Performance Tuning of web pages

By Ritesh M Nayak

• Offers a good user experience

• No broken functionality

• Part of SLAs for many projects

• Doesn’t make one feel like they are living in the 90s

Why is speed important?

Does anyone remember this?

Why is speed important?

Speed is the new SEO

remember the 80/20 rule

10 to 20% of the end user response time is spent downloading the actual HTML content of

the page, the rest is used to download the components of a page.

Audit of a popular webpage

Load time: 26 seconds

Page size: 5.2 MB

Requests: 172 HTTP requests

This is horribly wrong

Follow these basic rules if you want to improve performance

Please download the Yslow plugin for firefox or use the Chrome’s built in Audit feature

1. Make fewer HTTP requests

• Combine JS and CSS files

• Use sprites instead of individual images

• Inline images

Let’s talk a little bit about HTTP 1.1 and browser implementations here

2. Use a CDN

• Understand what server proximity constraints are and choose accordingly

• CDNs are inexpensive these days and can make a great difference to your application

Ex: Rackspace’s CloudFiles, Amazon’s CloudFront or Akamai

at $10c /GB/Month it is totally worth it

3.Use the Expires header

• Helps restrict unnecessary requests

• Use expires date in the far future

• HTTP 1.1 also supports cache-control , so use the max-age with a high value

HTTP/1.1 200 OK Content-Type: application/x-javascript Last-Modified: Thu, 10 Mar 2011 12:23:32 GTM Expires: Thu, 10 Mar 2032 18:23:32 GTM

On Apache, look at the mod_expires module for more info

4. GZIP components

• Helpful in conserving bandwidth

• Compress all text responses

• Use the vary header if you use proxies

• Don’t use ETAGS in the header

GET /sample.com/index HTTP/1.1 HOST: sample.com Accept-Encoding: gzip,deflate

On Apache, look at the mod_zip and mod_deflate for more info 50%

5. CSS on top

• Users don’t get to see un-styled content/white screen

• Drop all inline styles if possible and don’t use browser specific CSS effects (esp. IE)(not cached)

• Progressive rendering

Avoid CSS expressions ! background-color: expression( (new Date()).getHours()%2 ? "#B8D4FF" : "#F08A00" );

6. JS at the bottom

• Helps in unblocking parallel downloads

• DOM is mostly accessible unless you are doing something fancy

• Order them in the way you want them executed

• Drop inline scripts (not cached)

7. Reduce DNS lookups

• Typically takes 20-120 ms to look up a domain

• As a practice, don’t use more than 4 hostnames

8. Minify Javascript

• Reduced bandwidth significantly

• Use asset mgmt. libraries like assetic(php), static resources (grails)

• It is also useful to Obfuscate JavaScript sometimes to protect your code against attacks

9. Avoid redirects

• Creates a lot of Idle time for the user

• Use only for POSTs, but not for tracking, rewrite

Look at mod_rewrite best practices when using the module

10. Cache AJAX requests

• Use GET requests for AJAX (uses 1 packet)

• Seem fairly obvious but not done by people

• Especially for auto-complete textboxes or commonly occurring states like checking for username availability etc

To override the caching, append current timestamp to the ajax

request as a query parameter ?thetimeis=42392991821

11. Caching caching caching

• Use memcached; can be deployed separately

• Use database level caching via ORMs or other similar libraries. Consistent queries also help optimize query tuning

• Cache commonly hit pages (interpreted languages)

12. flush()

• Use PHPs flush() function to render a partially complete HTML page, so that the components can start loading instead of the browser remaining idle

More info here: http://php.net/manual/en/function.flush.php

13. Pre/post loading components

• Post load components which are out of the immediate viewport of the user.

Example: scripts not needed at DOM load

• Pre load components rendered as part of a container refresh

14. Split components on domains

• To maximize parallel downloads, use different subdomains (stick to 4 hostnames)

• Use a cookieless subdomain/domain for components

15. Minimize , cut , snip , chop

• Minimize DOM elements. Slows down JS

• Minimize IFrame (block page onload)

• Minimize 3rd party scripts. See if you load those asynchronously

• Reduce the cookie size (more info here)

• Optimize images, use PNG instead of GIF. Reduce JPG quality. Tools like jpgtran, pngcrush, optipng will help, remove exif and comments

Mobile Browser

• Keep components under 25kb

• Minify HTML in addition to js and css

• Use multipart documents (email)