On Sun, Apr 27, 2014 at 12:06 PM, Ori Livneh ori@wikimedia.org wrote:
Making 12 API calls means you run into browser connection limits[1].
We make 3 to 5 requests per image depending on circumstances (3 should be much more common). Image data loading is queued, so we fire of the first batch of requests for the current image, wait until all of those have been finished, fire the requests for the next image, wait again, fire the requests for the image preceding the current one. Thus the connection limits are not exceeded (on modern browsers anyway).
The overhead for each discrete request is substantial as well. I strongly suspect that combining the calls would substantially improve real-world user experience, but rather than relying on hunches I'd really like to see a controlled experiment that compares the two approaches. Would it be difficult to make MMV's code choose one or the other approach at runtime?
It should be fairly easy as long as we are talking about merging all the API requests for the same image. Merging all the requests for all images (i.e. loading all the data for 3 images in a single request) would be more complicated, but it is probably less useful for comparison anyway - as I said, the current code does not make all those requests in parallel.
While we are speaking about controlled experiments, would it be possible to perform some sort of load test with some sort of script generating API requests, instead of waiting until we find out server-side performance problems the hard way? Changing the pattern of requests in a text file is much easier than doing it in live JS code that actually relies on those requests; and while it would not answer questions about client-side performance effect, it would be probably more useful for estimating effects on server load than any live experiment we could be doing with MediaViewer in its current, relatively low-traffic state. We might want to do a similar test with image requests as well, to check the load on scalers, given that MediaViewer is requesting sizes that were typically not used before.