You are previewing High Performance Web Sites.

High Performance Web Sites

Cover of High Performance Web Sites by Steve Souders Published by O'Reilly Media, Inc.
  1. High Performance Web Sites
    1. SPECIAL OFFER: Upgrade this ebook with O’Reilly
    2. Praise for High Performance Web Sites
    3. Foreword
    4. Preface
      1. How This Book Is Organized
      2. Conventions Used in This Book
      3. Code Examples
      4. Comments and Questions
      5. Safari® Books Online
      6. Acknowledgments
    5. 1. The Importance of Frontend Performance
      1. Tracking Web Page Performance
      2. Where Does the Time Go?
      3. The Performance Golden Rule
    6. 2. HTTP Overview
      1. Compression
      2. Conditional GET Requests
      3. Expires
      4. Keep-Alive
      5. There's More
    7. 3. Rule 1: Make Fewer HTTP Requests
      1. Image Maps
      2. CSS Sprites
      3. Inline Images
      4. Combined Scripts and Stylesheets
      5. Conclusion
    8. 4. Rule 2: Use a Content Delivery Network
      1. Content Delivery Networks
      2. The Savings
    9. 5. Rule 3: Add an Expires Header
      1. Expires Header
      2. Max-Age and mod_expires
      3. Empty Cache vs. Primed Cache
      4. More Than Just Images
      5. Revving Filenames
      6. Examples
    10. 6. Rule 4: Gzip Components
      1. How Compression Works
      2. What to Compress
      3. The Savings
      4. Configuration
      5. Proxy Caching
      6. Edge Cases
      7. Gzip in Action
    11. 7. Rule 5: Put Stylesheets at the Top
      1. Progressive Rendering
      2. sleep.cgi
      3. Blank White Screen
      4. Flash of Unstyled Content
      5. What's a Frontend Engineer to Do?
    12. 8. Rule 6: Put Scripts at the Bottom
      1. Problems with Scripts
      2. Parallel Downloads
      3. Scripts Block Downloads
      4. Worst Case: Scripts at the Top
      5. Best Case: Scripts at the Bottom
      6. Putting It in Perspective
    13. 9. Rule 7: Avoid CSS Expressions
      1. Updating Expressions
      2. Working Around the Problem
      3. Conclusion
    14. 10. Rule 8: Make JavaScript and CSS External
      1. Inline vs. External
      2. Typical Results in the Field
      3. Home Pages
      4. The Best of Both Worlds
    15. 11. Rule 9: Reduce DNS Lookups
      1. DNS Caching and TTLs
      2. The Browser's Perspective
      3. Reducing DNS Lookups
    16. 12. Rule 10: Minify JavaScript
      1. Minification
      2. Obfuscation
      3. The Savings
      4. Examples
      5. Icing on the Cake
    17. 13. Rule 11: Avoid Redirects
      1. Types of Redirects
      2. How Redirects Hurt Performance
      3. Alternatives to Redirects
    18. 14. Rule 12: Remove Duplicate Scripts
      1. Duplicate Scripts—They Happen
      2. Duplicate Scripts Hurt Performance
      3. Avoiding Duplicate Scripts
    19. 15. Rule 13: Configure ETags
      1. What's an ETag?
      2. The Problem with ETags
      3. ETags: Use 'Em or Lose 'Em
      4. ETags in the Real World
    20. 16. Rule 14: Make Ajax Cacheable
      1. Web 2.0, DHTML, and Ajax
      2. Asynchronous = Instantaneous?
      3. Optimizing Ajax Requests
      4. Caching Ajax in the Real World
    21. 17. Deconstructing 10 Top Sites
      1. Page Weight, Response Time, YSlow Grade
      2. How the Tests Were Done
      3. Amazon
      4. AOL
      5. CNN
      6. eBay
      7. Google
      8. MSN
      9. MySpace
      10. Wikipedia
      11. Yahoo!
      12. YouTube
    22. Index
    23. About the Author
    24. Colophon
    25. SPECIAL OFFER: Upgrade this ebook with O’Reilly
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Alternatives to Redirects

Redirects are an easy way to solve many problems, but it's better to use alternative solutions that don't slow down page loading. The following sections discuss some of the typical situations in which redirects are used, and alternatives that are better for your users.

Missing Trailing Slash

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, the redirect illustrated in Figure 13-1 was generated by going to http://astrology.yahoo.com/astrology. This request results in a 301 response containing a redirect to http://astrology.yahoo.com/astrology/. The only difference is the addition of a trailing slash.

There are good reasons for sending a redirect when the trailing slash is missing: it allows autoindexing (going to the index.html by default) and makes it possible to retrieve URLs in the page that are relative to the current directory (e.g., logo.gif). However, many popular web pages don't rely on autoindexing, instead relying on specific URLs and handlers. Additionally, URLs are often relative to the root and not to the current directory.

Note that a redirect does not happen if the trailing slash is missing after the hostname. For example, http://www.yahoo.com does not generate a redirect. However, the resultant URL seen in your browser does contain the trailing slash: http://www.yahoo.com/. The automatic ...

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