abusing javascript to measure web performance
DESCRIPTION
While building boomerang, we developed many interesting methods to measure network performance characteristics using JavaScript running in the browser. While the W3C's NavigationTiming API provides access to many performance metrics, there's far more you can get at with some creative tweaking and analysis of how the browser reacts to certain requests.In this talk, I'll go into the details of how boomerang works to measure network throughput, latency, TCP connect time, DNS time and IPv6 connectivity. I'll also touch upon some of the other performance related browser APIs we use to gather useful information. I will NOT be covering the W3C Navigation Timing API since that's been covered by Alois Reitbauer in a previous Boston Web Perf talk.TRANSCRIPT
• Philip Tellis
• .com• [email protected]
• @bluesmoon• geek paranoid speedfreak• http://bluesmoon.info/
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I <3 JavaScript
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So much that I wore Mustache socks to my wedding
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I’m also a Web Speedfreak
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We measure real user website performance
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This talk is (mostly) about how we abuse JavaScript to do it
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Abusing JavaScript to Measure WebPerformance
Philip Tellis / [email protected]
Boston #WebPerf Meetup / 2012-07-24
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First, a note about the code
Note that in the code that follows,
+ new Date
is equivalent to
new Date().getTime()
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1Latency
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1 Blinking Lights
It takes about 16ms for light to get from SF to Boston(24ms through fibre)
. . .
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1 Blinking Lights
It takes about 16ms for light to get from SF to Boston(24ms through fibre)
Though it takes about 100ms to ping... why?
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1 HTTP
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So to measure latency, we need to send 1 packet each way, andtime it
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1 Network latency in JavaScript
var ts, rtt, img = new Image;img.onload=function() { rtt=(+new Date - ts) };ts = +new Date;img.src="/1x1.gif";
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1 Notes
• 1x1 gif is 35 bytes• including HTTP headers, is smaller than a TCP packet• Fires onload on all browsers• 0 byte image fires onerror• which is indistinguishable from network error
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2TCP handshake
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2 ACK-ACK-ACK
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2 Connection: keep-alive
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2 Network latency & TCP handshake in JavaScript
var t=[], tcp, rtt;var ld = function() {
t.push(+new Date);if(t.length > 2) // run 2 times
done();else {var img = new Image;img.onload = ld;img.src="/1x1.gif?" + Math.random()
+ ’=’ + new Date;}
};var done = function() {
rtt=t[2]-t[1];tcp=t[1]-t[0]-rtt;
};ld();
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Notice that we’ve ignored DNS lookup time here... how wouldyou measure it?
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3Network Throughput
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3 Measuring Network Throughput
data_lengthdownload_time
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Should you fly a 747 or a 737?
• A 747 seats 400+ passengers• A 737 seats about 150• Both take about the same time to fly from SFO to BOS• A 747 takes longer to load and unload
The best selling aircraft to date is the 737
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3 Network Throughput in JavaScript
// Assume global object// image={ url: ..., size: ... }var ts, rtt, bw, img = new Image;img.onload=function() {
rtt=(+new Date - ts);bw = image.size*1000/rtt; // rtt is in ms
};ts = +new Date;img.src=image.url;
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3 Measuring Network Throughput
If it were that simple, I wouldn’t be doing this talk.
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3 TCP Slow Start
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3 Measuring Network Throughput
So to make the best use of bandwidth, we need resources that fitin a TCP window
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3 There is no single size that will tax all available networks
http://www.yuiblog.com/blog/2010/04/08/analyzing-bandwidth-and-latency/
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3 Network Throughput in JavaScript – Take 2
// image object is now an array of multiple imagesvar i=0;var ld = function() {
if(i>0)image[i-1].end = +new Date;
if(i >= image.length)done();
else {var img = new Image;img.onload = ld;image[i].start = +new Date;img.src=image[i].url;
}i++;
};
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3 Measuring Network Throughput
Slow network connection, meet really huge image
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3 Network Throughput in JavaScript – Take 3
var img = new Image;img.onload = ld;image[i].start = +new Date;image[i].timer =
setTimeout(function() {image[i].expired=true
},image[i].timeout);
img.src=image[i].url;
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3 Network Throughput in JavaScript – Take 3
if(i>0) {image[i-1].end = +new Date;clearTimeout(image[i-1].timer);
}
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3 Network Throughput in JavaScript – Take 3
if(i >= image.length|| (i > 0 && image[i-1].expired)) {
done();}
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3 Measuring Network Throughput
Are we done yet?
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3 Measuring Network Throughput
Are we done yet?sure...
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3 Measuring Network Throughput
Except network throughput is different every time you test it
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Statistics to the Rescue
flickr/sophistechate/4264466015/
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3 Measuring Network Throughput
The code for that is NOT gonna fit on a slide
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But this is sort of what we see world-wide
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And it’s different for different countries
This is India
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4DNS
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4 Measuring DNS
time_with_dns − time_without_dns
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4 Measuring DNS in JavaScript
var t=[], dns, ip, hosts=[’http://hostname.com/’,’http://ip.ad.dr.ess/’];
var ld = function() {t.push(+new Date);if(t.length > hosts.length)done();
else {var img = new Image;img.onload = ld;img.src=hosts[t.length-1] + "/1x1.gif";
}};var done = function() {
ip=t[2]-t[1];dns=t[1]-t[0]-ip;
};ld();
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4 Measuring DNS
• What if the IP changes?• What if DNS is cached?• What if you map DNS based on geo location?
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4 Wildcard DNS Entries
*.foo.com→ IP address
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4 Measuring DNS in JavaScript – take 2
var base_url="http://*.foo.com/",timers = {}, gen_url="";
function start() {var random = Math.random().toString(36),
cache_bust = Math.random(),img = new Image();
gen_url = base_url.replace(/\*/, random);
img.onload = A_loaded;
timers.start = +new Date;img.src = gen_url + "image-l.gif?t=" + cache_bust;
}
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4 Measuring DNS in JavaScript – take 2
function A_loaded() {var cache_bust = Math.random(),
img = new Image();
img.onload = B_loaded;
timers.a_loaded = +new Date;img.src = gen_url + "image-l.gif?t=" + cache_bust;
}
I’ll let you figure out B_loaded
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4 Measuring DNS
Full code in boomerang’s DNS plugin
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5IPv6
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5 Measuring IPv6 support and latency
1 Try to load image from IPv6 host• If timeout or error, then no IPv6 support• If successful, then calculate latency and proceed
2 Try to load image from hostname that resolves only to IPv6host
• If timeout or error, then DNS server doesn’t support IPv6• If successful, calculate latency
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5 Measuring IPv6 support and latency
Full code in boomerang’s IPv6 pluginNote, only run this if you know IPv6 is supported by the client
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6Other Stuff
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6 Other Stuff We Measure
• NavTiming – navtiming.js
• navigation.connection.type – mobile.js
• window.performance.memory – memory.js
• Number of DOM nodes and byte size of HTML –memory.js
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And we try to do it fast
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–.done()
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Code/References
• http://lognormal.github.com/boomerang/doc/(BSD Licensed)
• www.lognormal.com
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• Philip Tellis
• .com• [email protected]
• @bluesmoon• geek paranoid speedfreak• http://bluesmoon.info/
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Thank youAsk me about a discount code
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