Compatibility Considerations

MyISAM storage engine

MyISAM (the default storage engine for MySQL) does not support transactions. If there is an error while data is being saved to the database, XWiki will attempt to rollback the transaction to its previous known good state. If you use MyISAM it will do nothing, leaving the database in whatever state it was in when the error occurred.

If you use MySQL with default engine MyISAM, you will most likely corrupt your database. We highly recommend using a storage engine such as InnoDB which supports transactions.

MySQL versions older than 5.0

XWiki does not fully work with MySQL versions 4.x or lower, due to several limitations of the way the SQL standards are implemented in MySQL, limited support for non-latin1 encodings, the flaky integration of Hibernate and MySQL 4, and other things. Most of the application works fine, but there are some parts that cannot be easily fixed, so if you must use MySQL 4.x, you're doing it on your own. Seriously, MySQL 4 is pretty old and buggy, you should consider upgrading.

Installation Steps

Follow these instructions:

  • Download and install MySQL 5.X or greater.
  • Start the MySQL server. You can do that in several ways. For example:
    mysqld --console
  • Create the wiki database. You can use the name you want for the database, but you will have to set hibernate configuration file and xwiki.cfg file accordingly. You can create the database in several ways. For example:
    mysql -u root -e "create database xwiki default character set utf8"
  • Give all privileges to the xwiki user for accessing the xwiki database. You can do that in several ways. For example (if you get connection problems try localhost instead of the IP address below):
    mysql -u root -e "grant all privileges on xwiki.* to xwiki@localhost identified by 'xwiki'"
  • Please make sure that the DNS-name "localhost" is defined in your hosts-file (i.e. /etc/hosts)
  • You need to have the MySQL JDBC Driver JAR (named mysql-connector-java*.jar) installed in XWiki's WAR file. If this file isn't present in XWiki's WEB-INF/lib directory you'll need to download it and copy it there. You can download it from the MySQL Connector/J Driver page or directly from the Maven Central Repository.

    You need the 5.x version or higher. The 3.x version doesn't handle Boolean data correctly and will either throw errors, or will make all documents hidden by default.

  • Now you need to tell XWiki to use MySQL. To do this, edit the WEB-INF/hibernate.cfg.xml file where you have expanded the XWiki WAR file and replace the matching properties with the following ones:
    <property name="connection.url">jdbc:mysql://localhost/xwiki</property>
    <property name="connection.username">xwiki</property>
    <property name="connection.password">xwiki</property>
    <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

By default MySQL only accepts packets that are smaller than 1MB. If you get the "Packet for query is too large (max_allowed_packet)" error then see the Packet too large error page. For example to increase the packet size to 32M you could start the MySQL server with:

mysqld --console --max_allowed_packet=32M

If an empty Xwiki starts with no errors, but you unable to upload the default set of pages (XAR file) also try to increase *max_allowed_packet* parameter as shown above.   
XWiki does not create the Database Indexes automatically. You can use the Admin Tools Application for that or create them manually

Troubleshooting

Unable to login to MySQL Console

When running 

mysql -u root -e "create database xwiki default character set utf8

you may get a

ERROR 1045 (28000): Access denied for user 'xwiki'@'localhost' (using password: YES)

This means that you have a password set for the MySQL root user, but you are not specifying it in the console command. You must also use the -p parameter. Using this you will be prompted to enter the password and be allowed to login to the MySQL console and create the database.

Can't create test file

When running mysqld --console you may get the following (especially if you're on a Mac):

071111 17:20:53 [Warning] Can't create test file /usr/local/mysql-5.0.45-osx10.4-i686/data/Vincent.lower-test
071111 17:20:53 [Warning] Can't create test file /usr/local/mysql-5.0.45-osx10.4-i686/data/Vincent.lower-test
mysqld: Can't change dir to '/usr/local/mysql-5.0.45-osx10.4-i686/data/' (Errcode: 13)
071111 17:20:53 [ERROR] Aborting

To start MySQL run the following instead:

sudo /usr/local/mysql/bin/mysqld_safe --user=mysql

Data Truncation Error

If you receive an Exception like the following while installing/upgrading XWiki, chances are that you are using an outdated version of MySQLConnectorJ.

Caused by: java.sql.BatchUpdateException: Data truncation: Out of
range value adjusted for column 'XWD_HIDDEN' at row 1
      at com.mysql.jdbc.PreparedStatement.executeBatch(PreparedStatement.java:894)
      at org.apache.commons.dbcp.DelegatingStatement.executeBatch(DelegatingStatement.java:294)
      at org.apache.commons.dbcp.DelegatingStatement.executeBatch(DelegatingStatement.java:294)
      at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:48)
      at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:246)

On Linux, mysql-connector-java-3.x has proven not to work due to a bug in the handling of UTF-8 and lack of support for Boolean types.

Upgrading to the latest version of MySQLConnectorJ should solve such an error in most of the cases.

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