Link prefetching is used to identify a resource that might be required by the next navigation, and that the user agent SHOULD fetch, such that the user agent can deliver a faster response once the resource is requested in the future.
<link rel="prefetch" href="http://www.example.com/images/sprite.png" />
<link rel="prefetch" href="/images/sprite.png" />
- MSIE 11+/Edge
- Firefox 3.5+ (for HTTPS)
I’ve always been fan of tools for automation of development and testing. I’ve used SonarQube for a long time, and even connect it to my IDE (usually Eclipse), so that I can act on any warnings for code as I’m working on it.
SonarLint takes that to a new level, as it gives notifications before the code is even commited for SonarQube to analyze.
While the instructions here are for Eclipse, SonarLint is also available for IntelliJ IDEA, VisualStudio, and as a command line tool for download from the website.
Eclipse Update Site:
In addition to dns-prefetch, you can take browser performance one step further by actually creating a new connection to a resource.
By initiating an early connection, which includes the DNS lookup, TCP handshake, and optional TLS negotiation, you allow the user agent to mask the high latency costs of establishing a connection.
- Firefox 39+ (Firefox 41 for crossorigin)
- Chrome 46+
<link rel="preconnect" href="//example.com" />
<link rel="preconnect" href="//cdn.example.com" crossorigin />
I often get into some fringe areas of micro-optimizations of website performance, DNS prefetching is another one of those topics.
To understand how this can help, you must first understand the underlying concepts that are used within the communications used to build your web page.
The first of these is a “DNS Lookup”, where the domain name (www.example.com) is converted into a numerical address, the IP address of the server that contains the file(s).
In many websites, content is included from other domains for performance or security purposes.
When the domain names are known in advance, this approach can save time on the connection as the lookup can fetched in advance, before it is required on the page to retrieve assets.
This can be particularly useful for users with slow connections, such as those on mobile browsers.
<link rel="dns-prefetch" href="//www.example.com" />
- MSIE9+ (MSIE10+ as dns-prefetch)/Edge
If you’ve recently upgraded your network from IPv4 to IPv6, you might find that some software no longer works as it had before. Apache Tomcat is one that I recently stumbled upon, as it seems to prefer the IPv6 connection and stops listening on IPv4 with the default configuration.
The solution is simple, you just have to tell the server to listen on all incoming IP addresses. This worked for me with versions 7.x and 8.x, and I suspect that older and newer versions would be similar.
sudo vi /opt/tomcat/conf/server.xml
- To each
<Server> entry add:
- Restart Tomcat
As an IT professional, I’ve long been aware of the impending IPv4 exhaustion. To the layperson, this can easily be compared to phone numbers… there are now so many devices connected to the Internet that the size of the number used to identify and reach each of them uniquely is impossible.
IPv6 is a newer addressing system that supports a drastically increased number of addresses/numbers for use. Unfortunately, like Digital TV (in the US), adoption and migration of users and websites is slow.
To do your part as a user, you can change the settings in your gateway/router/modem to allow for IPv6 DNS lookups as most providers already support IPv6 traffic.
You can test your connection here:
Here are a few common values, I’ve also provided the Comcast/Xfinity values for reference:
- 188.8.131.52 (resolver1.opendns.com)
- 184.108.40.206 (resolver2.opendns.com)
- 220.127.116.11 (resolver3.opendns.com)
- 18.104.22.168 (resolver4.opendns.com)