<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Chapter 9. Using the JpGraph cache system</title><link rel="stylesheet" type="text/css" href="manual.css"><meta name="generator" content="DocBook XSL Stylesheets V1.76.0"><link rel="home" href="index.html" title="JpGraph Manual"><link rel="up" href="pt02.html" title="Part II. Basic graph creation"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 9. Using the JpGraph cache system</th></tr><tr><td width="20%" align="left"> </td><th width="60%" align="center">Part II. Basic graph creation</th><td width="20%" align="right"> </td></tr></table><hr></div><div class="chapter" title="Chapter 9. Using the JpGraph cache system"><div class="titlepage"><div><div><h2 class="title"><a name="chap.using-cache"></a>Chapter 9. Using the JpGraph cache system</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ch09.html#id2500903">9.1. Enabling the library cache system</a></span></dt><dt><span class="sect1"><a href="ch09s02.html">9.2. Permission settings for the cache files</a></span></dt><dt><span class="sect1"><a href="ch09s03.html">9.3. Using the cache in your script</a></span></dt><dd><dl><dt><span class="sect2"><a href="ch09s03.html#id2535216">9.3.1. Manually controlling the cached image</a></span></dt></dl></dd><dt><span class="sect1"><a href="ch09s04.html">9.4. Using the cache with Client Side Image Maps (CSIM)</a></span></dt></dl></div>
<p>To reduce load on the web server JpGraph implements an advanced caching system which
avoids the burden of always having to run the full image script. The library supports
two primary ways of significantly increase performance, using the built in cache system
described in this section and the use of a PHP accelerator described in <a class="xref" href="ch11.html" title="Chapter 11. NuSphere PHP accelerator">Chapter 11. <i>NuSphere PHP accelerator</i></a></p>
<p>Depending on the complexity of the image script, for example if it is doing several DB
lookups, the use of the library cache system (which will avoid running the graph scripts
completely if possible) can make a for very drastic performance increase.</p>
<p><a class="xref" href="ch09.html#fig.cache-overview" title="Figure 9.1. Library cache principle">Figure 9.1. Library cache principle</a>shows an overview of the cache system in the library.</p>
<p>
</p><div class="figure"><a name="fig.cache-overview"></a><p class="title"><b>Figure 9.1. Library cache principle</b></p><div class="figure-contents">
<div class="mediaobject"><img src="images/cache_principles.png" alt="Library cache principle"></div>
</div></div><p><br class="figure-break">
</p>
<p>The rationale behind this is the observation that very few graphs are really
real-time, i.e. needs to be updated absolutely every time the graphing script is called.
For many graphs in a WEB-environment one can often get good precision by restricting the
graphs to only be updated, say, a few times each day. Of course, if truly live data is
what is needed then the cache system can not be used since then, by the nature of live
data, the graph script must be called at each instance to get the latest available data,
most probably from a database.</p>
<div class="sect1" title="Enabling the library cache system"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2500903"></a>Enabling the library cache system</h2></div></div></div>
<p>The enabling and disabling of the cache system is controlled by three defines in
<code class="filename">jpg-config.php</code></p>
<p>
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<p><code class="code">DEFINE("USE_CACHE",true)</code></p>
</li><li class="listitem">
<p><code class="code">DEFINE("READ_CACHE",true)</code></p>
</li><li class="listitem">
<p><code class="code">DEFINE("CACHE_DIR","/tmp/jpgraph_cache/")</code></p>
</li></ol></div><p>
</p>
<p>The first of these, <code class="code">USE_CACHE</code>, is the master-switch which must be set
to true to enable the caching system. </p>
<p>The second switch, <code class="code">READ_CACHE</code> very seldom needs to be changed. This
second switch basically tells whether or not JpGraph should ever look in the cache.
Setting this to false and the master-switch to true would then always generate a new
updated image file in the cache and this new image would be send back to the
browser. The main use for this (admittedly) strange setting is if you like to have
the side effect of the script that a fresh image is always stored in the cache
directory. </p>
<p>The third define is not really a switch but a directory specification that tells
the library what directory to use as the cache directory (where the cached images
are stored). </p>
<p>The cache directory (<code class="code">CACHE_DIR</code>) can be set to an arbitrary directory
but the important thing to keep in mind is that the cache directory must be read and
writable for the process running PHP. </p>
<p>
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
<p>The directory name given should be an absolute directory path and <span class="bold"><strong>not</strong></span> a file path relative to the document
root.</p>
</div><p>
</p>
</div>
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