Oracle Advanced Queues - missing messages and best approach to debug - oracle

Question

Env: Oracle 12c
I currently have an Oracle Advanced Queue system setup as follows:
NAME QUEUE_TABLE QID QUEUE_TYPE MAX_RETRIES RETRY_DELAY RETENTION
--------------- --------------- ------- --------------- ----------- ----------- ---------
MY_WORK_Q MY_WORK_QT 2518333 NORMAL_QUEUE 100 0 0
MY_WORK_QT_E MY_WORK_QT 2518332 EXCEPTION_QUEUE 0 0 0
I also have registered a callback that calls a PL/SQL package procedure.
For some reason, I seem to have a situation where I am losing messages or messages are not being dequeued.
Based on this, I have the following questions:
Have I setup my actual queue - MY_WORK_Q with MAX_RETRIES and other info correctly?
Is there a way to check messages that have been enqueued?
Is there a way to check messages that have been de-queued?
Is there a means of checking the EXCEPTION_QUEUE/Exception table to see if lost messages have reached there?
I just can't see why I am losing messages within my queueing system and what I could check to see what might be causing the issue.
I also increased my MAX_RETRIES to 100 but still seem to be having issues.
Update
It seems like I am getting the error ORA-25263: no message in queue.
I am not sure if this is related to a timing issue on the dbms_aq.enqueue or dbms_aq.dequeue calls but on the dbms_aq.dequeue I have this set:
l_dequeue_options.wait := dbms_aq.no_wait;
Do I require say a 10 second wait instead of no_wait? I am unsure if this possible and whether the wait needs to be on the enqueue or dequeue steps.

Answer 1

Here is a simple example that works. Perhaps you can use it to identify your issue?
-- DROP TYPE some_type_t FORCE;
CREATE OR REPLACE TYPE some_type_t AS OBJECT (
a NUMBER,
b VARCHAR(100),
c DATE
);
CREATE OR REPLACE PROCEDURE some_type_callback(CONTEXT IN RAW,
reginfo IN sys.aq$_reg_info,
descr IN sys.aq$_descriptor,
payload IN RAW,
payloadl IN NUMBER) AS
-- Local variables
v_dequeue_options dbms_aq.dequeue_options_t;
v_message_properties dbms_aq.message_properties_t;
v_message_handle RAW(26);
v_some_type some_type_t;
BEGIN
-- Set the dequeue options from the descriptor
v_dequeue_options.consumer_name := descr.consumer_name;
v_dequeue_options.msgid := descr.msg_id;
-- Dequeue the message
dbms_aq.dequeue(queue_name => descr.queue_name,
dequeue_options => v_dequeue_options,
message_properties => v_message_properties,
payload => v_some_type,
msgid => v_message_handle);
END some_type_callback;
/
SELECT *
FROM user_errors e
WHERE e.name = 'SOME_TYPE_CALLBACK';
BEGIN
-- dbms_aqadm.drop_queue_table(queue_table => 'some_type_qt',
-- force => TRUE);
dbms_aqadm.create_queue_table(queue_table => 'some_type_qt',
queue_payload_type => 'some_type_t',
multiple_consumers => TRUE);
dbms_aqadm.create_queue(queue_name => 'some_type_q',
queue_table => 'some_type_qt',
retention_time => 86400); -- 1 day
dbms_aqadm.start_queue(queue_name => 'some_type_q');
dbms_aqadm.add_subscriber(queue_name => 'some_type_q',
subscriber => sys.aq$_agent(NAME => 'some_type_qs',
address => NULL,
protocol => NULL));
dbms_aq.register(sys.aq$_reg_info_list(sys.aq$_reg_info('some_type_q:some_type_qs',
dbms_aq.namespace_aq,
'plsql://some_type_callback',
hextoraw('FF'))),
1);
END;
/
SELECT *
FROM aq$some_type_qt;
-- nothing
DECLARE
v_some_type some_type_t;
eopt dbms_aq.enqueue_options_t;
mprop dbms_aq.message_properties_t;
enq_msgid RAW(16);
BEGIN
v_some_type := some_type_t(a => 42,
b => 'forty-two',
c => to_date('1/1/2942',
'mm/dd/yyyy'));
dbms_aq.enqueue(queue_name => 'some_type_q',
enqueue_options => eopt,
message_properties => mprop,
payload => v_some_type,
msgid => enq_msgid);
END;
/
SELECT *
FROM aq$some_type_qt;
-- msg_state = READY => PROCESSED
One thing that will definitely help you is setting retention_time on your queue table. You can then use the aq$ reference for the queue table to look at the messages. The msg_state column will show READY for a fresh message and PROCESSED for a message that was consumed. There are some other columns on there that can be helpful: retry_count for example.
If you are getting ORA-25263 it seems instead of handling the one message you are getting provoked for in your callback that you are trying to read a different message and clashing with another job that was started to consume the queue. This is resolved by the two lines I have in my callback before calling dequeue.
If you need to trigger when a message arrives and then preserve message order you need to add some locking and additional complexity to your callback. You could take a look at Metalink 225810.1 for examples on how to do this.