN NUMBER;
pipe_name: The name of the pipe to be created. It is a VARCHAR2 type and identifies the pipe uniquely within the database.
max_message_size: An optional parameter specifying the maximum size (in bytes) of a message that can be written to the pipe. The default size is 512 bytes.
private: An optional BOOLEAN parameter indicating whether the pipe is private (TRUE) or public (FALSE). A private pipe is accessible only by the session that created it, while a public pipe can be accessed by any session within the database. The default is FALSE, making the pipe public.
Return Value
The function returns a numeric code indicating the outcome of the operation:
0: Success. The pipe was created successfully.
1: A pipe with the specified name already exists.
Others: Other values indicate an error occurred during the creation of the pipe.
Usage
The DBMS_PIPE.CREATE_PIPE function is often used in scenarios where different sessions need to exchange data or signals without direct interaction or when asynchronous communication is required. For example, a background session might process data and use a pipe to send processing results or status updates to a front-end session.
Example
DECLARE
result NUMBER;
BEGIN
result := DBMS_PIPE.CREATE_PIPE('my_pipe');
IF result = 0 THEN
DBMS_OUTPUT.PUT_LINE('Pipe created successfully.');
ELSE
DBMS_OUTPUT.PUT_LINE('Error creating pipe. Code: ' || TO_CHAR(result));
END IF;
END;
This PL/SQL block attempts to create a pipe named ‘my_pipe’. It checks the return value of the CREATE_PIPE function and outputs a message indicating whether the pipe was created successfully.
Considerations
Security and Access Control: When using public pipes, be aware that any session can access the data sent through the pipe. Consider using private pipes for sensitive data or implementing additional access control mechanisms.
Resource Management: Pipes are memory structures. Excessive use of pipes or large messages may impact the database’s memory usage. It’s essential to manage pipes properly, including deleting them when they are no longer needed using the DBMS_PIPE.REMOVE_PIPE function.
Oracle’s DBMS_PIPE package, and specifically the CREATE_PIPE function, offers a powerful way to implement IPC within the Oracle database, facilitating complex workflows and communication patterns between sessions.