I've been doing some hunting to follow up on my previous posting regarding web service naming conventions and standards.  The pickings are slim.  Thomas Erl, a Canadian SOA expert and author, mentions some SOA naming conventions in an article he wrote for Oracle entitled Standardizing Service Endpoints. 

He prescribes a practical approach, naming services based on the utility (verb), entity (noun) or task/function (verb-noun -- do something to something), dependant on the scope and context of the service.  He also warns about ensuring that operations within the service reflect appropriately the scope of the service, and to eliminate redundancy in operation names.

From the article:

• The utility-centric context is found in application services involving operations that encapsulate cross-cutting functions, such as event logging, exception handling, or notification. These reusable services need to be labeled according to a specific processing context, agnostic in terms of any particular solution environment. For example, a utility service might be named Notify.
• An entity-centric context is established in a business service that represents a specific business entity, such as an invoice or a purchase order. The labeling of entity-centric business services is often predetermined by the entity name. For example, a service may simply be named Invoice or Customer.
• Task-centric contexts are required for services modeled to encapsulate process logic. In this case, the thread that ties together the grouped operations is a specific activity being automated by the service logic. Therefore, the use of verbs in service names is common. For example, a task-centric service may be called GetProfile or ProfileRetrieval, if that accurately represents the task's scope.

As with service names, labeling individual service operations is also a process that should be subject to standards and guidelines and for which there are already several best practices.

For example, the naming of the service itself ought to influence how the individual operations are labeled. Because a good service name will already clearly establish a meaning and a context, operation names should be streamlined to avoid the use of redundant wording. Take an operation that retrieves invoice history data for a service named Invoice. This operation does not need to be labeled GetInvoiceHistory, because the invoice context is already established by the service name. GetHistory would be sufficient.

Thomas really helped us move forward with our SOA initiative at CISTI both with a workshop to bootstrap our process, and through his books. 

Musings on Language and Design
Why it's better to be lazy
by Jeremy Meyer
June 8, 2008

Summary
Our parents were wrong when they told us not to be lazy. Laziness is a vital characteristic for success, and something we should strive for.

Classifying People

I have had recent to remember those 4 great classifications of people. Intelligent, Stupid, Active and Lazy.

My father often used to tell me about these classifications which he attributed to the Duke of Wellington. I have since read articles which have attributed them originally to Buddha, or some Buddhist swami, but the most credible source seems to suggest that they are more likely to have come from Helmuth Karl Gernhard Graf von Moltke, a German Military leader and strategist. (see below).

Actually it doesn't matter where they come from, the important thing is that they are an excellent insight into how and why people do things. If you haven't come across them before, they are very simple.

Everyone can be loosely classified into 4 groups, which are permutations of either activeness or laziness and , intelligence or stupidity.

Intelligent Lazy people, as my father would explain, are everyone's favourite. They do things in a smart way in order to expend the least effort. They don't rush into things, taking that little bit of extra time to think and find the shortest, best path. They tend to make what they do repeatable so they don't have to go through it all again. These people usually make good leaders, and they are good to have on teams.

Intelligent Active people are useful, because they are smart, after all, but their intelligence can be slightly diluted or tempered by their activity. Where they don't have a perfect solution, they might act anyway, rather than sitting on their laurels, so useful people but not great leaders, and on a team, they can often put noses out of joint by acting too early and too fast.

Stupid Lazy people have their place too, they are easy to manage, they generally don't act on their own initiative too much and, given tasks that are not beyond them, they will perform in a predictable, consistent manner. Usually they won't cause any harm on teams. Wellington, liked these people as foot soldiers.

Stupid Active people are the dangerous ones. Their default behaviour is to act, and in the absence of skill or thought they can cause all types of trouble.

Anecdotal Evidence

Stupid Active people are definitely good for one thing, though, they make for great anecdotes! They are the exclusive recipients of the Darwin awards, after all. We all know one of two of these, I bet if you think about it right now, you can think of at least one person you work with who you could classify immediately as stupid and active.

My own most recent amusing experience happened whilst on the management team for a large migration project. The team's task was to migrate UML Modelling projects from one version of UML to another, using Borland's Eclipse modelling tool, Together. In SCRUM tradition we had a daily call with our offshore team who were working on a backlog of many hundreds of projects that needed to be migrated. The task was fairly simple. Run the automated import facility, sanity check the project, and make any additional necessary changes to the UML model by hand.

One of the team, let's call him "Fred", reported that his progress was blocked by strange behaviour in his migrated Eclipse project. Diagrams were disappearing and reappearing and something was wrong. I noticed from his screen capture that something was awry with his project icons. I asked him to show me the contents of his Eclipse .project file. It contained the line..

<nature>uml14.uml14_nature</nature>

This is the line in the project file that tells Eclipse what type of project it is, and it told me that his automated import had failed. Clearly it had aborted, unable to convert the project from one type to another, no doubt due to corrupted input. I asked him to clean up the original UML diagrams, and re-try the import.

The following day, Fred reported that his icons were correct, but the project behaviour was still wrong. When I quizzed him on his approach, he explained that he had in fact edited the .project file by hand and changed the line above to:

<nature>uml20.uml20_nature</nature>

He had done this, he explained, because he had understood from what I had said that that particular line in the .project file was the problem. After much suppressed mirth, I patiently and politely explained that when changing the meta-model of one project to that of another, there was a great deal of work to be done, which is why it was automated, and why there was an import menu option for it. Manually changing the value of the "nature" tag in the project file didn’t change the nature of the project any more than wearing a baseball cap makes you a baseball player. To my astonishment, Fred defended himself with great verve. He stressed that he had "used his skills" in the best way he knew, to try and solve the problem. He seemed quite put out that I hadn't applauded his initiative. Not only was he actively stupid in his attempt to solve a problem, he was actively stupid in his attempt to justify it! Since he was my responsibility, but not my hire, I couldn't take what would have been my preferred action, firing him on the spot.

Everybody can be Stupid

Before I go on, I should say that Fred might well have been pretty smart in many ways. It has been my experience that you can't apply these classifications to people in general. There must be a context. You might be smart and lazy in your work, but stupid and active in the kitchen. I would like to believe that I am a smart, lazy software developer, but I am a very stupid, active DIY'er. Ask any of my friends who have been party to my crazy projects. My pond building exercise (where I cast my own bricks with moulds I made myself). Or my spontaneous tandoori oven, built from roof tiles at a holiday house in France (we ate cold, semi-raw chicken at 11pm that night). I am sure people do tend towards certain behaviours in all of their undertakings, but I think it is dangerous to apply the classifications generally. It is also hard to work with people whom you honestly believe are stupid in all walks of life. I have faith that there is something, somewhere that Fred does well and with careful consideration, but it certainly doesn't involve working with software tools.

Safety Net for Lemmings

My experience with Fred got me to thinking that when we create frameworks and even languages, we always try to cater for people like him. Some language designers feel this is their responsibility. Sometimes this is kind of helpful, like private methods and properties in a language, for example. Sometimes, it can be overly paternalistic. The old checked exception / unchecked exception debate springs to mind. C++ doesn't enforce the catching of an exception, Java does (with recent compromised made by Runtime exceptions). The question is, can you really defend yourself against active stupidity? Should you really try to defend yourself against it? Isn't it orthogonal to the actual intention of the effort, and just a bit like building safety nets on cliffs in case lemmings want to throw themselves off? (This is a metaphor, for more about the lemming myth, see the links below.) I was reviewing some code that looked like this, the other day:

   public void doStuff (int value) {
      try {
          applyCalculation();
      } catch (Exception e) {
      }
   }

Ah, that old chestnut. A swallowed, unlogged, unreported exception. It was lucky that I picked it up in the code review. This is a fine example of active stupidity in programming. It is actually less work, (less typing, even), and smarter to write:

	public void doStuff (int value) throws Exception {
		applyCalculation();
	}

.. clearly, having checked exceptions in your language is no defence against a developer who is this active.

Should we try and drop all of these types of controls in language and architectures? Of course not, it is just that there is unlikely to be a linguistic construct or design approach which can prevent active stupidity without being so infuriating as to be almost unusable by someone whose approach is more lazy and intelligent. The acknowledgement of that should lead to a happy medium between choking restrictions and complete lack of structure.

If you try to enforce exception handling, there will always be those who find a work-around for the construct. If you create a Singleton connection factory class to ensure a single point of connection there will always be someone who tries to hack their own independent connection to the server. If you try and enforce static type checking and make, say, a type-safe collection, there will always be someone who will explicitly typecast their Objects before they add them to make the code compile.. and so on.

It's People who Write Programs

Ultimately, until technology moves on significantly, it is people who are using programming languages and frameworks. The smart, lazy ones will be looking to reuse what they can and to find neat, idiomatic ways of achieving functionality. The active stupid people will be looking to "use their skills" like Fred did. And get stuff done.. Somehow.

Training, documentation, teamwork, and feedback all help to make people smarter (if not less active) and that is where a great deal of effort needs to be applied.

Too rigorous an amount of control in a language or framework doesn't do as much good as everyone thinks. It can often just create huge time overheads, as in the extra syntactic fluff needed to typecast because of Java's static type checking for example.

Affordance

An architecture or a syntax should provide a good context for creating idioms. It should make writing idiomatic code feel right without feeling that you have to jump through hoops. There should be an inherent affordance of the right thing to do.

This puts a lot of faith in the user of the language/ framework or whatever, but there are very successful examples of this. Languages like Ruby and Python (and of course SmallTalk) which allow parametric polymorphism tend to be scary to Java developers, it is, after all, a bit unbridled and wild being able to send messages to any type, but hey, smart lazy people never seem to get into trouble with it.

Perhaps a bit of judicious application of the 4 types would give us an idea who we should be looking out for in our designs and make us realise that some people don't need protection and others just can't be protected.

Next week, why it is better to be rich than ugly.

What do you think? Should we consider the importance of peoples' personalities when designing? What is your favourite anecdote of a stupid, active developer?

I hope you enjoy classifying your collegues!

Resources

Bruce Eckel on The Checked Exception Debate:
Checked Exception

..and The Static Typing Debate:
Static Typing

Helmuth Karl Bernhard Graf von Moltke
Creators of the German Empire

The Lemming Mass Suicide Myth
The Lemming Myth

Talk Back!

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About the Blogger

Jeremy has been designing and developing software for nearly 20 years, as well as teaching its mastery. He is fascinated by all aspects of architecture, design and development, the philosophical, the psychological and the aesthetic. He is currently a principal consultant for Borland Software in their modelling and design space.

This weblog entry is Copyright © 2008 Jeremy Meyer. All rights reserved.

One of the new features of C# 3.0 is the var keyword, which can be used to implicitly declare a variable’s type. For example, instead of declaring the type, you can just write var instead, and the compiler will figure out what type name should be from the value assigned to it:

1.// A variable explicitly declared as a certain type.

2.string name = "Richard";

3. 

4.// A variable implicitly declared as the type being assigned to it.

5.var name = "Richard";

Note that a var isn’t a variant, so it’s quite different from say, a var in javascript. C# vars are strongly typed, so you can’t re-assign them with values of different types:

1.var name = "Richard"

2.name = 62; // error, can't assign an int to a string

Vars were introduced to support the use of anonymous types, which don’t have type names. For example:

1.var me = { Name: "Richard", Age: 22 };

But there’s nothing to stop you from using vars with regular types. In a recent article on codinghorror.com, Jeff Atwood recommends using vars “whenever and wherever it makes [your] code more concise”. Guessing from his examples, this means everywhere you possibly can.

The logic behind this is that it improves your code by eliminating the redundancy of having to write type names twice — once for the variable declaration, and again for a constructor.

There’s always a tradeoff between verbosity and conciseness, but I have an awfully hard time defending the unnecessarily verbose way objects were typically declared in C# and Java.

1.BufferedReader br = new BufferedReader (new FileReader(name));

Who came up with this stuff?

Is there really any doubt what type of the variable br is? Does it help anyone, ever, to require another BufferedReader on the front of that line? This has bothered me for years, but it was an itch I just couldn’t scratch. Until now.

I don’t think he’s right on this one — my initial reaction is that using var everywhere demonstrates laziness by the programmer. And I don’t mean the good sort of laziness which works smarter, not harder, but the bad sort, which can’t be bothered writing proper variable declarations.

Jeff is right though – writing the type name twice does seem a little excessive. However, as Nicholas Paldino notes, the correct way to eliminate this redundancy would be to make the type name on the right hand-side optional, not the left:

While I agree with you that redundancy is not a good thing, the better way to solve this issue would have been to do something like the following:

1.MyObject m = new();

Or if you are passing parameters:

1.Person p = new("FirstName", "LastName");

Where in the creation of a new object, the compiler infers the type from the left-hand side, and not the right.

Microsoft’s C# language reference page for var also warns about the consequences of using var everywhere.

Overuse of var can make source code less readable for others. It is recommended to use var only when it is necessary, that is, when the variable will be used to store an anonymous type or a collection of anonymous types.

In the following example, the balance variable could now theoretically contain an Int32, Int64, Single (float), Double, Decimal, or even a ‘Balance’ object instance, depending on how the GetBalance() method works.

1.var balance = account.GetBalance();

This is rather confusing. Plus, unless you explicitly down cast, vars are always the concrete type being constructed. Let’s go back to Jeff’s BufferedReader example, of which he asks, “is there really any doubt what type of the variable br is?”

1.BufferedReader br = new BufferedReader (new FileReader(name));

Actually, yes there is, because polymorphism is used quite extensively in .NET’s IO libraries. The fact that br is being implemented with a BufferedReader is most likely irrelevant. All we need is something that satisfies a Reader base class contract. So br might actually look like this:

1.Reader br = new BufferedReader (new FileReader(name));

Just because a language allows you to do something, doesn’t mean it’s a good idea to do so. Sometimes new features adapt well to solving problems they weren’t designed for, but this is not one of those situations. Stick to using vars for what they were designed for!

June 21st, 2008 | 40 Comments

Instead of hammering on the differences between
dynamically and statically typed languages, we should
instead strive for a peaceful integration of static and dynamic
aspect in the same language. Static typing where possible, dynamic
typing when needed!

Great article about Session in ASP.NET.

Deliver stunning desktop-class applications in any modern web browser without plugins.

Best Practices for Speeding Up Your Web Site

The Exceptional Performance team has identified a number of best practices for making web pages fast. The list includes 34 best practices divided into 7 categories.

Filter by category:

• Content
• Server
• Cookie
• CSS
• Javascript
• Images
• Mobile
• All

Minimize HTTP Requests

tag: content

80% of the end-user response time is spent on the front-end. Most of this time is tied up in downloading all the components in the page: images, stylesheets, scripts, Flash, etc. Reducing the number of components in turn reduces the number of HTTP requests required to render the page. This is the key to faster pages.

One way to reduce the number of components in the page is to simplify the page's design. But is there a way to build pages with richer content while also achieving fast response times? Here are some techniques for reducing the number of HTTP requests, while still supporting rich page designs.

Combined files are a way to reduce the number of HTTP requests by combining all scripts into a single script, and similarly combining all CSS into a single stylesheet. Combining files is more challenging when the scripts and stylesheets vary from page to page, but making this part of your release process improves response times.

CSS Sprites are the preferred method for reducing the number of image requests. Combine your background images into a single image and use the CSS background-image and background-position properties to display the desired image segment.

Image maps combine multiple images into a single image. The overall size is about the same, but reducing the number of HTTP requests speeds up the page. Image maps only work if the images are contiguous in the page, such as a navigation bar. Defining the coordinates of image maps can be tedious and error prone. Using image maps for navigation is not accessible too, so it's not recommended.

Inline images use the data: URL scheme to embed the image data in the actual page. This can increase the size of your HTML document. Combining inline images into your (cached) stylesheets is a way to reduce HTTP requests and avoid increasing the size of your pages. Inline images are not yet supported across all major browsers.

Reducing the number of HTTP requests in your page is the place to start. This is the most important guideline for improving performance for first time visitors. As described in Tenni Theurer's blog post Browser Cache Usage - Exposed!, 40-60% of daily visitors to your site come in with an empty cache. Making your page fast for these first time visitors is key to a better user experience.

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Use a Content Delivery Network

tag: server

The user's proximity to your web server has an impact on response times. Deploying your content across multiple, geographically dispersed servers will make your pages load faster from the user's perspective. But where should you start?

As a first step to implementing geographically dispersed content, don't attempt to redesign your web application to work in a distributed architecture. Depending on the application, changing the architecture could include daunting tasks such as synchronizing session state and replicating database transactions across server locations. Attempts to reduce the distance between users and your content could be delayed by, or never pass, this application architecture step.

Remember that 80-90% of the end-user response time is spent downloading all the components in the page: images, stylesheets, scripts, Flash, etc. This is the Performance Golden Rule. Rather than starting with the difficult task of redesigning your application architecture, it's better to first disperse your static content. This not only achieves a bigger reduction in response times, but it's easier thanks to content delivery networks.

A content delivery network (CDN) is a collection of web servers distributed across multiple locations to deliver content more efficiently to users. The server selected for delivering content to a specific user is typically based on a measure of network proximity. For example, the server with the fewest network hops or the server with the quickest response time is chosen.

Some large Internet companies own their own CDN, but it's cost-effective to use a CDN service provider, such as Akamai Technologies, Mirror Image Internet, or Limelight Networks. For start-up companies and private web sites, the cost of a CDN service can be prohibitive, but as your target audience grows larger and becomes more global, a CDN is necessary to achieve fast response times. At Yahoo!, properties that moved static content off their application web servers to a CDN improved end-user response times by 20% or more. Switching to a CDN is a relatively easy code change that will dramatically improve the speed of your web site.

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Add an Expires or a Cache-Control Header

tag: server

There are two things in this rule:

• For static components: implement "Never expire" policy by setting far future Expires header
• For dynamic components: use an appropriate Cache-Control header to help the browser with conditional requests

Web page designs are getting richer and richer, which means more scripts, stylesheets, images, and Flash in the page. A first-time visitor to your page may have to make several HTTP requests, but by using the Expires header you make those components cacheable. This avoids unnecessary HTTP requests on subsequent page views. Expires headers are most often used with images, but they should be used on all components including scripts, stylesheets, and Flash components.

Browsers (and proxies) use a cache to reduce the number and size of HTTP requests, making web pages load faster. A web server uses the Expires header in the HTTP response to tell the client how long a component can be cached. This is a far future Expires header, telling the browser that this response won't be stale until April 15, 2010.

      Expires: Thu, 15 Apr 2010 20:00:00 GMT

If your server is Apache, use the ExpiresDefault directive to set an expiration date relative to the current date. This example of the ExpiresDefault directive sets the Expires date 10 years out from the time of the request.

      ExpiresDefault "access plus 10 years"

Keep in mind, if you use a far future Expires header you have to change the component's filename whenever the component changes. At Yahoo! we often make this step part of the build process: a version number is embedded in the component's filename, for example, yahoo_2.0.6.js.

Using a far future Expires header affects page views only after a user has already visited your site. It has no effect on the number of HTTP requests when a user visits your site for the first time and the browser's cache is empty. Therefore the impact of this performance improvement depends on how often users hit your pages with a primed cache. (A "primed cache" already contains all of the components in the page.) We measured this at Yahoo! and found the number of page views with a primed cache is 75-85%. By using a far future Expires header, you increase the number of components that are cached by the browser and re-used on subsequent page views without sending a single byte over the user's Internet connection.

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Gzip Components

tag: server

The time it takes to transfer an HTTP request and response across the network can be significantly reduced by decisions made by front-end engineers. It's true that the end-user's bandwidth speed, Internet service provider, proximity to peering exchange points, etc. are beyond the control of the development team. But there are other variables that affect response times. Compression reduces response times by reducing the size of the HTTP response.

Starting with HTTP/1.1, web clients indicate support for compression with the Accept-Encoding header in the HTTP request.

      Accept-Encoding: gzip, deflate

If the web server sees this header in the request, it may compress the response using one of the methods listed by the client. The web server notifies the web client of this via the Content-Encoding header in the response.

      Content-Encoding: gzip

Gzip is the most popular and effective compression method at this time. It was developed by the GNU project and standardized by RFC 1952. The only other compression format you're likely to see is deflate, but it's less effective and less popular.

Gzipping generally reduces the response size by about 70%. Approximately 90% of today's Internet traffic travels through browsers that claim to support gzip. If you use Apache, the module configuring gzip depends on your version: Apache 1.3 uses mod_gzip while Apache 2.x uses mod_deflate.

There are known issues with browsers and proxies that may cause a mismatch in what the browser expects and what it receives with regard to compressed content. Fortunately, these edge cases are dwindling as the use of older browsers drops off. The Apache modules help out by adding appropriate Vary response headers automatically.

Servers choose what to gzip based on file type, but are typically too limited in what they decide to compress. Most web sites gzip their HTML documents. It's also worthwhile to gzip your scripts and stylesheets, but many web sites miss this opportunity. In fact, it's worthwhile to compress any text response including XML and JSON. Image and PDF files should not be gzipped because they are already compressed. Trying to gzip them not only wastes CPU but can potentially increase file sizes.

Gzipping as many file types as possible is an easy way to reduce page weight and accelerate the user experience.

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Put Stylesheets at the Top

tag: css

While researching performance at Yahoo!, we discovered that moving stylesheets to the document HEAD makes pages appear to be loading faster. This is because putting stylesheets in the HEAD allows the page to render progressively.

Front-end engineers that care about performance want a page to load progressively; that is, we want the browser to display whatever content it has as soon as possible. This is especially important for pages with a lot of content and for users on slower Internet connections. The importance of giving users visual feedback, such as progress indicators, has been well researched and documented. In our case the HTML page is the progress indicator! When the browser loads the page progressively the header, the navigation bar, the logo at the top, etc. all serve as visual feedback for the user who is waiting for the page. This improves the overall user experience.

The problem with putting stylesheets near the bottom of the document is that it prohibits progressive rendering in many browsers, including Internet Explorer. These browsers block rendering to avoid having to redraw elements of the page if their styles change. The user is stuck viewing a blank white page.

The HTML specification clearly states that stylesheets are to be included in the HEAD of the page: "Unlike A, [LINK] may only appear in the HEAD section of a document, although it may appear any number of times." Neither of the alternatives, the blank white screen or flash of unstyled content, are worth the risk. The optimal solution is to follow the HTML specification and load your stylesheets in the document HEAD.

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Put Scripts at the Bottom

tag: javascript

The problem caused by scripts is that they block parallel downloads. The HTTP/1.1 specification suggests that browsers download no more than two components in parallel per hostname. If you serve your images from multiple hostnames, you can get more than two downloads to occur in parallel. While a script is downloading, however, the browser won't start any other downloads, even on different hostnames.

In some situations it's not easy to move scripts to the bottom. If, for example, the script uses document.write to insert part of the page's content, it can't be moved lower in the page. There might also be scoping issues. In many cases, there are ways to workaround these situations.

An alternative suggestion that often comes up is to use deferred scripts. The DEFER attribute indicates that the script does not contain document.write, and is a clue to browsers that they can continue rendering. Unfortunately, Firefox doesn't support the DEFER attribute. In Internet Explorer, the script may be deferred, but not as much as desired. If a script can be deferred, it can also be moved to the bottom of the page. That will make your web pages load faster.

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Avoid CSS Expressions

tag: css

CSS expressions are a powerful (and dangerous) way to set CSS properties dynamically. They're supported in Internet Explorer, starting with version 5. As an example, the background color could be set to alternate every hour using CSS expressions.

      background-color: expression( (new Date()).getHours()%2 ? "#B8D4FF" : "#F08A00" );

As shown here, the expression method accepts a JavaScript expression. The CSS property is set to the result of evaluating the JavaScript expression. The expression method is ignored by other browsers, so it is useful for setting properties in Internet Explorer needed to create a consistent experience across browsers.

The problem with expressions is that they are evaluated more frequently than most people expect. Not only are they evaluated when the page is rendered and resized, but also when the page is scrolled and even when the user moves the mouse over the page. Adding a counter to the CSS expression allows us to keep track of when and how often a CSS expression is evaluated. Moving the mouse around the page can easily generate more than 10,000 evaluations.

One way to reduce the number of times your CSS expression is evaluated is to use one-time expressions, where the first time the expression is evaluated it sets the style property to an explicit value, which replaces the CSS expression. If the style property must be set dynamically throughout the life of the page, using event handlers instead of CSS expressions is an alternative approach. If you must use CSS expressions, remember that they may be evaluated thousands of times and could affect the performance of your page.

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Make JavaScript and CSS External

tag: javascript, css

Many of these performance rules deal with how external components are managed. However, before these considerations arise you should ask a more basic question: Should JavaScript and CSS be contained in external files, or inlined in the page itself?

Using external files in the real world generally produces faster pages because the JavaScript and CSS files are cached by the browser. JavaScript and CSS that are inlined in HTML documents get downloaded every time the HTML document is requested. This reduces the number of HTTP requests that are needed, but increases the size of the HTML document. On the other hand, if the JavaScript and CSS are in external files cached by the browser, the size of the HTML document is reduced without increasing the number of HTTP requests.

The key factor, then, is the frequency with which external JavaScript and CSS components are cached relative to the number of HTML documents requested. This factor, although difficult to quantify, can be gauged using various metrics. If users on your site have multiple page views per session and many of your pages re-use the same scripts and stylesheets, there is a greater potential benefit from cached external files.

Many web sites fall in the middle of these metrics. For these sites, the best solution generally is to deploy the JavaScript and CSS as external files. The only exception where inlining is preferable is with home pages, such as Yahoo!'s front page and My Yahoo!. Home pages that have few (perhaps only one) page view per session may find that inlining JavaScript and CSS results in faster end-user response times.

For front pages that are typically the first of many page views, there are techniques that leverage the reduction of HTTP requests that inlining provides, as well as the caching benefits achieved through using external files. One such technique is to inline JavaScript and CSS in the front page, but dynamically download the external files after the page has finished loading. Subsequent pages would reference the external files that should already be in the browser's cache.

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Reduce DNS Lookups

tag: content

The Domain Name System (DNS) maps hostnames to IP addresses, just as phonebooks map people's names to their phone numbers. When you type www.yahoo.com into your browser, a DNS resolver contacted by the browser returns that server's IP address. DNS has a cost. It typically takes 20-120 milliseconds for DNS to lookup the IP address for a given hostname. The browser can't download anything from this hostname until the DNS lookup is completed.

DNS lookups are cached for better performance. This caching can occur on a special caching server, maintained by the user's ISP or local area network, but there is also caching that occurs on the individual user's computer. The DNS information remains in the operating system's DNS cache (the "DNS Client service" on Microsoft Windows). Most browsers have their own caches, separate from the operating system's cache. As long as the browser keeps a DNS record in its own cache, it doesn't bother the operating system with a request for the record.

Internet Explorer caches DNS lookups for 30 minutes by default, as specified by the DnsCacheTimeout registry setting. Firefox caches DNS lookups for 1 minute, controlled by the network.dnsCacheExpiration configuration setting. (Fasterfox changes this to 1 hour.)

When the client's DNS cache is empty (for both the browser and the operating system), the number of DNS lookups is equal to the number of unique hostnames in the web page. This includes the hostnames used in the page's URL, images, script files, stylesheets, Flash objects, etc. Reducing the number of unique hostnames reduces the number of DNS lookups.

Reducing the number of unique hostnames has the potential to reduce the amount of parallel downloading that takes place in the page. Avoiding DNS lookups cuts response times, but reducing parallel downloads may increase response times. My guideline is to split these components across at least two but no more than four hostnames. This results in a good compromise between reducing DNS lookups and allowing a high degree of parallel downloads.

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Minify JavaScript and CSS

tag: javascript, css

Minification is the practice of removing unnecessary characters from code to reduce its size thereby improving load times. When code is minified all comments are removed, as well as unneeded white space characters (space, newline, and tab). In the case of JavaScript, this improves response time performance because the size of the downloaded file is reduced. Two popular tools for minifying JavaScript code are JSMin and YUI Compressor. The YUI compressor can also minify CSS.

Obfuscation is an alternative optimization that can be applied to source code. It's more complex than minification and thus more likely to generate bugs as a result of the obfuscation step itself. In a survey of ten top U.S. web sites, minification achieved a 21% size reduction versus 25% for obfuscation. Although obfuscation has a higher size reduction, minifying JavaScript is less risky.

In addition to minifying external scripts and styles, inlined <script> and <style> blocks can and should also be minified. Even if you gzip your scripts and styles, minifying them will still reduce the size by 5% or more. As the use and size of JavaScript and CSS increases, so will the savings gained by minifying your code.

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Avoid Redirects

tag: content

Redirects are accomplished using the 301 and 302 status codes. Here's an example of the HTTP headers in a 301 response:

      HTTP/1.1 301 Moved Permanently
      Location: http://example.com/newuri
      Content-Type: text/html

The browser automatically takes the user to the URL specified in the Location field. All the information necessary for a redirect is in the headers. The body of the response is typically empty. Despite their names, neither a 301 nor a 302 response is cached in practice unless additional headers, such as Expires or Cache-Control, indicate it should be. The meta refresh tag and JavaScript are other ways to direct users to a different URL, but if you must do a redirect, the preferred technique is to use the standard 3xx HTTP status codes, primarily to ensure the back button works correctly.

The main thing to remember is that redirects slow down the user experience. Inserting a redirect between the user and the HTML document delays everything in the page since nothing in the page can be rendered and no components can start being downloaded until the HTML document has arrived.

One of the most wasteful redirects happens frequently and web developers are generally not aware of it. It occurs when a trailing slash (/) is missing from a URL that should otherwise have one. For example, going to http://astrology.yahoo.com/astrology results in a 301 response containing a redirect to http://astrology.yahoo.com/astrology/ (notice the added trailing slash). This is fixed in Apache by using Alias or mod_rewrite, or the DirectorySlash directive if you're using Apache handlers.

Connecting an old web site to a new one is another common use for redirects. Others include connecting different parts of a website and directing the user based on certain conditions (type of browser, type of user account, etc.). Using a redirect to connect two web sites is simple and requires little additional coding. Although using redirects in these situations reduces the complexity for developers, it degrades the user experience. Alternatives for this use of redirects include using Alias and mod_rewrite if the two code paths are hosted on the same server. If a domain name change is the cause of using redirects, an alternative is to create a CNAME (a DNS record that creates an alias pointing from one domain name to another) in combination with Alias or mod_rewrite.

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Remove Duplicate Scripts

tag: javascript

It hurts performance to include the same JavaScript file twice in one page. This isn't as unusual as you might think. A review of the ten top U.S. web sites shows that two of them contain a duplicated script. Two main factors increase the odds of a script being duplicated in a single web page: team size and number of scripts. When it does happen, duplicate scripts hurt performance by creating unnecessary HTTP requests and wasted JavaScript execution.

Unnecessary HTTP requests happen in Internet Explorer, but not in Firefox. In Internet Explorer, if an external script is included twice and is not cacheable, it generates two HTTP requests during page loading. Even if the script is cacheable, extra HTTP requests occur when the user reloads the page.

In addition to generating wasteful HTTP requests, time is wasted evaluating the script multiple times. This redundant JavaScript execution happens in both Firefox and Internet Explorer, regardless of whether the script is cacheable.

One way to avoid accidentally including the same script twice is to implement a script management module in your templating system. The typical way to include a script is to use the SCRIPT tag in your HTML page.

      <script type="text/javascript" src="menu_1.0.17.js"></script>

An alternative in PHP would be to create a function called insertScript.

      <?php insertScript("menu.js") ?>

In addition to preventing the same script from being inserted multiple times, this function could handle other issues with scripts, such as dependency checking and adding version numbers to script filenames to support far future Expires headers.

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Configure ETags

tag: server

Entity tags (ETags) are a mechanism that web servers and browsers use to determine whether the component in the browser's cache matches the one on the origin server. (An "entity" is another word a "component": images, scripts, stylesheets, etc.) ETags were added to provide a mechanism for validating entities that is more flexible than the last-modified date. An ETag is a string that uniquely identifies a specific version of a component. The only format constraints are that the string be quoted. The origin server specifies the component's ETag using the ETag response header.

      HTTP/1.1 200 OK
      Last-Modified: Tue, 12 Dec 2006 03:03:59 GMT
      ETag: "10c24bc-4ab-457e1c1f"
      Content-Length: 12195

Later, if the browser has to validate a component, it uses the If-None-Match header to pass the ETag back to the origin server. If the ETags match, a 304 status code is returned reducing the response by 12195 bytes for this example.

      GET /i/yahoo.gif HTTP/1.1
      Host: us.yimg.com
      If-Modified-Since: Tue, 12 Dec 2006 03:03:59 GMT
      If-None-Match: "10c24bc-4ab-457e1c1f"
      HTTP/1.1 304 Not Modified

The problem with ETags is that they typically are constructed using attributes that make them unique to a specific server hosting a site. ETags won't match when a browser gets the original component from one server and later tries to validate that component on a different server, a situation that is all too common on Web sites that use a cluster of servers to handle requests. By default, both Apache and IIS embed data in the ETag that dramatically reduces the odds of the validity test succeeding on web sites with multiple servers.

The ETag format for Apache 1.3 and 2.x is inode-size-timestamp. Although a given file may reside in the same directory across multiple servers, and have the same file size, permissions, timestamp, etc., its inode is different from one server to the next.

IIS 5.0 and 6.0 have a similar issue with ETags. The format for ETags on IIS is Filetimestamp:ChangeNumber. A ChangeNumber is a counter used to track configuration changes to IIS. It's unlikely that the ChangeNumber is the same across all IIS servers behind a web site.

The end result is ETags generated by Apache and IIS for the exact same component won't match from one server to another. If the ETags don't match, the user doesn't receive the small, fast 304 response that ETags were designed for; instead, they'll get a normal 200 response along with all the data for the component. If you host your web site on just one server, this isn't a problem. But if you have multiple servers hosting your web site, and you're using Apache or IIS with the default ETag configuration, your users are getting slower pages, your servers have a higher load, you're consuming greater bandwidth, and proxies aren't caching your content efficiently. Even if your components have a far future Expires header, a conditional GET request is still made whenever the user hits Reload or Refresh.

If you're not taking advantage of the flexible validation model that ETags provide, it's better to just remove the ETag altogether. The Last-Modified header validates based on the component's timestamp. And removing the ETag reduces the size of the HTTP headers in both the response and subsequent requests. This Microsoft Support article describes how to remove ETags. In Apache, this is done by simply adding the following line to your Apache configuration file:

      FileETag none

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Make Ajax Cacheable

tag: content

One of the cited benefits of Ajax is that it provides instantaneous feedback to the user because it requests information asynchronously from the backend web server. However, using Ajax is no guarantee that the user won't be twiddling his thumbs waiting for those asynchronous JavaScript and XML responses to return. In many applications, whether or not the user is kept waiting depends on how Ajax is used. For example, in a web-based email client the user will be kept waiting for the results of an Ajax request to find all the email messages that match their search criteria. It's important to remember that "asynchronous" does not imply "instantaneous".

To improve performance, it's important to optimize these Ajax responses. The most important way to improve the performance of Ajax is to make the responses cacheable, as discussed in Add an Expires or a Cache-Control Header. Some of the other rules also apply to Ajax:

• Gzip Components
  
• Reduce DNS Lookups
  
• Minify JavaScript
  
• Avoid Redirects
  
• Configure ETags
  

Let's look at an example. A Web 2.0 email client might use Ajax to download the user's address book for autocompletion. If the user hasn't modified her address book since the last time she used the email web app, the previous address book response could be read from cache if that Ajax response was made cacheable with a future Expires or Cache-Control header. The browser must be informed when to use a previously cached address book response versus requesting a new one. This could be done by adding a timestamp to the address book Ajax URL indicating the last time the user modified her address book, for example, &t=1190241612. If the address book hasn't been modified since the last download, the timestamp will be the same and the address book will be read from the browser's cache eliminating an extra HTTP roundtrip. If the user has modified her address book, the timestamp ensures the new URL doesn't match the cached response, and the browser will request the updated address book entries.

Even though your Ajax responses are created dynamically, and might only be applicable to a single user, they can still be cached. Doing so will make your Web 2.0 apps faster.

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Flush the Buffer Early

tag: server

When users request a page, it can take anywhere from 200 to 500ms for the backend server to stitch together the HTML page. During this time, the browser is idle as it waits for the data to arrive. In PHP you have the function flush(). It allows you to send your partially ready HTML response to the browser so that the browser can start fetching components while your backend is busy with the rest of the HTML page. The benefit is mainly seen on busy backends or light frontends.

A good place to consider flushing is right after the HEAD because the HTML for the head is usually easier to produce and it allows you to include any CSS and JavaScript files for the browser to start fetching in parallel while the backend is still processing.

Example:

      ... 
    </head>
    <?php flush(); ?>
    <body>
      ... 

Yahoo! search pioneered research and real user testing to prove the benefits of using this technique.

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Use GET for AJAX Requests

tag: server

The Yahoo! Mail team found that when using XMLHttpRequest, POST is implemented in the browsers as a two-step process: sending the headers first, then sending data. So it's best to use GET, which only takes one TCP packet to send (unless you have a lot of cookies). The maximum URL length in IE is 2K, so if you send more than 2K data you might not be able to use GET.

An interesting side affect is that POST without actually posting any data behaves like GET. Based on the HTTP specs, GET is meant for retrieving information, so it makes sense (semantically) to use GET when you're only requesting data, as opposed to sending data to be stored server-side.

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Post-load Components

tag: content

You can take a closer look at your page and ask yourself: "What's absolutely required in order to render the page initially?". The rest of the content and components can wait.

JavaScript is an ideal candidate for splitting before and after the onload event. For example if you have JavaScript code and libraries that do drag and drop and animations, those can wait, because dragging elements on the page comes after the initial rendering. Other places to look for candidates for post-loading include hidden content (content that appears after a user action) and images below the fold.

Tools to help you out in your effort: YUI Image Loader allows you to delay images below the fold and the YUI Get utility is an easy way to include JS and CSS on the fly. For an example in the wild take a look at Yahoo! Home Page with Firebug's Net Panel turned on.

It's good when the performance goals are inline with other web development best practices. In this case, the idea of progressive enhancement tells us that JavaScript, when supported, can improve the user experience but you have to make sure the page works even without JavaScript. So after you've made sure the page works fine, you can enhance it with some post-loaded scripts that give you more bells and whistles such as drag and drop and animations.

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Preload Components

tag: content

Preload may look like the opposite of post-load, but it actually has a different goal. By preloading components you can take advantage of the time the browser is idle and request components (like images, styles and scripts) you'll need in the future. This way when the user visits the next page, you could have most of the components already in the cache and your page will load much faster for the user.

There are actually several types of preloading:

• Unconditional preload - as soon as onload fires, you go ahead and fetch some extra components. Check google.com for an example of how a sprite image is requested onload. This sprite image is not needed on the google.com homepage, but it is needed on the consecutive search result page.
• Conditional preload - based on a user action you make an educated guess where the user is headed next and preload accordingly. On search.yahoo.com you can see how some extra components are requested after you start typing in the input box.
• Anticipated preload - preload in advance before launching a redesign. It often happens after a redesign that you hear: "The new site is cool, but it's slower than before". Part of the problem could be that the users were visiting your old site with a full cache, but the new one is always an empty cache experience. You can mitigate this side effect by preloading some components before you even launched the redesign. Your old site can use the time the browser is idle and request images and scripts that will be used by the new site

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Reduce the Number of DOM Elements

tag: content

A complex page means more bytes to download and it also means slower DOM access in JavaScript. It makes a difference if you loop through 500 or 5000 DOM elements on the page when you want to add an event handler for example.

A high number of DOM elements can be a symptom that there's something that should be improved with the markup of the page without necessarily removing content. Are you using nested tables for layout purposes? Are you throwing in more <div>s only to fix layout issues? Maybe there's a better and more semantically correct way to do your markup.

A great help with layouts are the YUI CSS utilities: grids.css can help you with the overall layout, fonts.css and reset.css can help you strip away the browser's defaults formatting. This is a chance to start fresh and think about your markup, for example use <div>s only when it makes sense semantically, and not because it renders a new line.

The number of DOM elements is easy to test, just type in Firebug's console:
document.getElementsByTagName('*').length

And how many DOM elements are too many? Check other similar pages that have good markup. For example the Yahoo! Home Page is a pretty busy page and still under 700 elements (HTML tags).

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Split Components Across Domains

tag: content

Splitting components allows you to maximize parallel downloads. Make sure you're using not more than 2-4 domains because of the DNS lookup penalty. For example, you can host your HTML and dynamic content on www.example.org and split static components between static1.example.org and static2.example.org

For more information check "Maximizing Parallel Downloads in the Carpool Lane" by Tenni Theurer and Patty Chi.

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Minimize the Number of iframes

tag: content

Iframes allow an HTML document to be inserted in the parent document. It's important to understand how iframes work so they can be used effectively.

<iframe> pros:

• Helps with slow third-party content like badges and ads
• Security sandbox
• Download scripts in parallel

<iframe> cons:

• Costly even if blank
• Blocks page onload
• Non-semantic

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No 404s

tag: content

HTTP requests are expensive so making an HTTP request and getting a useless response (i.e. 404 Not Found) is totally unnecessary and will slow down the user experience without any benefit.

Some sites have helpful 404s "Did you mean X?", which is great for the user experience but also wastes server resources (like database, etc). Particularly bad is when the link to an external JavaScript is wrong and the result is a 404. First, this download will block parallel downloads. Next the browser may try to parse the 404 response body as if it were JavaScript code, trying to find something usable in it.

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Reduce Cookie Size

tag: cookie

HTTP cookies are used for a variety of reasons such as authentication and personalization. Information about cookies is exchanged in the HTTP headers between web servers and browsers. It's important to keep the size of cookies as low as possible to minimize the impact on the user's response time.

For more information check "When the Cookie Crumbles" by Tenni Theurer and Patty Chi. The take-home of this research:

• Eliminate unnecessary cookies
• Keep cookie sizes as low as possible to minimize the impact on the user response time
• Be mindful of setting cookies at the appropriate domain level so other sub-domains are not affected
• Set an Expires date appropriately. An earlier Expires date or none removes the cookie sooner, improving the user response time

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Use Cookie-free Domains for Components

tag: cookie

When the browser makes a request for a static image and sends cookies together with the request, the server doesn't have any use for those cookies. So they only create network traffic for no good reason. You should make sure static components are requested with cookie-free requests. Create a subdomain and host all your static components there.

If your domain is www.example.org, you can host your static components on static.example.org. However, if you've already set cookies on the top-level domain example.org as opposed to www.example.org, then all the requests to static.example.org will include those cookies. In this case, you can buy a whole new domain, host your static components there, and keep this domain cookie-free. Yahoo! uses yimg.com, YouTube uses ytimg.com, Amazon uses images-amazon.com and so on.

Another benefit of hosting static components on a cookie-free domain is that some proxies might refuse to cache the components that are requested with cookies. On a related note, if you wonder if you should use example.org or www.example.org for your home page, consider the cookie impact. Omitting www leaves you no choice but to write cookies to *.example.org, so for performance reasons it's best to use the www subdomain and write the cookies to that subdomain.

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Minimize DOM Access

tag: javascript

Accessing DOM elements with JavaScript is slow so in order to have a more responsive page, you should:

• Cache references to accessed elements
• Update nodes "offline" and then add them to the tree
• Avoid fixing layout with JavaScript

For more information check the YUI theatre's "High Performance Ajax Applications" by Julien Lecomte.

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Develop Smart Event Handlers

tag: javascript

Sometimes pages feel less responsive because of too many event handlers attached to different elements of the DOM tree which are then executed too often. That's why using event delegation is a good approach. If you have 10 buttons inside a div, attach only one event handler to the div wrapper, instead of one handler for each button. Events bubble up so you'll be able to catch the event and figure out which button it originated from.

You also don't need to wait for the onload event in order to start doing something with the DOM tree. Often all you need is the element you want to access to be available in the tree. You don't have to wait for all images to be downloaded. DOMContentLoaded is the event you might consider using instead of onload, but until it's available in all browsers, you can use the YUI Event utility, which has an onAvailable method.

For more information check the YUI theatre's "High Performance Ajax Applications" by Julien Lecomte.

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Choose <link> over @import

tag: css

One of the previous best practices states that CSS should be at the top in order to allow for progressive rendering.

In IE @import behaves the same as using <link> at the bottom of the page, so it's best not to use it.

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Avoid Filters

tag: css

The IE-proprietary AlphaImageLoader filter aims to fix a problem with semi-transparent true color PNGs in IE versions < 7. The problem with this filter is that it blocks rendering and freezes the browser while the image is being downloaded. It also increases memory consumption and is applied per element, not per image, so the problem is multiplied.

The best approach is to avoid AlphaImageLoader completely and use gracefully degrading PNG8 instead, which are fine in IE. If you absolutely need AlphaImageLoader, use the underscore hack _filter as to not penalize your IE7+ users.

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Optimize Images

tag: images

After a designer is done with creating the images for your web page, there are still some things you can try before you FTP those images to your web server.

• You can check the GIFs and see if they are using a palette size corresponding to the number of colors in the image. Using imagemagick it's easy to check using
  identify -verbose image.gif
  When you see an image useing 4 colors and a 256 color "slots" in the palette, there is room for improvement.
• Try converting GIFs to PNGs and see if there is a saving. More often than not, there is. Developers often hesitate to use PNGs due to the limited support in browsers, but this is now a thing of the past. The only real problem is alpha-transparency in true color PNGs, but then again, GIFs are not true color and don't support variable transparency either. So anything a GIF can do, a palette PNG (PNG8) can do too (except for animations). This simple imagemagick command results in totally safe-to-use PNGs:
  convert image.gif image.png
  "All we are saying is: Give PiNG a Chance!"
• Run pngcrush (or any other PNG optimizer tool) on all your PNGs. Example:
  pngcrush image.png -rem alla -reduce -brute result.png
• Run jpegtran on all your JPEGs. This tool does lossless JPEG operations such as rotation and can also be used to optimize and remove comments and other useless information (such as EXIF information) from your images.
  jpegtran -copy none -optimize -perfect src.jpg dest.jpg

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Optimize CSS Sprites

tag: images

• Arranging the images in the sprite horizontally as opposed to vertically usually results in a smaller file size.
• Combining similar colors in a sprite helps you keep the color count low, ideally under 256 colors so to fit in a PNG8.
• "Be mobile-friendly" and don't leave big gaps between the images in a sprite. This doesn't affect the file size as much but requires less memory for the user agent to decompress the image into a pixel map. 100x100 image is 10 thousand pixels, where 1000x1000 is 1 million pixels

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Don't Scale Images in HTML

tag: images

Don't use a bigger image than you need just because you can set the width and height in HTML. If you need

then your image (mycat.jpg) should be 100x100px rather than a scaled down 500x500px image.

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Make favicon.ico Small and Cacheable

tag: images

The favicon.ico is an image that stays in the root of your server. It's a necessary evil because even if you don't care about it the browser will still request it, so it's better not to respond with a 404 Not Found. Also since it's on the same server, cookies are sent every time it's requested. This image also interferes with the download sequence, for example in IE when you request extra components in the onload, the favicon will be downloaded before these extra components.

So to mitigate the drawbacks of having a favicon.ico make sure:

• It's small, preferably under 1K.
• Set Expires header with what you feel comfortable (since you cannot rename it if you decide to change it). You can probably safely set the Expires header a few months in the future. You can check the last modified date of your current favicon.ico to make an informed decision.

Imagemagick can help you create small favicons

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Keep Components under 25K

tag: mobile

This restriction is related to the fact that iPhone won't cache components bigger than 25K. Note that this is the uncompressed size. This is where minification is important because gzip alone may not be sufficient.

For more information check "Performance Research, Part 5: iPhone Cacheability - Making it Stick" by Wayne Shea and Tenni Theurer.

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Pack Components into a Multipart Document

tag: mobile

Packing components into a multipart document is like an email with attachments, it helps you fetch several components with one HTTP request (remember: HTTP requests are expensive). When you use this technique, first check if the user agent supports it (iPhone does not).

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It's based on Microsoft Public License, developers can freely use and redistribute it in commercial or open source projects.