Optimizing Page Load Times

John Callender writes, "Google engineer Aaron Hopkins has written an interesting analysis of optimizing page load time. Hopkins simulated connections to a web page consisting of many small objects (HTML file, images, external javascript and CSS files, etc.), and looked at how things like browser settings and request size affect perceived performance. Among his findings: For web pages consisting of many small objects, performance often bottlenecks on upload speed, rather than download speed. Also, by spreading static content across four different hostnames, site operators can achieve dramatic improvements in perceived performance."

Comments

HTTP/1.1 Design

[keithmo]

From TFA:

By default, IE allows only two outstanding connections per hostname when talking to HTTP/1.1 servers or eight-ish outstanding connections total. Firefox has similar limits.

And:

If your users regularly load a dozen or more uncached or uncachable objects per page load, consider evenly spreading those objects over four hostnames. Due to browser oddness, this usually means your users can have 4x as many outstanding connections to you.

From RFC 2616, section 8.1.4:

Clients that use persistent connections SHOULD limit the number of simultaneous connections that they maintain to a given server. A single-user client SHOULD NOT maintain more than 2 connections with any server or proxy.

It's not a browser quirk, it's specified behavior.