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| <html> |
| <head> |
| <meta name="viewport" content="width=device-width, initial-scale=1"> |
| <title>Optimizing For Bandwidth</title> |
| <link rel="stylesheet" href="doc.css"> |
| </head> |
| <body> |
| <!--#include virtual="_header.html" --> |
| |
| |
| <div id=content> |
| <h1>Optimizing For Bandwidth</h1> <p> |
| PageSpeed's default <code>RewriteLevel</code> of |
| <a href="config_filters#level">CoreFilters</a> |
| is designed to reduce latency, incurring a small risk of page breakage. |
| A related goal, bandwidth reduction, can be achieved with close to zero |
| risk of web-site breakage:</p> |
| <dl> |
| <dt>Apache:<dd><pre class="prettyprint"> |
| ModPagespeedRewriteLevel OptimizeForBandwidth</pre> |
| <dt>Nginx:<dd><pre class="prettyprint"> |
| pagespeed RewriteLevel OptimizeForBandwidth;</pre> |
| </dl> |
| <p> |
| This option is suitable for use in a root configuration at a |
| hosting service, CDN, or multi-site setup, in conjunction with |
| <a href="configuration#virtual-hosts">InheritVhostConfig</a>. |
| In this mode, PageSpeed does not alter HTML at all. It compresses |
| and transcodes images <a href="system#ipro">in place</a>, and minifies |
| JavaScript and CSS. By avoiding changes to URL syntax and to HTML, the |
| potential problem of user-written JavaScript encountering unexpected |
| DOM elements is elimimated. There is still latency benefit due to the |
| reduced size of resources, as well as substantial bandwidth reduction. |
| </p> |
| <h2 id="savings">Bandwidth Savings</h2> |
| <p> |
| The bandwidth savings resulting from this option are, of course, |
| dependent on the source site. Our tests with the default |
| settings for OptimizeForBandwidth indicate an average bandwidth |
| reduction of roughly 37% over the content of 1000 large web sites with |
| a client that is capable of displaying webp images, and 25% improvement |
| with older clients. |
| </p> |
| <h2 id="adding_options">Adding Additional Options</h2> |
| <p> |
| Additional latency optimizations that modify HTML can be layered on |
| top of <code>OptimizeForBandwidth</code> by enabling additional |
| filters, and altering the <a href="config_filters#preserveurls">Preserve |
| URL settings</a> for CSS, images, or JavaScript. For example, to set |
| up a shared hosting server with OptimizeForBandwidth in the root, but |
| where individual sites have added |
| <a href="filter-js-inline">inline_javascript</a>, |
| <a href="filter-lazyload-images">lazyload_images</a> and |
| <a href="filter-prioritize-critical-css">prioritize_critical_css</a>, |
| or simply turned on <a href="config_filters#level">CoreFilters</a>, |
| the following pagespeed.conf fragment may be used: |
| </p> |
| <dl> |
| <dt>Apache:</dt> |
| <dd> |
| <pre> |
| ModPagespeedInheritVHostConfig on |
| ModPagespeedRewriteLevel OptimizeForBandwidth |
| <VirtualHost *:80> |
| ServerName prioritize_above_the_fold.example.com |
| ModPagespeedEnableFilters inline_javascript,prioritize_critical_css,inline_preview_images |
| </VirtualHost> |
| <VirtualHost *:80> |
| ServerName preserve_css_urls_off.example.com |
| ModPagespeedCssPreserveURLs off |
| </Directory> |
| <VirtualHost *:80> |
| ServerName core.example.com |
| ModPagespeedRewriteLevel CoreFilters |
| </Directory></pre> |
| </dd> |
| <dt>Nginx:</dt> |
| <dd> |
| <pre> |
| pagespeed RewriteLevel OptimizeForBandwidth; |
| server { |
| server_name prioritize_above_the_fold.example.com |
| pagespeed EnableFilters inline_javascript,prioritize_critical_css,inline_preview_images |
| } |
| server { |
| server_name preserve_css_urls_off.example.com |
| pagespeed CssPreserveURLs off |
| } |
| server { |
| server_name core.example.com |
| pagespeed RewriteLevel CoreFilters |
| }</pre> |
| </dd> |
| </dl> |
| <p> |
| In version 1.9.32.1 and later, <a href="system#ipro">In Place |
| Resource Optimization</a> is enabled by default. In earlier versions, |
| turning on OptimizeForBandwidth automatically enables In Place |
| Resource Optimization to optimize the resources without needing |
| to change their URLs. In these earlier versions, when a VirtualHost |
| overrides the <code>RewriteLevel</code> to <code>CoreFilers</code>, that |
| turns off In Place Resource Optimization, but it can be re-enabled |
| explicitly:</p> |
| <dl> |
| <dt>Apache:<dd><pre class="prettyprint" |
| >ModPagespeedInPlaceResourceOptimization on</pre> |
| <dt>Nginx:<dd><pre class="prettyprint" |
| >pagespeed InPlaceResourceOptimization on;</pre> |
| </dl> |
| </div> |
| <!--#include virtual="_footer.html" --> |
| </body> |
| </html> |
