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Do asynchronous answers happen in DSS Rest API?
Client advised that in the past they were facing such asynchronous answers, which have been eliminated by using a special rule. Due to this they are no longer able to determine, if asynchronous answers still happen or not. The code they used to fix it cannot be repeated, thus the question if they need to develop a new rule? Or whether the asynchronous answers are not an issue anymore.
In a nutshell: yes, and this is a desirable feature.
In detail: the DSS REST API asynchronous mechanism is designed to support long running requests, which pose several problems:
The DSS REST API conforms to OASIS OData standards for async. In addition to the standard asynchronous protocol defined by OData, which supports polling and status and progress updates, we added the ability to cancel a request, as well as manage the list of active asynchronous jobs.
To avoid data retrieval issues, the recommend practice is to use the asynchronous mechanisms. Using synchronous mechanisms might result in issues, especially when requesting large data sets. The typical symptom will be data requests that timeout without returning any data; this can occur randomly, as the server load influences extraction times.
To me, the asynchronous behavior you described looks similar to a known issue patched in version 10.8, released early January 2017. The issue is that DSS incorrectly used async when there was no Prefer: respond-async option set.
You can find detailed information in this question and "Why do I get a 202 when I submit a synchronous request?" topic of the FAQ in the document page.
