A multi-tenant setup (a.k.a "virtual mode", "multi-wiki" or "farm mode") allows you to have several wikis running on the same XWiki instance (i.e. in the same JVM).

Each wiki has its own database schema, thus allowing for a complete data separation between the different wikis in the same instance.

The main advantage of multi-tenancy is performance optimization. A single XWiki instance on a physical machine (thus a single Servlet Container) will perform much better than having several XWiki instances running on the same machine, which wouldn't scale. As an example known XWiki multi-tenant instances hosts several thousands hundreds to several thousands wikis on a single XWiki instance.

Requirements

The multi-tenancy feature currently works only on some databases:

• Databases known to work are: MySQL and Oracle. 
• PostgreSQL is currently not supported as the JDBC driver doesn't support setCatalog() for changing databases as PostgreSQL connections are pointed to a specific database at connection time. see jira issue XWIKI-1960.
• HSQLDB and Derby are currently not supported either

In addition to having a supported database you'll also need:

• Choose one instance of XWiki that has been installed on your network. The database name for this wiki should be xwiki. If you've still got to install the XWiki instance, please refer to the installation guide and install a XWiki Enterprise first.
• Admin privileges on this XWiki instance
• You need to be sure that the xwiki user used to the create the main database has the correct permissions to be able to create other schemas since each subwiki will create a new database schema.
• Able to restart the java container (e.g. Tomcat or Jetty), or can have this restarted on demand.
  • The xwiki.cfg file will also have to be modified, so you will need to have write access to this file on the server.

Set up

• Stop your XWiki instance, edit the WEB-INF/xwiki.cfg file, look for the xwiki.virtual property and set it to 1: xwiki.virtual=1. Restart your XWiki instance.
• Install the Wiki Manager Application Extension. 

Starting with XWiki Enterprise 3.3 you can easily install the Wiki Manager Application using the Extension Manager by following these steps:

• Go the Administration page, find the "Extension Manager" section and click on "Add Extension"
• Click on "Advanced Install", enter the following information and then click the "Install" button and then the "Apply" button to confirm the installation
  • extension id: org.xwiki.platform:xwiki-platform-wiki-manager-ui
  • extension version: 3.3 (adapt to use the version you wish to install, make it match the version of XWiki Enterprise you're using)
• Verify that the Wiki Manager extension is correctly installed by navigating to the WikiManager.WebHome page which should now exist.

You now have a multi-tenant installation and can proceed to use the Wiki Manager Application to create subwikis.