View source for How to check your database for corruption

Database corruption usually occurs as a result of a hardware (especially disk-based) failure, or when a disk becomes full. Typical symptoms are failure on login, with this message displayed:

 Session Replace: Table './moodle/mdl_sessions2' is marked as crashed and should be repaired

This problem mostly seems to affect MySQL.

==MySQL==

The problem can be repaired using the mysqlcheck command (the command you type is in bold and we assume the database name is 'moodle' and its type is MySQL):

 #'''mysqlcheck -u moodleuser -p --auto-repair moodle'''
 Enter password:
 moodle.adodb_logsql                      OK
 moodle.mdl_assignment                    OK
 moodle.mdl_assignment_submissions        OK
 ...
 moodle.mdl_log
 error    : Table './moodle/mdl_log' is marked as crashed and should be repaired
 ...
 moodle.mdl_sessions2
 error    : Table './moodle/mdl_sessions2' is marked as crashed and should be repaired
 
 Repairing tables
 moodle_18_latest.mdl_log                           OK
 moodle_18_latest.mdl_sessions2                     OK

Your mysql database server must be running when executing the mysqlcheck command. If there are problems with the tables, the auto-repair option will fix them as shown above. Note that the repair process can take a long time to complete. Re-run the command again to double-check that all is OK. 

Individual Moodle tables can be checked by using MySQL Admin/phpMyAdmin 

Individual Moodle tables may be repaired using MySQL Admin/PHPMyAdmin as follows:
# In the databases section, select the Moodle database.
# Click the SQL tab, then in the "Run SQL query/queries on database moodle" field type <code>REPAIR TABLE mdl_tablename</code>
# Click the Go button.
For example, to repair the Moodle log tables, type <code>REPAIR TABLE mdl_log</code>

In a similar manner to check the Moodle log table, type <code>CHECK TABLE MDL_LOG</code>.  This will either say OK or tell you what is wrong. For example it may say "Table marked as crashed".

==Other databases==

As I said above, this issue normally only occurs with MySQL.

==See also==

*[http://moodle.org/mod/forum/discuss.php?d=58208#279638 Forum discussion] on a moodle database optimization script
*[[Performance#MySQL_performance | Performance Documentation]] on database repair and optimization
*[http://www.databasejournal.com/features/mysql/article.php/10897_3300511_2 Database Journal article on repairing database corruption in MySQL]

[[Category:Administrator]]
[[de:Wie man die Konsistenz der Moodle-Datenbank prüft]]