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

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

3. 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.
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Oracle Database PL/SQL 10g Programming (Chapter 11)

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

5. 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; /
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Oracle Database PL/SQL 10g Programming (Chapter 11)

6. 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; /
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Oracle Database PL/SQL 10g Programming (Chapter 11)

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

8. 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||'
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Oracle Database PL/SQL 10g Programming (Chapter 11)

9. 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; /
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Oracle Database PL/SQL 10g Programming (Chapter 11)

10. 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||'
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Oracle Database PL/SQL 10g Programming (Chapter 11)

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.
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Oracle Database PL/SQL 10g Programming (Chapter 11)

12. 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||'
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Oracle Database PL/SQL 10g Programming (Chapter 11)

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

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

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