224 lines
14 KiB
HTML
224 lines
14 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="topic" />
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<meta name="DC.Title" content="Triggered cache manager for HTTP Server" />
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<meta name="abstract" content="This topic provides information about the triggered cache manager, page assembly, and wrappers." />
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<meta name="description" content="This topic provides information about the triggered cache manager, page assembly, and wrappers." />
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<meta name="DC.Relation" scheme="URI" content="rzaieconcepts.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2002,2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2002,2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rzaietriggeredcacheman" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Triggered cache manager for HTTP Server</title>
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</head>
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<body id="rzaietriggeredcacheman"><a name="rzaietriggeredcacheman"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Triggered cache manager for HTTP Server</h1>
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<div><p>This topic provides information about the triggered cache manager,
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page assembly, and wrappers.</p>
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<div class="important"><span class="importanttitle">Important:</span> Information
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for this topic supports the latest PTF levels for HTTP Server for i5/OS .
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It is recommended that you install the latest PTFs to upgrade to the latest
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level of the HTTP Server for i5/OS. Some of the topics documented here are
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not available prior to this update. See <a href="http://www-03.ibm.com/servers/eserver/iseries/software/http/services/service.html" target="_blank">http://www.ibm.com/servers/eserver/iseries/software/http/services/service.htm</a> <img src="www.gif" alt="Link outside Information Center" /> for more information. </div>
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<p>The triggered cache manager (TCM) function provides a means to manage cached
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copies of static and dynamically produced Web pages including those generated
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by CGI programs, Net.Data<sup>®</sup>, or Java™ servlets. The triggered cache manager
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function does not provide a cache, but rather a cache content manager. Web
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pages are actually cached in such places as local file systems, proxy servers,
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or caching network routers. When used in conjunction with an application trigger,
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the triggered cache manager function keeps caches synchronized with the most
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current data while reducing the frequency of unnecessary dynamic page generation
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and cache synchronization. See <a href="rzaietrigger.htm">Trigger messages for triggered cache manager on HTTP Server (powered by Apache)</a> for
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more information.</p>
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<p>These Web pages can consist of a single object or they can consist of several
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objects (or page fragments). Dynamically produced Web pages that embed page
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fragments are updated anytime an embedded page fragment changes. </p>
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<p>For example, several Web pages are constructed by a Java servlet using
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data extracted from a DB2<sup>®</sup> database. These Web pages are in turn cached in several
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caching network routers. Web pages are served from the network router caches
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rather than from the HTTP server running the Java servlet. When the database
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data is changed, an application sends a trigger message to the triggered cache
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manager function. Through the use of object dependency graphs, the triggered
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cache manager function determines which Web pages need to be updated. The
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triggered cache manager function then requests new versions of each affected
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Web page from the Java servlet and updates the cached copies in the caching
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network routers. </p>
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<p>In this example, the Web site performance is greatly increased by serving
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cached copies of dynamically produced Web pages rather than serving newly
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generated Web pages for each request. The Web site consistency and performance
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is again increased by using an application trigger, with the triggered cache
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manager function, to update cached Web pages only when underlying data changes.
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This avoids unnecessary and costly cache updates and synchronization. </p>
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<p>The triggered cache manager function is most effective for a Web site that
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has a large number of requests for content that is somewhat constant, but
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with variables that change frequently. An example of this might be a Web site
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that serves an on-line catalog that contains price and inventory information
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(the product information is static, but the price and inventory information
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changes frequently). One of IBM's first uses of the triggered cache manager
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function was to drive the 1996 Winter Olympic Games Web site. </p>
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<div class="section" id="rzaietriggeredcacheman__page"><a name="rzaietriggeredcacheman__page"><!-- --></a><h4 class="sectiontitle">Page assembly</h4><p>Often, advanced Web sites
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contain information that appears on more than one page. If the information
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changes, all of the pages with that information need to be updated. There
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are several potentially difficult problems associated with this: </p>
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<ul><li>It can be extremely difficult to find and update all affected pages, especially
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as a Web site grows in complexity. </li>
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<li>Information with a tendency to change also has a tendency to be expensive
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to maintain; for example, database activity might be required to effect an
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update. </li>
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</ul>
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<p>If a Web site's pages can be composed from partial HTML fragments.
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Each fragment is unique and any page that contains its information acquires
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it by embedding the fragment. This can lead to more flexible, diverse, and
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complex Web sites. </p>
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<p>The trigger cache manager function provides a
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way to assemble Web pages from a set of fragments. If a fragment changes,
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the author of the fragment needs only to publish that fragment; the triggered
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cache manager finds all the affected pages (data sources), rebuilds them,
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and copies the updated pages to the configured delivery locations (cache targets).
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</p>
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<p>To take advantage of this facility, HTML segments must indicate which
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other fragments are to be embedded. This is done with a simple tag very similar
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to Server Side Includes (SSI). These tags are used for two purposes: </p>
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<ul><li>To determine the dependency relationships among HTML fragments (dependency
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parsing). </li>
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<li>To physically construct pages from the fragments (page assembly). </li>
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</ul>
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<p>A publish trigger handler is used to accomplish this task. </p>
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<p>The
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tag used to specify that a fragment is to be included is specified in HTML
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as follows. The keyword <em>%fragment</em> is chosen to avoid conflicts with
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SSI. </p>
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<pre class="block"><!-- %fragment (/source-name, /default-name) --></pre>
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<p><strong>Notes:</strong></p>
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<ul><li>The <em>source-name</em> is the name of the embedded fragment, relative
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to the data source specified in the server configuration. The data source
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is searched in this order: <ol><li>Among the objects triggered. </li>
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<li>Among objects in the assembled directory within the repository of published
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objects maintained by the triggered cache manager function. These are objects
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that might have been fetched as a result of previous triggers and correspond
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to the assembled versions of fragments, intermediate results, and final publishable
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pages. <p>If the data source is a file system, the source-name is a file name.
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If the data source is HTTP, the source-name is the file name portion of a
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URL. </p>
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<p></p>
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</li>
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</ol>
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</li>
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<li>The <em>default-name</em> is the name of another fragment that might be
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used as a default when a specified fragment cannot be found. </li>
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<li>Nesting is supported. The triggered cache manager function uses the object
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dependency graph (ODG) specified in the server configuration to start the
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page assembler in the correct order to build pages. </li>
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</ul>
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<p>For example, when one fragment, <em>fragment A.html</em>, embeds another
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fragment, <em>fragment B.html</em>, it is said that <em>fragment A.html</em> is
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dependent on <em>fragment B.html</em>. This is denoted as either <em>B</em> --> <em>A</em> or
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as the ordered pair (<em>B</em>, <em>A</em>). It is said that there is a dependency
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relationship between <em>B</em> and <em>A</em>. Suppose that <em>A</em> also embeds
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another fragment, <em>fragment C.html</em>, and that <em>fragment C.html</em> in
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turn embeds <em>fragment D.html</em>. </p>
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<p>Suppose further that some other
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fragment, <em>fragment E.html</em>, also embeds <em>fragment C.html</em>. This
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relationship can be represented as a directed graph called the object dependency
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graph (ODG). The object dependency graph is for <em>fragment A.html</em> and <em>fragment
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C.html</em>. The HTML fragments that describe this look something like the
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following: </p>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><thead align="left"><tr><th valign="top" width="33.2089552238806%" id="d0e163"><em>Fragment A.html</em></th>
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<th valign="top" width="33.2089552238806%" id="d0e166"><em>Fragment C.html</em></th>
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<th valign="top" width="33.582089552238806%" id="d0e169"><em>Fragment E.html</em></th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" width="33.2089552238806%" headers="d0e163 "><pre><html>
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...
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<!-- %fragment(B.html) -->
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<!-- %fragment(C.html) -->
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...
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</html></pre>
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</td>
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<td valign="top" width="33.2089552238806%" headers="d0e166 "><pre><html>
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...
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<!-- %fragment(D.html) -->
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...
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</html></pre>
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</td>
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<td valign="top" width="33.582089552238806%" headers="d0e169 "><pre><html>
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...
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<!-- %fragment(C.html) -->
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...
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</html></pre>
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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<p>When the triggered cache manager function is instructed to publish <em>fragment
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C.html</em>, it determines that <em>C.html</em> embeds <em>D.html</em>. Similarly,
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when <em>A.html</em> and <em>E.html</em> are published, it determines <em>B</em> --> <em>A</em>, <em>C</em> --> <em>A</em>,
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and <em>C</em> --> <em>E</em>. These relationships are automatically entered into
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the object dependency graph when the fragments are processed by the publish
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trigger handler. If <em>D.html</em> is republished at a later time, the publish
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application can determine, by examining the ODG, that all of <em>C.html</em>, <em>A.html</em>,
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and <em>E.html</em> must be rebuilt but that the old copy of <em>B.html</em> can
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be used. Similarly, if only <em>B.html</em> changes, none of <em>C.html</em>, <em>D.html</em>,
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or <em>E.html</em> are affected. The entire process of discovering dependencies,
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updating the object dependency graph, and composing the correct and only the
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correct pages is all automatically performed by the publish trigger handler.
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</p>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><thead align="left"><tr><th valign="top" id="d0e252">Graphical representation of fragment <em>A.html</em></th>
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<th valign="top" id="d0e256">Graphical representation of fragment <em>E.html</em></th>
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<th valign="top" id="d0e260">Graphical representation of ODG for fragments <em>A.html</em> and <em>E.html</em>.</th>
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</tr>
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</thead>
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<tbody><tr><td align="center" valign="top" headers="d0e252 "><br /><img src="rzaie503.gif" alt="Graphical representation of fragment A.html." /><br /></td>
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<td align="center" valign="top" headers="d0e256 "><br /><img src="rzaie504.gif" alt="Graphical representation of fragment E.html." /><br /></td>
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<td align="center" valign="top" headers="d0e260 "><br /><img src="rzaie505.gif" alt="Graphical representation of ODG for fragments A.html and E.html." /><br /></td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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<div class="section"><h4 class="sectiontitle">Wrappers</h4><p>In some cases, most notably when HTML is
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generated automatically from HTML editors, it might be undesirable to use
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the full HTML content in a fragment. Such applications might insist on producing <html>
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and <body> tags, for example, which make the fragment nearly unusable.
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To manage this, fragments are also parsed for wrappers. </p>
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<p>A wrapper directive
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begins with the following tag: </p>
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<pre class="block"><!-- %begin-fragment( name ) --></pre>
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<p>A
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wrapper directive ends with the following tag: </p>
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<pre class="block"><!-- %end-fragment --></pre>
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<p>When
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these are encountered within a document, all text before the initial tag and
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following the final tag is discarded. Only the text between these tags is
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actually used during page composition. The selected text can be given a
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name other than the name of the file in which it occurs. This permits multiple
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fragments to exist in the same file. That is, if multiple <em>%begin-fragment</em> and <em>%end-fragment</em> tags
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are found, the file is treated as multiple files for the purpose of composing
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the page and managing the object dependency graph.</p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaieconcepts.htm" title="This topic provides concepts of functions on HTTP Server and IBM Web Administration for i5/OS interface.">Concepts of functions of HTTP Server</a></div>
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</div>
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</div>
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</body>
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</html>
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