How to recieve and remove from queue

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Richard - 20 Apr 2006 00:41 GMT

Can someone explain the basics of how a message is put onto a queue, read
from that queue, and removed from that queue, when there is not a second SSB
instance? For example, a client requests information, an application queues
the request in the database, another application reads the request and
processes it, and then removes the queue.

The "from" and "to" service is a little confusing when there isn't a second
SSB.

Thanks,
Richard

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Kent Tegels - 20 Apr 2006 04:48 GMT

Hello Richard,

> Can someone explain the basics of how a message is put onto a queue,
> read from that queue, and removed from that queue, when there is not a
> second SSB instance? For example, a client requests information, an
> application queues the request in the database, another application
> reads the request and processes it, and then removes the queue.

1. Messages always go into a Queue with the SEND statement. The SEND statement
targets a Service which is responsible for reading the Message from the Queue.
Is some ways, a Service is a bit of indirection for a Queue.

2. When a message arrives, Service Broker inserts the Message into the Queue
and looks to see if needs to start any instances of a Service Program (typically
a stored procedure) that responsible for reading the Message from the Queue.
That process is known as activation.

3. The Service Program normally begins a transaction, asks the Queue for
the next available Conversation Group ID and then reads the next available
Message for that conversation group using the RECEIVE statement. If and when
that transaction commits, it removes the message from the Queue (the removal
is actually done by the receive, but that's covered by the transaction in
case of failure.)

In the case where you just have a single Queue and Service Program, you SEND
the Message TO the same Service that the Message is FROM. You need to say
that a Message is from a Service since that service receives error and other
system Messages from Service Broker that will probably need to be processed.

Helpful?

Thanks!
Kent Tegels
DevelopMentor
http://staff.develop.com/ktegels/

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