I have built an orchestration with a loop to retreive paged data from REST web service. From page size and offset I am able to call the service for "next page" of data. Then I debatch it, map it to internal format and process it further. When one page is processed, I request next page from the REST web service.
As it turns out, the host running the orchestration and send ports causes the memory to constantly grow during processing of all the data, and eventually hit the throttling mode.
Why is memory not released when I am done with one page loop? Is it the "consumed" messages that are stored in the orchestration that builds up the memory? Is it possible to clear orchestration from these "consumed" messages, to release the memory used? (No message tracking active on the orchestration, or send ports.)
Apparently, there is no way to prohibit BizTalk Orchestrations from building up a list of messages in Orchestration, including used/processed/consumed messages. Putting things in Scope does not prohibit this behaviour.
Hence, for long-running Orchestrations there can be a lot of messages building up. Especially for singleton Orchestrations, where the general solution proposed to deal with this problem is to make sure Orchestration shuts down once in a while (when idle, e.g.).
My solution was to split the Orchestration into two, and have the initial Orchestration start the second Orchestration with the Start Orchestration, which in turn calls the second Orchestration recursively, and so on, until last page is received and the last Orchestration ends.