Reason why JSON output is going to be much faster in ArcGIS Server 9.4
At this year’s ESRI dev summit, ESRI was showing off how the performance of the JSON output generation by the ArcGIS Server REST API is going to be much faster. I was curious as to how this could be since it is the same JSON that is being generated. The answer turned out to be pretty simple. Here is how JSON is generated today
As you can see from the image above, at 9.3 the ArcGIS Server REST API does the work of reading (deserialize) the JSON sent in from the client (browser) over HTTP and converts (serialize) that appropriately into a SOAP message. This SOAP message is then sent over DCOM to the ArcGIS Server 9.3. The ArcGIS Server then converts the SOAP messages to ArcObjects types and does the work it needs to do. When the work is done, the ArcObjects types are converted back to SOAP and sent back to the REST API. The REST API then converts the SOAP types back to JSON and then sends the JSON results back to the client(browser).
In the 9.4, the JSON is going to be generated at the ArcGIS Server itself and thus avoiding a lot of serialization & deserialization to and from SOAP / JSON. Avoiding these intermediary data conversion steps are the primary reason for the increased performance of JSON output in 9.4.