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  28  <H2><A NAME="5_1">5.1 Enabling the cache system</A></H2>
  29  <P> The enabling disabling of the cache system is controlled by two
  30   defines (in jpg-config.php)</P>
  31  <P><DIV class="phpscript"><CODE><FONT color="#000000"> <FONT color="#0000BB">
  32  &nbsp;DEFINE</FONT><FONT color="#007700">(</FONT><FONT color="#DD0000">
  33  &quot;USE_CACHE&quot;</FONT><FONT color="#007700">,</FONT><FONT color="#0000BB">
  34  true</FONT><FONT color="#007700">);
  35  <BR></FONT><FONT color="#0000BB">DEFINE</FONT><FONT color="#007700">(</FONT><FONT
  36  color="#DD0000">&quot;READ_CACHE&quot;</FONT><FONT color="#007700">,</FONT><FONT color="#0000BB">
  37  true</FONT><FONT color="#007700">)</FONT><FONT color="#0000BB"></FONT></FONT>
  38  </CODE></DIV></P>
  39  <P></P>
  40  <P> The first of these, USE_CACHE, is the master-switch which must be
  41   set to true to enable the caching system. The second switch READ_CACHE
  42   very seldom needs to be changed.</P>
  43  <P> This second switch basically tells whether or not JpGraph should
  44   ever look in the cache. Setting this to false and the master-switch to
  45   true would then always generate an new updated image file in the cache
  46   and this new image would be send back to the browser. The main use for
  47   this (admittedly) strange setting is if you like to have the side
  48   effect of the script that a fresh image is always stored in the cache
  49   directory.</P>
  50  <P> Once you have enabled the cache you must also make sure that a valid
  51   cache directory is setup. The cache directory is specified with the
  52   define</P>
  53  <P><DIV class="phpscript"><CODE><FONT color="#000000"> <FONT color="#0000BB">
  54  &nbsp;DEFINE</FONT><FONT color="#007700">(</FONT><FONT color="#DD0000">
  55  &quot;CACHE_DIR&quot;</FONT><FONT color="#007700">,</FONT><FONT color="#DD0000">
  56  &quot;/tmp/jpgraph_cache/&quot;</FONT><FONT color="#007700">);</FONT><FONT color="#0000BB">
  57  </FONT></FONT></CODE></DIV></P>
  58  <P></P>
  59  <P> You can of course change the default directory to whatever directory
  60   you fancy. But, you must remember one important thing.<STRONG> The
  61   cache directory must be writable for the user running Apache/PHP</STRONG>
  62  .</P>
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