Moodle Structure Problems

WARNING: DO NOT ATTEMPT ANY OF THIS IF YOU DO NOT FULLY UNDERSTAND IT. YOU CAN DESTROY YOUR MOODLE SITE.

Recently I discovered our Moodle gradebook was playing up and not correctly recording marks from assignments as well as been unable to assign categories from quizes.

I tracked the problem down to the Moodle database losing all its default entries for its tables. The cause is unknown but is quite likely the UTF conversion utility I ran previously to make the system compatible with Asian languages for LOTE.

To fix this problem I needed to recreate the Moodle DB structure and then reimport the data.

Backup

First make a backup. I made a mistake the first time I tried repairing this and the backup I made saved me.

mysqldump -u backupacc -p -Q --opt moodle > moodleBackup.sql

I created a duplicate site with a clean DB (copy the moodle folder and create a new DB) and went through the install. This needs to have all your modules and blocks to ensure all tables are created.

I then dumped the structure from this new DB and the old DB and compared them using Meld (or any other diffing program will work).

 mysqldump -u backupacc -p --no-data --skip-add-drop-table moodletest2 > moodleGoodStruc.sql
mysqldump -u backupacc -p -d --skip-add-drop-table moodle > moodleOldStruc.sql

Using Meld determine if there are any extra tables or fields in your current system that don’t exist in the clean one.

Then you need to determine if it is safe to delete those tables / field in your main DB or if they need to be added to the clean system. e.g. grade_items_history.decimals and grade_items_history.display were in the main DB but not the new one. After searching for it discovered they can be removed (MDL-15985).

After getting them to match you need to dump your Moodle data from your main site.

You can speed up the next steps by reducing the size of backup_log if you wish. Just do a

Delete
FROM `mdl_backup_log`
WHERE `time` <1242777600

Where the time code is calculated as a unix time code from about a month before todays date. This can reduce alot of space of your DB, and improve import/export times.

mysqldump -u backupacc -p  --no-create-info --extended-insert --complete-insert moodle > moodleData200906171559.sql

You need the –complete-insert option to ensure each insert is labelled with field name, in case field order is different. I didn’t do this the first time and needed to restore the backup.

Testing Merge

Now you need to test it. Create a new empty DB and import the Structure then import your data.

mysql -u root -p moodleTest3 < moodleStruc.sql
mysql -u root -p moodleTest3 < moodleData200906171559.sql

Check that no errors occurred during import, this is when I discovered most of my problems with extra non existent field.

Prep for Applying

Put your site in Maintenance mode so no users can login while you are testing this. (i.e. when you restore data site will already be in maintenance mode)

When everything is OK do another backup, as after this you are going to delete it all. (I recommend taking your site completely offline for this, not just maintenance mode. Edit your config.php and temporarily change either the username, password or db name or your database settings.)

Now re-export the Data again (assuming your site has been running while you have been doing tests)

mysqldump -u backupacc -p  --no-create-info --extended-insert --complete-insert moodle > moodleData200906171559.sql

Applying to Site

WARNING: HAVE A GOOD RELIABLE BACKUP BEFORE THIS STEP.  THIS WILL DESTROY YOUR MOODLE SITE.

Now use phpMyAdmin to drop every table in the Moodle main DB. Just use Check All at the bottom and select Drop.

Now you need to redo your test restore above but to your main DB.

Once complete reconnect your config.php file and check everything on your site looks the same. Open some courses, check some gradebooks, have a look around.

When its OK take out of Maintenance mode and you should be good to go.

About James Rudd

Network Administrator at Sydney Boys High School
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