Brotli for static resources

Question

I recently enabled Brotli compression at one of the CDN platform that we use. With this I was expecting the performance to improve since the resources sizes gets reduced by 15-30% but to my surprise I see that the performance is still the same.

I did check various metrics and all looks still the same except ttfb where I see an increase of 10-15 miliseconds per resource.

Has anyone seen this before and if yes, what are the best ways to go about this issue? I am also suspecting that chrome might be taking longer time to decompress the resources when its brotli than Gzip but unfortunately I do not have any way to measure that time.

Answer 1

There is not enough detail to answer question. Performance is relative and so the gains due to Brotli may be getting drowned out by bigger performance issues with your site.

Some questions for you to answer for yourself:

• Is Brotli setup correctly and working? Can you see br as the content-encoding in developer tools network tab? Note you may need to add the content encoding column.
• Are you using HTTPS on your site (required by all browsers to use Brotli)? Did you move to HTTPS as part of this move? Is your HTTPS optimised.
• Has the overall size of your site gone down once you enabled Brotli? If so by how much? If you have lots of 10Mb print-quality images on your site and you have changed your HTML from being 50kb to 45kb then you may not see much of an overall difference.
• How long does your page take to generate? If your page takes 30 seconds to generate because the HTML is dynamic and your backend (app server, data server, whatever) is slow, then going to 29.5 seconds won’t seem that much.
• Do you have lots of render-blocking CSS and JavaScript. These are text so should hopefully be delivered faster now but if they are massively complex and processing time on the client is large then the download time may be an insignificant part of this.
• Are you testing from your company office while sitting 50metres from your data centre with a high speed 1000Mbps Ethernet connection which is basically talking straight into the web server? If so download speeds are going to be negligible no matter what the size of the downloads.

Brotli should compress text smaller. It can take longer/more processing power to do that compression than gzip but the network gains versus the CPU costs are usually worth it.

It is not magic however, and cannot make up for other performance issues on a site.