Flex client/server performance

I had a chance recently to do some Flex-based client/server development work with a small team. During the course of this project questions arose about data transfer using various protocols. Originally the team decided to use a SOAP interface, and this started out fine, but during development someone accidentally requested a deeply-nested graph of objects - and we hit a wall where data retrieval started taking many seconds.

Time for some performance testing, comparing three different protocols:
- SOAP marshaled into ActionScript class-based objects
- RESTful/JSON marshaled into dynamic objects (using as3corlib for JSON decoding)
- RESTful/XML marshaled into the ObjectProxy objects that Flex 3 creates by default

Basic results - the above list shows the performance ranking, SOAP being 3X to 7X slower than the RESTful/XML case.
JSON decoding added approx 20% overhead - presumably because it all happens in AS3 code rather than in native code.

The other thing that stood out - increasing the object graph depth caused an exponential increase in processing time, even though there was only a linear increase in the number of objects in the graph.

Another advantage of the RESTful/XML case is that the ObjectProxy objects created are directly bindable by the Flex UI controls, so if you can live with 'duck-typing' no further marshaling is required.

Later, on a different test setup, the speed of AMF3 was tested, and it was a little faster, with the added advantage (to some) that it was marshaling into class-based objects. (It also handles object graphs better because it uses server-side instance folding). But its a binary format with a limited user base.

Conclusions for now - another strike against SOAP in this environment, RESTful/XML ends up being a pretty compromise in performance and usefulness in the UI.