source: trunk/language/en_UK/help/maintenance.html @ 4484

<h2>Maintenance</h2>

<p>To optimize page generation time, Piwigo uses cached
information. For example, instead of counting the number of pictures
contained in each category at each page reload, this information is stored
in the database. In theory, this information should always be correct, but
sometimes an error can occur and cached information becomes wrong.</p>

<p>Some informations become useless with time. Deleting this useless
information from database make you save disk space.</p>

<ul>

  <li><strong>Update categories informations:</strong> For each category,
  informations to update or control are the following : list of parent
  categories, number of pictures, date of the last picture, position among
  brother categories, position among all categories. This action also checks
  the coherence of representative picture.</li>

  <li><strong>Update images informations:</strong> For each picture,
  informations to update are : full path to file, average
  rate. <em>Warning</em>: do not get confuse with metadata informations
  which can be synchronized from <span class="pwgScreen">Administration,
  Categories, Synchronize</span> or by reaching the modification screen of a
  single picture (through <span class="pwgScreen">Picture</span> for
  example).</li>

  <li><strong>Repair and optimize database:</strong>
  For each table, re-odrer, repair and optimize operations are done.
  </li>
</ul>

<ul>
  <li><strong>Purge history detail:</strong> Delete all lines from
  <code>history</code> table. Screen <span class="pwgScreen">Administration,
  Specials, History</span> shows no informations anymore on past
  history. <em>Warning</em>: all data will be lost and there is no way to
  get informations back.</li>

  <li><strong>Purge history summary:</strong> Delete all the summary information about visit history. This summary is calculated from the history detail.</li>

  <li><strong>Purge sessions:</strong> Delete expired user sessions.</li>

  <li><strong>Purge never used notification feeds</strong></li>

  <li><strong>Purge search history</strong></li>
  
  <li><strong>Purge compiled templates</strong></li>  
</ul>