Wilfried Mausz

Oracle Advanced Queueing

Wilfried Mausz

Agenda

• Queues• Models• Requirements• Creating and using a queue• Live demos

– Point-to-point queue in PL/SQL– Publish-Subscribe– Accessing a queue from .net

Wilfried Mausz

Queues

• Definition queue– Priority queue

• Definition enqueue and dequeue• Feature list• Scenarios for the use of queues• Examples

Wilfried Mausz

Queue

• A Queue can be visualized as a queue of people.

• People join the tail of the queue and wait until they reach the head.

Queue

Wilfried Mausz

Queue

• Definition:

http://en.wikipedia.org/wiki/Queue, 2004-12-03

In providing services to people, and in computer science, transportation, and operations research a queue is a First-In-First-Out FIFO process — the first element in the queue will be the first one out.

This is equivalent to the requirement that whenever an element is added, all elements that were added before have to be removed before the new element can be removed.

Wilfried Mausz

Priority queue

• A priority queue is an abstract data type supporting the following two operations:

– add an element to the queue with an associated priority – remove the element from the queue that has the highest priority,

and return it

http://en.wikipedia.org/wiki/Priority_queue, 2004-12-03

Wilfried Mausz

Enqueue and dequeue

• Enqueue … writing message to queue

• Dequeue … reading (and removing) message from queue

queuepayload

queue payload

Wilfried Mausz

Features

• Asynchronous communication between database applications

• Integration of messaging and database• Internet support (HTTP, Email, …)• Message queueing is transactional• Transformation of messages• Priority queues• Scheduled queues• Interfaces to other systems (IBM MQSeries, Tibco, …)

http://www.oracle.com/technology/products/aq/htdocs/aq9i_overview.html

Wilfried Mausz

Features

http://www.oracle.com/technology/products/aq/htdocs/aq9i_overview.html, 2004-12-04

Overview Advanced Queues

Wilfried Mausz

Scenarios

• Asynchronous import and export of data• Asynchronous working on data• Communication between different applications• Scheduled operations on data• E-business applications

– Communication with trading partners

• Enterprise Application Integration (EAI)

• Example: Milestone Export Application

Wilfried Mausz

Models

• Point-to-point queue• Publish-Subscribe model

Wilfried Mausz

Point-to-Point model

• Two systems using one ore more queues to communicate with each other

• One message just can be dequeued once

Application Application

Queues

enqueue dequeue

Wilfried Mausz

Publish-Subscribe model

• No connection between the applications• More than one receiving applications (agents)• Publisher applications put messages to the queue

(topics)• Messages are addressed for specific applications or

received by all– Broadcast (like TV, radio)– Multicast (like newspaper)

Application

Application

ApplicationApplication

Queues

publish

publish/ subscribe/ receive

subscribe/ receive

Wilfried Mausz

Requirements

• Oracle database (>8)• Packages• Permissions

Wilfried Mausz

Packages

• DBMS_AQADM – Creating or dropping queue tables that contain one or more

queues – Creating, dropping, and altering queues, which are stored in a

queue table– Starting and stopping queues in accepting message creation or

consumption

• DBMS_AQ – Creating a message to the specified queue – Consuming a message from the specified queue

http://www.unix.org.ua/orelly/oracle/bipack/ch05_01.htm, 2004-12-02

Wilfried Mausz

Permissions

• AQ administrator– Create queues– Owner of queues

• Queue users– Access queues

Wilfried Mausz

Permissions

CREATE ROLE my_aq_adm_role;GRANT CONNECT, RESOURCE, aq_administrator_role

TO my_aq_adm_role;

CREATE ROLE my_aq_user_role;GRANT CREATE SESSION, aq_user_role

TO my_aq_user_role;

Wilfried Mausz

Permissions

EXEC DBMS_AQADM.GRANT_SYSTEM_PRIVILEGE( privilege => 'ENQUEUE_ANY', grantee => 'my_aq_user_role', admin_option => FALSE);

EXEC DBMS_AQADM.GRANT_SYSTEM_PRIVILEGE( privilege => 'DEQUEUE_ANY', grantee => 'my_aq_user_role', admin_option => FALSE);

Wilfried Mausz

Permission

CREATE USER aqadm IDENTIFIED BY aqadm DEFAULT TABLESPACE tab TEMPORARY TABLESPACE temp;GRANT my_aq_adm_role TO aqadm;

CREATE USER aquser IDENTIFIED BY aquser DEFAULT TABLESPACE tab TEMPORARY TABLESPACE temp;GRANT my_aq_user_role TO aquser;

Wilfried Mausz

Creating a queue

• Payload• Queue table• Queue

Wilfried Mausz

Payload

• New datatype (object)• Execute permissions on that type

CREATE TYPE queue_message_type AS OBJECT(no NUMBER,title VARCHAR2(30),text VARCHAR2(2000) );

GRANT EXECUTE ON queue_message_typeTO my_aq_user_role;

Wilfried Mausz

Create queue

• Create queue table

EXEC DBMS_AQADM.CREATE_QUEUE_TABLE( queue_table => 'queue_message_table', queue_payload_type => aqadm.queue_message_type');

Wilfried Mausz

Create queue

• Create queue on queue table• Start queue

EXEC DBMS_AQADM.CREATE_QUEUE( queue_name => 'message_queue', queue_table => 'queue_message_table');

EXEC DBMS_AQADM.START_QUEUE( queue_name => 'message_queue');

Wilfried Mausz

Using the queue

• Create message• Enqueue• Dequeue

Wilfried Mausz

Using the queue

• Connect as queue user• Create message (payload type)• Enqueue message• Dequeue message

queuepayload payload

enqu

eue

dequ

eue

Wilfried Mausz

Using the queue (write)

DECLARE queue_options DBMS_AQ.ENQUEUE_OPTIONS_T; message_properties DBMS_AQ.MESSAGE_PROPERTIES_T; message_id RAW(16); my_message aqadm.queue_message_type;BEGIN my_message := aqadm.queue_message_type(

1,'This is a sample message','This message has been posted on ' ||TO_CHAR(SYSDATE,'DD.MM.YYYY HH24:MI:SS'));

DBMS_AQ.ENQUEUE(queue_name => 'aqadm.message_queue',enqueue_options => queue_options,message_properties => message_properties,payload => my_message,msgid => message_id);

COMMIT;END;

Wilfried Mausz

Using the queue (read)

SET SERVEROUTPUT ON;DECLARE    queue_options DBMS_AQ.DEQUEUE_OPTIONS_T;    message_properties DBMS_AQ.MESSAGE_PROPERTIES_T;    message_id RAW(2000);    my_message aqadm.queue_message_type;BEGIN    DBMS_AQ.DEQUEUE(        queue_name => 'aqadm.message_queue',        dequeue_options => queue_options,        message_properties => message_properties,        payload => my_message,        msgid => message_id );    COMMIT;    DBMS_OUTPUT.PUT_LINE('Dequeued no: ' || my_message.no);    DBMS_OUTPUT.PUT_LINE('Dequeued title: ' || my_message.title);    DBMS_OUTPUT.PUT_LINE('Dequeued text: ' || my_message.text);END;

Wilfried Mausz

Timing message

• Change delay of the message property• Delay in seconds

BEGIN my_message := aqadm.queue_message_type(

1,'This is a sample message','This message has been posted on ' ||TO_CHAR(SYSDATE,'DD.MM.YYYY HH24:MI:SS'));

message_properties.delay := 60; DBMS_AQ.ENQUEUE(

queue_name => 'aqadm.message_queue',enqueue_options => queue_options,message_properties => message_properties,payload => my_message,msgid => message_id);

queue

payload

payload

?

Wilfried Mausz

Conclusion

• Powerful mechanism to transport messages inside the database, as well to external programs

• Reduces database lookups for data export• Asynchronous processing of data (fire and forget)• Timing and priority possible• Availible in PL/SQL useable in every programming

environment

Wilfried Mausz

Literature

• http://www.unix.org.ua/orelly/oracle/bipack/ch05_01.htm, 2004-12-03

• http://www.akadia.com/services/ora_advanced_queueing.html, 2004-12-02

• http://en.wikipedia.org/wiki/Queue, 2004-12-03

Wilfried Mausz

Table of images

• Queue, http://www.cs.jhu.edu/~pari/600.107/Horstmann/slides/Ch19/ch19.html, 2004-11-30

• Overview Advanced Queueshttp://www.oracle.com/technology/products/aq/htdocs/aq9i_overview.html, 2004-12-04