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Querying Queues

Sometimes it may be necessary to inspect the content of a queue as a whole. You may want to know how many messages the queue contains, or you may want to ensure that the application has processed all of the messages for a service that you are about to take offline. You may need to find out why messages are not being processed by an application.

To get this information, use the name of the queue as the source table of a SELECT statement. A SELECT statement on a queue has the same format as a SELECT statement on a view or a table.

NoteNote

Service Broker is designed to allow multiple queue readers to efficiently receive messages from a queue. However, a SELECT statement on a queue may cause blocking. When using a SELECT statement on a queue, specify the NOLOCK hint to avoid blocking applications that use the queue.

For a description of the columns in a queue, see CREATE QUEUE (Transact-SQL).

Following is an example SELECT statement to find out the number of messages in the queue ExpenseQueue:

SELECT COUNT(*) FROM dbo.ExpenseQueue WITH (NOLOCK) ;

The following SELECT statement lets the administrator learn whether the queue ExpenseQueue contains any messages for the service //Adventure-Works.com/AccountsPayable/Expenses:

IF EXISTS(SELECT * FROM dbo.ExpenseQueue WITH (NOLOCK) WHERE
          service_name = '//Adventure-Works.com/AccountsPayable/Expenses')
  PRINT 'The queue contains messages for ' +
        '//Adventure-Works.com/AccountsPayable/Expenses'
ELSE
  PRINT 'The queue does not contain messages for ' +
        '//Adventure-Works.com/AccountsPayable/Expenses' ;

Service Broker manages updates to queues. Although the name of a queue can be used in place of a table name in a SELECT statement, a queue cannot be the target of an INSERT, UPDATE, DELETE, or TRUNCATE statement. SQL Server does not allow users to create indexes on queues.

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