Analysing website download sizes


When I go to watch football matches at Tottenham, I find it interesting to see the scores and summaries of other teams during e.g. the half time break. There are many sites and applications that can do this. One I use often is the BBC website, where they have a page that summarises what is happening “around the grounds” in one page, with a list of “comments”. A comment might look as follows: –

90+2 mins Man City 1-0 Everton

Throw to Everton deep inside their own half. They have to hurry up.

Some comments may be longer. Others will have images or thumbnails alongside them. But the basic idea is to let you know what is happening across all the games in the Premier League (there are usually 4-5 games being played at once, but sometimes this can rise up to 10)

If my mobile phone network provider EE are not playing up, and I can get reception, then I will use that site at half time, full time, and sometimes mid-way through the game if there’s a stoppage for e.g. injury. The problem is that the site has recently had a bit of an overhaul and I’ve noticed that it sometimes takes age to load, so I wanted to find out why this was – was it EE or just the new BBC site design?

Analysing website performance

The site’s changed because in the past it used to simply be a static list of “comments” that would auto refresh on a regular interval; it’s now more like a SPA, with a static HTML shell with JS, plus a dynamically updating set of data in the centre. It also now loads in two parts – first, a subset of data that contains the 10 most recent comments, and then a button to load all comments for the day (for a typical Saturday, this might be up to 500 comments).

To capture the data, I used the excellent debugging and profiling support built into Firefox that lets you monitor network activity and then divide it up based on the type of data e.g. HTML or CSS. I then put that into a simple F# script and then used FSPlot to push it into HighCharts in a variety of graphs.

Some of the results were quite surprising.

The first is that in the “initial” load of the page (just to see the ten most recent comments), you have to download an astonishing 2.2MB of data, across 85 files. Worst still is how this is spread: –

chart1To put it another way – around two-thirds of the data is taken up by JavaScript or images, some more for the HTML shell and CSS, and a measly 3.5% is used for those actual ten most recent comments that you want to read. It gets even worse if you then click the “load all comments” button: –

chart2

That’s right. Over 9mb of data needs to be downloaded on your phone just to see what’s happening with the eight or ten teams playing football today. Whilst the JS, CSS and HTML shell are unchanged, over 7mb is taken up by 192 images (some of which weigh in at over 700k each). The extra content file (containing the remaining 400+ text comments) comes in at about 700k in total, which accounts for around 8% of the total amount download (although whilst this in itself is in JSON, there’s embedded HTML within the payloads).

Conclusion

BBC web team – this is not a good experience. Even on my desktop PC, when I click the “load all comments” button, it locks Firefox for a couple of seconds when it downloads the remaining comments and then associated images etc. And the main use case is very simple: –

As a football fan, I want to quickly read what is happening around the grounds so that I can laugh/cry at the results.

Nowhere in the above sentence does it say anything about wanting to wait 5 minutes whilst it loads a million images. Nowhere does it say anything about wanting to use up a percentage of my data plan for tons of irrelevant pictures. I just want to read some football commentary!

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