Oracle Event Based Job

I don't understand what those queue are in Oracle
and why event based job needs to use queue and agent?
anyone can explain it in a simple way?
Thank you!
mawinghoAsked:
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Wasim Akram ShaikConnect With a Mentor Commented:
Mawingho,

Why Events are needed in general is:

I will explain you a scenario,

Queues are used when there is an integration with external systems and the response from the other external system is asynchronous

 you will queue the data from your application and will send that data to other application/system by the interface and as we are unaware when the external system would respond we will place events.

Whenever the external system sends the response, the event gets generated and will dequeue the response and goes on for further processing.

This is the normal scenario where in the queues are used.
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Wasim Akram ShaikCommented:
Queues are basically data structures.

Oracle has implemented queues in relational database model.

As you are aware that Queue logic is FIFO(First IN First Out) model.

To implement this in Database, Oracle has come up with this approach, QUEUE a combination of QUEUE+QUEUE_TABLE

QUEUE TABLE has all the records which is actual data, queue has some external parameters to manage out the FIFO concept.

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mawinghoAuthor Commented:
that's make some sense to me now.
Ok, then why event based job need to enqueue before the database can raise an event?
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slightwv (䄆 Netminder) Commented:
I think the docs have all the information you need:
http://docs.oracle.com/cd/E11882_01/server.112/e25494/scheduse005.htm#CHDDDIJB

>>then why event based job need to enqueue before the database can raise an event?

If it was backwards the triggering event would have nothing in queue for the event.  You need to queue up the message then trigger the event.
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