Website optimization with request reduce

Website Optimization with RequestReduce Matt Wrock 10/26/2011

Current Trends in Web Page Size And Request CountsFrom http://httparchive.org

Web Performance PredictorsFrom http://httparchive.org

Why is this important?• PLT has a direct impact on traffic and conversions• Yahoo found that 400ms equaled a 5 – 9% drop in full page traffic• Google takes speed into account in search rankings

What is RequestReduce• Applies common client side performance best practices so that you don’t have to – CSS and Javascript Merge and Minification – CSS Import expansion – Automatic Sprite Generation – Sprite PNG Optimization – Cache Header Generation – Supports multi server content synchronization – Supports CDN hosts

Side by Side Comparison (Without RequestReduce)

Side by Side Comparison (With RequestReduce)

The Competition

Features Unique to RequestReduce• Reduces on the fly instead of at build time – Can reduce Dynamic css and javascript• Unobtrusive: Does not require you to change your code, configuration or file structure.• Works with all asp.net technologies (MVC/Web Forms/Razor)• Pulls resources via HTTP – can reduce distributed and third party resources.• Synchronizes content across multiple servers

Why not just make this part of the build process?• Does not work or difficult to integrate with dynamic or external css and javascript• Unusually requires new static resource to be manually “plugged in”• Easy to forget or overlook integrating new content• RequestReduce is designed to be “dropped” in to any running app with minimal customization or consideration of that App’s design

RequestReduce: How does it work?• Filter’s the response looking for <HEAD/> and <SCRIPT/> tags – Derives from Stream and is attached to the Response stream of any text/html resource – Extracts URLs from Link hrefs and script src – Ignore CSS and Script inside conditional comments – Ignore script URLs included in black list (google and MS jquery CDN included by default) – Creates a key from concatenated urls that can be merged together – Queries a dictionary for the existence of that key

The Reducing Process

Sprite Generation• All CSS is scanned for classes containing a background image.• Each class is treated as an autonomous unit. No inheritance awareness.• Cannot currently sprite: – Repeating images – Images positioned with non pixel units or a percentage unit > 0. – Images with no explicit horizontal dimension (padding + width)

Sprite Image Processing• Both Lossy and Lossless compression is applied.• Silverlight Code Gallery before any spriting is applied has a spritable payload size of 18k.• After initial sprite generation: 27k• Why? It’s a 32bit PNG• Need to quantize down to 8 bit.• Standard C based quantizers had inadequate quality

Developing nQuant• Images quantized using pngquant.exe were often coming out with distorted colors• Tried to find Free OSS quantizers. Either license was not friendly or the they were code samples that were not alpha aware and had horrid quality.• Found a C based algorithm converted to C# that was extremely high quality but not alpha aware.• Tokk me about a month to come up with the formulas that supported the alpha layers and the result is nQuant (available on codeplex).• Silverlight spright optimized to 10.6k after quantization.• Use optipng for final lossless compression to get to 9k.

Sprite Sizing Limits• RequestReduce continues to add images to a sprite until the image size exceeds 50k.• OR until there are over 5000 unique colors in the sprite – Mitigates poor quantization output.• Threshold can be safely increased with JPGs.• Lots of room for future experimantation here

Migration issues with sprites• Depending on original CSS structure, can sprite most images with no editing or dramatically distort the rendering.• Like every thing else, this feature can be turned off.• I have assisted Galleries, Forums, Profile and Search to convert the CSS to be RequestReduce friendly.

CSS Sprite change example• Old CSS:img.alert,img.answer,img.answered,img.ask{ background: url(http://i1.social.s-msft.com/contentservice/c2afadb0-5d34-489a-bf31-9f5c011d3cd4/icon_strip_windows.png) no-repeat !important;Width: 20px;}img.ask { background-position: -100px 0;}img.answer { background-position: -120px 0;}img.alert { background-position: -140px 0;}• Merge image with position into one class.

Serving the Reduced Resources• All reduced content is cached and managed by RequestReduce• The following caching headers are applied: – Cache-control: public (ensures resources will be cached on proxies and CDNs) – Expires: 360 days from serving (over a year would violate http RFC) – Etag: “<32byte hash of file contents>” ensures Etag is automatically invalidated upon content change.

Reduced Content caching• RequestReduce Supports two caching modes: – Simple file system cache • This can be any UNC path including a remote share or centralized image server • This mode is ideal for individual dev environments due to its simplicity. • On app startup, the file names of the file cache are read and keyed in memory so that content does not have to be reprocessed. – SQL Server caching…

Caching across multiple servers• The Sql Server based cache is ideal for multi server test and production environments.• All reduced content is initially saved to a sql table

Content Changing and Flushing• Content is automatically flushed and queued for reprocessing when CSS or Javascript Urls change.• Changes that do not result in a url change will require a flush in order to be seen. To flush content from a file based settingm you can wither delete the RequestReduce directory or issue a flush explicitly via http://<app>/RequestReduceContent/flush• Sql Servers can also call the flush url but it may take up to 5 minutes for all servers to sync.• Deleting the data directory in a webserver running against a sql based cache, will NOT clear the cache.

Troubleshooting• Normal dev work may want to have RequestReduce turned off.• Appending any url with rrfilter=disabled effectively shuts down the response filter for the current request. This is a good technique to determine if RequestReduce is responsible for page defects

Optimizing• Request can often perform better based on dev practices: – Maker sure background images are sprite friendly – Use background images for commonly used foreground images – Group cachable javascript together and preferably at the bottom of the page if you can

So many more possibilities• Foreground image spriting• Optimize non sprites• Externalize inline styles and scripts• Asynchronously load CSS• Support defered javascript execution• Exploit perf optimizations specific to the browser of the incoming request• Make the processing build friendly and expand extension points

Resources• Project home page: http://www.RequestReduce.com• Source Code: https://github.com/mwrock/RequestReduce I take pull requests• Detailed and organized Wiki documentation: https://github.com/mwrock/RequestReduce/wiki• Bug reporting and feature requests: https://github.com/mwrock/RequestReduce/issue

Website optimization with request reduce

by Matt Wrock on Oct 26, 2011

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