September 2013 Site Performance Report
As we enter the fourth quarter of 2013, it’s time for another site performance report about how we did in Q3. Our last report highlighted the big performance boost we saw from upgrading to PHP 5.4, and this report will examine a general front-end slowdown that we saw over the last few months.
Server Side Performance
Here are the median and 95th percentile load times for signed in users on our core pages on Wednesday, September 18th:
On the server side we saw a modest decrease on most pages, with some pages (e.g. the profile page) seeing a slight increase in load time. As we have mentioned in past reports, we are not overly worried about the performance of our core pages, so the main thing we are looking for here is to avoid a regression. We managed to achieve this goal, and bought ourselves a little extra time on a few pages through some minor code changes. This section isn’t very exciting, but in this case no news is good news.
Synthetic Front-end Performance
The news here is a mixed bag. As usual, we are using our private instance of WebPagetest to get synthetic measurements of front-end load time. We use a DSL connection and test with IE8, IE9, Firefox, and Chrome. Here is the data, and all of the numbers are medians over a 24 hour period:
The massive increase in document complete time on the listing page is due to the rollout of a page redesign, which is much heavier and includes a large number of web fonts. We are currently setting up a test to measure the impact of web fonts on customer engagement, and looking for ways to reduce page weight on the listing page. While document complete isn’t a perfect metric, 8 seconds is extremely high, so this bears looking into. That said, we A/B tested engagement on the old page and the new, and all of the business metrics we monitor are dramatically better with the new version of the listing page. This puts further doubt on the impact of document complete on customer behavior, and illustrates that performance is not the only thing influencing engagement – design and usability obviously play a big role.
Real User Front-end Performance
The effect here mirrors what we saw on the synthetic side – a general upward trend, with a larger spike on the listing page. These numbers are for the “page load” event in mPulse, which is effectively the onload event. As Steve Souders and others have pointed out, onload is not a great metric, so we are looking for better numbers to measure on the real user side of things. Unfortunately there isn’t a clear replacement at this point, so we are stuck with onload for now.
You can follow Jonathan on Twitter at @jonathanklein