Intersession Communication Oracle Database PL/SQL 10g Programming Chapter 11

Intersession Communication Intersession Communication Definition DBMS_PIPE Built-in Package DBMS_ALERT Built-in Package 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_PIPE Interactive intersession communication is: The process of sending messages from one open session in the database to another. The process works by accessing a messaging buffer, known as a pipe. Pipes are FIFO (First-in and last-out) queues. The pipes can be local, private, and public. The process uses the DBMS_PIPE built-in package to send and receive messages. 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_PIPE: Local Buffer 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_PIPE: Local Buffer Write DECLARE message VARCHAR2(30); success INTEGER; BEGIN message := DBMS_PIPE.UNIQUE_SESSION_NAME; DBMS_PIPE.RESET_BUFFER; DBMS_PIPE.PACK_MESSAGE(message); DBMS_OUTPUT.PUT_LINE('Message ['||message||'] '); END; / 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_PIPE: Local Buffer Read DECLARE message VARCHAR2(30); success INTEGER; BEGIN DBMS_PIPE.UNPACK_MESSAGE(message); DBMS_OUTPUT.PUT_LINE('Message ['||message||'] '); END; / 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_PIPE: SGA Named Pipe 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_PIPE: Create a Pipe DECLARE message_pipe VARCHAR2(30) := 'PLSQL$MESSAGE_INBOX'; success_size INTEGER := 2000; retval INTEGER; BEGIN retval := DBMS_PIPE.CREATE_PIPE(); IF (retval = 0) THEN DBMS_OUTPUT.PUT_LINE('Message ['||message||'] '); END IF; END; / '||message||' 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_PIPE: Write to a Pipe DECLARE flag INTEGER; BEGIN DBMS_PIPE.PURGE('PLSQL$MESSAGE_INBOX'); DBMS_PIPE.PACK_MESSAGE('MESSAGE'); DBMS_PIPE.SEND_MESSAGE('PLSQL$MESSAGE_INBOX'); END; / 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_PIPE: Read from a Pipe DECLARE message VARCHAR2(4000); flag INTEGER; BEGIN DBMS_PIPE.RESET_BUFFER; -- Force immediate read of pipe. flag := DBMS_PIPE.RECEIVE_MESSAGE('PLSQL$MESSAGE_INBOX',0); DBMS_PIPE.UNPACK_MESSAGE('MESSAGE'); DBMS_PIPE.SEND_MESSAGE('PLSQL$MESSAGE_INBOX'); END; / '||message||' 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_ALERT Event-driven intersession communication is: DBMS_ALERT built-in sends messages through a pipe: The transaction-based DBMS_ALERT lets a database trigger send an alert message to an implicit public pipe. DBMS_ALERT uses a publish-and-subscribe pattern where multiple sessions can register interest in an alert. Subscribers, those who register: Wait on the event for a polling interval. Read ONLY the last message received by the pipe because it is a single element queue. 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_ALERT: Publish on Event CREATE OR REPLACE TRIGGER signal_message AFTER INSERT OF message_id, message ON messages FOR EACH ROW BEGIN IF :old.message_id IS NULL THEN DBMS_ALERT.SIGNAL('EVENT_MESSAGE_QUEUE',:message); END IF; END; / '||message||' 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_ALERT: Subscribe BEGIN -- Subscribe to an alert event. DBMS_ALERT.REGISTER('EVENT_MESSAGE_QUEUE'); END; / 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Intersession Communication DBMS_ALERT: Catch DECLARE message VARCHAR2(4000); flag INTEGER; BEGIN DBMS_ALERT.WAITONE('EVENT_MESSAGE_QUEUE' ,message,status,30); END; / '||message||' 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)

Oracle Database PL/SQL 10g Programming (Chapter 11) Summary Database Trigger Concepts DDL Triggers DML Triggers Instead-of Triggers System or Database Event Triggers 2006 Oracle Database PL/SQL 10g Programming (Chapter 11)