{"id":1267,"date":"2011-08-29T17:39:36","date_gmt":"2011-08-29T06:39:36","guid":{"rendered":"http:\/\/blog.mozilla.org\/nnethercote\/?p=1267"},"modified":"2011-08-29T17:50:48","modified_gmt":"2011-08-29T06:50:48","slug":"browser-x-is-using-y-mb-of-memory-with-z-tabs-open-is-a-meaningless-observation","status":"publish","type":"post","link":"https:\/\/blog.mozilla.org\/nnethercote\/2011\/08\/29\/browser-x-is-using-y-mb-of-memory-with-z-tabs-open-is-a-meaningless-observation\/","title":{"rendered":"“Browser X is using Y MB of memory with Z tabs open” is a meaningless observation"},"content":{"rendered":"

I read an exchange<\/a> today about the memory usage of Firefox 7 (which is currently in beta<\/a>).<\/p>\n

It uses 600 MB of RAM with 10 tabs open (different websites).<\/p>\n

lol wut? I’m not getting the same results as you. I have 12 tabs open here… RAM usage rarely exceeded 300mb for me. That’s already much better than Chrome, which seems to be using 190mb for just 2 tabs.<\/p>\n

Memory consumption is around 300 MB for me too.<\/p><\/blockquote>\n

I’ve seen variants of this exchange countless times.\u00a0 Unfortunately, observations such as “browser X is using Y MB of memory with Z tabs open” are meaningless<\/strong>.\u00a0 To understand why, consider this alternative, hypothetical exchange:<\/p>\n

I ran 3 different programs on my computer, they took 55 seconds to finish.<\/p>\n

lol wut?\u00a0 I just ran 8 programs and they only took 20 seconds to finish!<\/p><\/blockquote>\n

You’d never see an exchange like that, because it’s obvious that a comparison of the run-time of multiple programs is meaningless if you don’t specify what those programs are.\u00a0 Workload matters<\/strong>. And yet, people make comparisons of browser memory usage like this all the time.<\/p>\n

Here’s a simple example to show why this isn’t meaningful.\u00a0 I just did some memory measurements with a development build of Firefox 9, using a moderately-used profile with no add-ons installed.\u00a0 First I started it and opened 10 instances of www.google.com.au<\/a>, one per tab, and the resident set size<\/a> (RSS) was 139MB.\u00a0 Then I re-started it and opened 10 instances of gmail.com<\/a>, and the RSS climbed to 651MB.<\/p>\n

\"\"<\/a><\/p>\n

This is hardly surprising.\u00a0 gmail.com is a fully-fledged email client.\u00a0 www.google.com.au is not much more than a search box.<\/p>\n

Why do people so often make these meaningless “Y MB of memory with Z tabs open” comments?\u00a0 My theory is that it’s because most people have no idea how complicated web browsers and web pages are.\u00a0 Mild experience with HTML authoring is endemic — heaps of people have thrown together a basic web page, and it’s just a document with with some structure and styling, right?\u00a0 So they think the difference between the website they wrote for their scout troop in 1997 (the one with the “under construction” animated GIF) and the front page of TechCrunch<\/a> is merely a difference of degree, not kind.<\/p>\n

They’re wrong.\u00a0 For one, HTML and related technologies are hugely more powerful and complicated now than they were a few years ago.\u00a0 Also, their scout troop website probably didn’t contain multiple megabytes of JavaScript code tracking its visitors’ every move. A web browser is not a document viewer, it is a full-blown programming environment with some very sophisticated text and graphical capabilities.\u00a0 A web page is not a document but a program.\u00a0 Therefore, the memory (and CPU) usage of different web pages varies dramatically.<\/p>\n

Here’s a check-list of information that you should include if you want an observation about browser memory usage to be meaningful.<\/p>\n