#domainsharding

[hightechdad]

Been doing some #optimization on my site. Seems to be working! • • • • #wprocket #domainsharding #minification #prefetch #maxcdn #cloudflare #imagecompression

[rohannog]

On Domain sharding

The good

A few years ago around the time of IE 6, most browsers allowed only 2 parallel requests to a single domain. This was a problem for sites that stored multiple JS, CSS and image files on a single domain (See [1]). Along came domain sharding to the rescue. Now, you could use multiple domains while still storing everything in the same place.

The bad

However, using multiple domains means a new connection has to be made to each of these domains, which increases latency. Also, all modern browsers support 6 connections per domain. So, you shouldn't be using too many shards. From [2] and [3], 2 seems to be an optimum number.

Additionally, too many shards tends to increase network congestion in the browser as described in [4]

The ugly

Recent developments have further increased the costs of these new connections. They are:

Mobile traffic: Making an extra connection from a cellphone is very expensive and adds significantly to the latency of the page [5]

SPDY: SPDY works best when several components are loaded over a single connection. Sharding negates the advantages of SPDY [6]

SSL: SSL connections are very expensive due to the handshake and Certificate verification.

In summary, domain sharding is still useful, but it cannot be used as a big hammer. 2 domains seems to be ideal, but do test with your page and if possible, a bucket of real-world users.

Links:

[1] Sharding Dominant Domains by Steve Souders [2] Reducing Domain Sharding by Jonathan Klein [3] Domain Sharding revisited by Steve Souders [4] Network Congestion and Web Browsing by William Chan [5] Why Domain Sharding is Bad News for Mobile Performance and Users by Peter McLachlan [6] SPDY best practices by Chromium dev team