[rap-dev] Scalability Details and Server-side Push

[Austin Riddle <austin.riddle@xxxxxxxx>]

Hello Stefan,

In response to your questions:

- How did you implement server-side push (you mentioned UICallbacks are not well suited where I fully agree).

We injected a polling loop into our custom clock widget that actually synchronized our client clock display with the server.  This took the form of some javascript in the custom widget that regularly initiates a request to the server. Since we could guarantee a request lifecycle at a certain interval, we could have the server post updates along with that client-initiated request.  In our dashboard application, it was imperative that it could just "sit" there and give status updates automatically. Nothing fancy:

_sendResponse : function(widget, field, value) {
	if (!org_eclipse_rap_rwt_EventUtil_suspend) {
		var wm = org.eclipse.swt.WidgetManager.getInstance();
		var canvasId = wm.findIdByWidget(widget);
		var req = org.eclipse.swt.Request.getInstance();
		req.addParameter(canvasId + "." + field, value);
		req.send();
	}
},
		
_onRefreshInterval : function(evt) {
	this._sendResponse(this, "refresh", true);
},
		
_startTimer : function() {
	var interval = this.getRefreshInterval();
	if (interval > 0) {
		if (this._timer == null) {
			this._timer = new qx.client.Timer(interval*1000);
			this._timer.addEventListener("interval", this._onRefreshInterval, this);
			this._timer.start();
		} else {
			this._timer.setInterval(interval);
		}
	}
	else if (this._timer != null) {
		this._timer.stop();
	}
}

- Did you really manage to run this app in IE6?
With pain and suffering... mainly from the slooooooow javascript engine, and we had some real issues with the client-side memory footprint. Sometimes the app would top out at 500 MB client-side.  We also had an extreme number of script timeout warnings on load. Some of the things we did to address these issues is to use lazy content providers and also to load our components through the span of multiple client requests.  That was a nice trick that worked well.

- What are your findings concerning performance, users per server, etc?
We have done some profiling on the server and our numbers indicate that we can support 500 users on a 32-bit Windows box.  We don't have any data thus far on the thread impact, but we are still investigating. So we are looking into virtualization options along with custom code to synchronize instances of the application.  We are somewhat constrained by the policies of the customer data centers.

I would be happy to answer any other questions.