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
REPAIR TABLE mdl_tablename - Click the Go button.
For example, to repair the Moodle log tables, type REPAIR TABLE mdl_log
In a similar manner to check the Moodle log table, type CHECK TABLE MDL_LOG. 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
- Forum discussion on a moodle database optimization script
- Performance Documentation on database repair and optimization
- Database Journal article on repairing database corruption in MySQL
