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Wednesday, December 12, 2012

A correlation between load time and usage

We frequently see reports of website usage going up as load time goes down, or vice-versa. It seems logical. Users use a site much more if it's fast, and less if it's slow. However, consider the converse too. Is it possible that a site merely appears to be faster because users are using it more, and therefore have more of it cached? I've seen sites where the server-side cache-hit ratio is much higher when usage is high resulting in lower latency. At this point I haven't seen any data that can convince me one way or the other. Do you?


Jared Barnett
December 12, 2012 2:24 PM

It seems to me like there could be two different types of sites that would have different explanations for this observation. I can imagine one type of site where you really would need lots of users hitting the site in order to cache much of the site. This site would have a lot of different content depending on user interaction or content that changes frequently. In those conditions, high traffic would be necessary to cache much of the site. Then, you might draw the conclusion that the high traffic is reducing load times because more of the site is cached.

But what about a different site that doesn't require a lot of users to cache most of its content. Maybe its content is relatively static or maybe most of its content, by nature, can't be cached (e.g. financial data during market hours). If you were seeing high traffic and low load times, then I think your first idea could apply: users are using the site because its fast.

What do you think? Does that make sense?

December 12, 2012 2:47 PM

Hi Jared, thanks for your comment.

Yes, I do think both types of sites exist, and there's a whole spectrum in between. For example, in the financial data site you mention, there could still be many static assets (JavaScript, CSS, Images, etc.) that are cached by the user's browser. In that case even a few users hitting the site many times will make it appear fast.

What we need is a set of metrics that help us determine what kind of site we have an which of the two is the cause and which is the effect.

It's hard to determine human behaviour when you can neither see nor speak to the humans in question.

December 12, 2012 4:34 PM

Yes that is definitely possible. More users using the site from various locations will warm up not only their own browser cache but also caches on various CDN instances replicating the site's static resources. Thus, the experience will be better. The site will appear faster even without any specific code changes.

Jared Barnett
December 12, 2012 5:35 PM

Another point to make is that when a site is loading quickly, you have the ABILITY to make more requests because you aren't waiting around as much.

December 13, 2012 5:18 AM

what about high usage lead to high latency(high load time) ? like irctc.co.in but still people use it to book the tickets.

December 13, 2012 10:07 AM

@namma yes, we see many sites like that. Performance is irrelevant for them because it's the only place to get a particular service. In a sense, it's a monopoly and can do/charge anything it wants without fear of losing customers.

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