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1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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2 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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3 <html xmlns="http://www.w3.org/1999/xhtml">
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4 <head>
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5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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6 <title>digilib -- Digital Image Library</title>
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7 </head>
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8 <body>
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9 <table border="0" cellspacing="0" cellpadding="10">
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10 <tr>
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11 <td bgcolor="#a0a0a0"> </td>
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12 <td>
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13 <img src="images/digilib-logo-big.png" align="left" />
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14 <h1>
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15 <tt>digilib</tt> -- a versatile image viewing environment for the internet
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16 </h1>
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17 </td>
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18 </tr>
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19 <tr>
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20 <td bgcolor="#a0a0a0" valign="top" align="right">
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21 <p>
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22 <b><a href="index.html">Info</a> </b>
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23 </p>
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24 <p>
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25 <b><a href="http://developer.berlios.de/projects/digilib/">Project</a> </b>
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26 </p>
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27 <p>
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28 <b><a href="http://developer.berlios.de/project/showfiles.php?group_id=251">Download</a>
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29 </b>
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30 </p>
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31 <p>
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32 <b><a href="docs.html">Docs</a></b>
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33 <br />
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34 <a href="build-maven.html">Building</a>
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35 <br />
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36 <a href="digilib-config.html">Configuring</a>
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37 <br />
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38 <a href="http://developer.berlios.de/docman/?group_id=251">...more</a>
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39 </p>
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40 <p>
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41 <b><a href="tips.html">Tips</a> </b>
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42 </p>
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43 <p>
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44 <b><a href="http://hg.berlios.de/repos/digilib">Source</a> </b>
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45 </p>
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46 </td>
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47 <td>
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48
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49
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50 <p>Some tips for running digilib</p>
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51 <ul>
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52 <li>
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53 <a href="#vm_settings">Java VM settings for digilib</a>
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54 </li>
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55 <li>
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56 <a href="#prescaled_images">Prescaled images</a>
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57 </li>
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58 <li>
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59 <a href="#installing_jai">Installing JAI</a>
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60 </li>
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61 </ul>
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62
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63 <h1 id="vm_settings">Java VM settings for digilib</h1>
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64
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65 <p>The Java virtual machine (Java-VM) only uses a fixed amount of memory for
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66 its operations. When an operation needs more memory than available it aborts
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67 with an error ("out of memory error").</p>
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68 <p>digilib can need a lot of memory depending on the size and type of images.
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69 Since digilib runs as a servlet under Tomcat its in the same VM as the Tomcat
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70 server.</p>
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71 <p>The amount of memory Tomcat (version 5.0) uses is configured by creating a
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72 "setenv.sh" script with a line</p>
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73 <pre> CATALINA_OPTS="-Xmx512m"
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74 </pre>
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75 <p>in Tomcat's "bin" directory (giving 512MB in this case).</p>
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76 <p>
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77 You can check the amount of memory your digilib instance has available on the
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78 bottom of the web page /server/dlConfig.jsp in your digilib instance (e.g. <a
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79 href="http://digilib.mpiwg-berlin.mpg.de/digitallibrary/server/dlConfig.jsp"
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80 class="external free" rel="nofollow">http://digilib.mpiwg-berlin.mpg.de/digitallibrary/server/dlConfig.jsp</a>).
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81 </p>
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82
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83 <h1 id="prescaled_images">Prescaled images</h1>
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84
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85 <p>You can provide any number of scaled-down versions of your images that
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86 digilib uses when a smaller version of an image is requested. Since less data
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87 has to be read and processed this can speed up digilib's performance quite a
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88 lot.</p>
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89 <p>The actual process is that the client requests a certain target size,
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90 digilib scans all available scaled-down versions of the same image, selects the
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91 smallest image that is larger than the requested size and scales it down to the
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92 requested size.</p>
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93 <p>The scaled-down versions of the image have to have the same file name as
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94 the original hi-res file. They can have a different type and extension (e.g.
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95 img002.jpg for img002.TIFF)</p>
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96 <p>The scaled down images have to be in the same subdirectory (the part that
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97 shows up in digilib's "fn" parameter) as the hi-res file. The first part of each
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98 directory tree is configured by the basedir-list parameter in
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99 digilib-config.xml.</p>
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100 <p>The sequence of directories in basedir-list is from hi-res to lo-res.
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101 Images must be present in the hires directory but they need not be present in
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102 all lower-res directories.</p>
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103 <p>e.g. if digilib-config.xml contains</p>
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104 <pre> <parameter name="basedir-list" value="/images:/scaled:/thumb" />
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105 </pre>
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106 <p>and a user requests the image "books/book1/page0002" digilib looks for</p>
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107 <pre> /thumb/books/book1/page0002.*
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108 /scaled/books/book1/page002.*
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109 /images/books/book1/page002.*
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110 </pre>
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111 <p>and uses the first image that is bigger than or equal to the requested
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112 size.</p>
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113 <p>
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114 For batch-prescaling our images we use a script called "scale-o-mat" that uses a
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115 lot of freely available imaging libraries (ImageMagick, libtiff, netpbm) and is
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116 available in our public CVS <a
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117 href="http://itgroup.mpiwg-berlin.mpg.de/cgi-bin/cvsweb.cgi/scaleomat/"
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118 class="external autonumber" rel="nofollow">[1]</a>. The script is given a
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119 hi-res base directory, a destination base directory, a destination size and a
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120 starting directory. It then processes all files in the starting directory and
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121 all its subdirectories and creates scaled images in corresponding directories
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122 under the destination base directory.
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123 </p>
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124 <p>We currently use prescaled thumbnails of 100 pixels and images for browser
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125 display of 1500 pixels. Remember that the prescaled image has to be larger (or
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126 the same size) than the requested image size!</p>
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127 <p>There is another optimization in digilib: if the requested image is exactly
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128 the same size and type as the prescaled image then the prescaled image is sent
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129 unmodified to the client which is a lot faster. So it makes sense to produce
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130 thumbnails of exactly 90 pixels width when they are used in an HTML page where
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131 all images are 90 pixels wide.</p>
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132
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133
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134 <h1 id="installing_jai">Installing JAI</h1>
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135
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136 <p>
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137 In theory you can install the <a
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138 href="http://java.sun.com/javase/technologies/desktop/media/jai/"
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139 class="external text" rel="nofollow">Java Advanced Imaging</a> and JAI-ImageIO
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140 JAR files <code>jai_core.jar, jai_codec.jar, jai_imageio.jar</code> (and native
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141 library files if available) in the <code>/WEB-INF/lib/</code> directory of the
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142 digilib web application.
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143 </p>
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144 <p>But there are classloader issues. Newer versions of Tomcat refuse to load
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145 the libraries and I found that in some cases digilib stopped reading TIFF files
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146 after a period of running.</p>
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147 <p>
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148 In these cases it helped to install the JAI files in Tomcats <code>lib/</code>
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149 directory or Jettys <code>lib/ext/</code> or globally in the local Java JDK
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150 installation (i.e. in the Java's /jre/lib/ext/ directory on linux).
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151 </p>
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152
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153
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154 <h1 id="mpiwg_setup">Sample setup</h1>
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155
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156 <p>The current digilib setup at the MPIWG (as of December 2010):</p>
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157 <ul>
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158 <li>
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159 One frontend server running the lightweight web-multiplexer <a
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160 href="http://www.apsis.ch/pound/" class="external text" rel="nofollow">pound</a>
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161 on port 80 that distributes requests to three servers runnning digilib
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162 </li>
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163 <li>
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164 the three servers run digilib under <a
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165 href="http://www.eclipse.org/jetty/" class="external text"
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166 rel="nofollow">Jetty</a> on port 8080 without Apache
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167 <ul>
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168 <li>one server is the frontend server (Linux 32bit, Dual
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169 2.4GHz Xeon, 2GB RAM)</li>
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170 <li>the other server is a separate, newer machine (Linux 64bit, Dual 1.8GHz
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171 Opteron, 2GB RAM)</li>
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172 <li>the third server is a separate, newer machine (Linux 32bit, Dual 2.8GHz
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173 Xeon, 4GB RAM)</li>
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174 </ul>
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175 </li>
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176 <li>
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177 the digilib instances (digilib 2.0b1 as of 12.12.2011) run on Jetty 8.0.4 on Java
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178 1.6.0_26 with 1GB of <a href="#vm_settings">Java VM memory
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179 for digilib</a> (-Xmx1024m) with JAI (1.1.3) and JAI-ImageIO (1.1) <a
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180 href="#installing_jai">installed in the Jetty/lib/ext</a>(!)
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181 </li>
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182 <li>both digilib servers access all image files over NFS (over GBit
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183 Ethernet) from a central file server (Solaris 10, Sun Fire 240, multiple RAIDs
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184 on Fibrechannel)</li>
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185 </ul>
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186
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187 </td>
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188 </tr>
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189 <tr>
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190 <td style="padding: 0px" align="left">
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191 <a href="http://developer.berlios.de"> <img
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192 src="http://developer.berlios.de/bslogo.php?group_id=0&type=1" width="124"
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193 height="32" border="0" alt="BerliOS Logo" />
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194 </a>
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195 </td>
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196 <td></td>
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197 </tr>
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198 </table>
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199
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200 </body>
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201 </html> |
