Asynchronous execution of reports and cubes

Starting in 2020 Update 2, the v2 Data APIs support asynchronous instance creation. This prevents the client from holding a thread or HTTP request open when report, cube, and dashboard execution takes longer than usual.

The parameter definitions are the same as previously designed. However, a new prefer header parameter has been added. This functionality follows the standards set forth in RFC 7240, that requests are processed in asynchronous mode if the value of the prefer header parameter contains "respond-async". Other features of prefer, such as wait, are not currently supported.

If prefer:respond-async is provided in an API request, such as /v2/reports/{id}/instances, the report instance is created based on input and then executed. The API call may return the results if they are available immediately or return an HTTP response of 202 (Accepted) along with a reference to the instance that can be used for polling.