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