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Understanding Collation and Service Broker

Service Broker is designed to let services and applications in instances with different collation configurations communicate easily and efficiently. The database that hosts a service that sends a message might not use the same collation as the database that hosts the service that receives the message. Therefore, Service Broker uses a consistent collation for names, regardless of the collation of the database that hosts the service. To remove collation information from the communication process, Service Broker uses a byte-by-byte comparison to match service names, contract names, and message type names. By matching names as sequences of bytes, Service Broker makes it simple for services to exchange messages correctly without the extra overhead of exchanging collation information.

The byte-by-byte match is effectively a binary comparison that does not consider the current collation. For this reason, many broker services find it convenient to follow the recommendations in Naming Service Broker Objects. An application that follows these guidelines and treats all names as case-sensitive should function correctly regardless of differences in collation between the database that hosts the target service and the database that hosts the initiating service.

Queues use a consistent collation regardless of the default collation of the SQL Server instance or the default collation of the database that hosts the queue. If a queue is the target of a SELECT statement that includes a JOIN statement with another table in the database, such as a table used to maintain state, you may be required to explicitly specify the collation for the comparison.

For example, an application that uses message retention may need to preserve some messages for a conversation before the application ends the conversation. The following Transact-SQL code sample saves all messages, for a given conversation, that have a message type name in the table AuditedMessageTypes.

IF @messageTypeName =
  'http://schemas.microsoft.com/SQL/ServiceBroker/EndDialog'
BEGIN
  INSERT INTO dbo.AuditRecord
    SELECT q.message_type_name, q.message_body
      FROM dbo.ApplicationQueue AS q
        JOIN dbo.AuditedMessageTypes AS am ON
             am.message_type_name = q.message_type_name
             COLLATE Latin1_General_BIN
           AND
             q.conversation_handle = @conversationHandle
   END CONVERSATION @conversationHandle
END

The SELECT statement explicitly specifies a binary comparison for matching the message type names. Because a queue does not use the database default collation, the COLLATE clause is required for the comparison am.message_type_name = q.message_type_name to succeed. The statement specifies a binary collation, Latin1_General_BIN, to match the behavior of the internal comparison that Service Broker uses to match service names.

Service Broker transmits the message body as binary data and does not modify the content of the message. If applications exchange data that is collation-sensitive, the applications must handle any collation differences. Applications that exchange text generally use Unicode types to help minimize collation problems.

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