** WORK IN PROGRESS **

This is just a placeholder for the full article that is in progress.

The problem

My BTS solution was receiving thousands of messages at once. After processing by BTS I needed to send them on via one of several WCF services depending on the message content. The problem is that due to the asynchronous nature of BizTalk the WCF services were getting hammered and could not cope with the load.

Note: It is possible to limit the SOAP calls in the BtsNtSvc.exe.Config file but that does not have the desired results for Net-TCP WCF services.

The solution

So I created a new MessageType for the messages in question and posted them to the BTS messaeg box. This schema included the URL they were being sent to as a promoted property. I then subscribed to the message type from a new orchestraton (that does just the WCF send) using the URL as a correlation ID. This created a singleton orchestraton that was instantiated when the first message hit the message box. It then waits for further messages with the same correlation ID and type and processs them one at a time using a loop shape with a timer (A pretty standard pattern for processing related messages)

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This limits the number of calls to the individual WCF services to 1. Which is a good start but the service can handle more than that and I didn't want to create a bottleneck. So I then constructed the Correlation ID using the URL concatinated with a random number between 1 and 10. This makes 10 possible correlation IDs per URL and so 10 instances of the singleton Orchestration per WCF service. Just what I needed and the upper random number is a configuration value in SSO so I can change the maximum connections without touching the code.