APMdigest asked industry experts – from analysts and consultants to the top vendors – to outline the most important factors that impact website response time. The second installment of the list, featuring factors 6–10, covers the front end.

Start with Part 1 of "20 Top Factors That Impact Website Response Time"

6. WEB PAGE SIZE

In my experience, the single most consistent factor that contributes to slower load times is page size. All other things being equal, a fatter page is a slower page. In one study I conducted of 60 popular sites that used responsive design, only 20% rendered acceptably quickly — and these were also the only sites that were less than 1 MB in size. According to the HTTP Archive, the average web page today is more than 2 MB in size. This is something site owners should be aware of, and concerned about.
Tammy Everts
Senior Researcher & Evangelist, SOASTA

7. RESPONSIVE WEB DESIGN

Mobilegeddon already is upon us where Google gives higher priority for websites that are mobile friendly. Hence, the new race is to build websites that use responsive web design techniques. This could create performance problems if resources, such as images, are not properly managed. For example, including all variations of images (for tablet, desktop, mobile, retina display) in a CSS and including this CSS incorrectly in the webpage can end up loading all variations of the image in the background for every request, hence slowing down overall page load time.
Gibu Mathew
Director of Product Management, Site24x7

8. JAVASCRIPT

Radware has been studying the various factors that impact website response time for years. Aside from a steady increase in the volume of data required for each page, one of the largest impacts that we are seeing comes from the increasing dependency on JavaScript. When these scripts block execution or download slowly the overall site performance is directly impacted.
Kent Alstad
VP of Acceleration, Radware

14 Best Practices to Cure Your Website’s Performance Pains

9. WEB CONTENT AND CODE

As more and more code resides on the browser side as opposed to server side, one of the top factors impacting website response time is un-optimized browser side content like download of large images, no caching, too many redirects or DNS lookups. Using APM tools, you can see a very granular breakdown of end user response time from the browser and determine the bottleneck at a glance. You can see exactly how much time was spent on resolving DNS lookups, how much time was spent in downloading content, time spent in load event scripts and so forth. It is essential that developers fine tune their browser side code following best practices, cross test across browser types, devices and platforms, and keep an eye on the end user experience with predictive alerts to prevent slow downs.
Payal Chakravarty
Sr. Product Manager - APM, IBM

The top factor that affects website response time is full page load time. Nothing harms the user experience more than slow loading times, especially when multimedia, Flash, or other graphics are involved. Users will leave your site if the video they want to view won't load. Slow load times can be caused by content-heavy pages and poor code on the website side, or inadequate bandwidth on the user side. To ensure website performance, IT can use ping requests and loading time measurements (specifically, the time it takes to download source code) to track page speed. It is often simple to fix problems that cause slow load times, but it is critical to effectively measure what load times are across each browser and on mobile devices to understand when your website is performing poorly.
Amanda Karkula
Channel Sales Manager, Paessler AG

10. N+1 QUERIES

N+1 queries are a common web application anti-pattern that can cause slow website response time. It happens when a single application query runs other queries “automatically” - resulting in multiple queries running at once. For example, a user may be browsing through a photo gallery and while switching from one picture to another, comments get rendered along with the photos. To diagnose, N+1 issues, look into the log data - if you see one query for photos and one for "comments" generated for every photo returned by the original query, you've got an N+1 query on your hands.
Trevor Parsons
Chief Scientist, Logentries

Read Part 3 of "20 Top Factors That Impact Website Response Time"