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Basic Database Administration

Unlike most web applications, SchoolTool does not use a relational database such as MySQL or PostgreSQL. Instead, it uses ZODB – the Zope Object Database. ZODB has some specific characteristics a SchoolTool site manager should be aware of.

Where is the data?

All the data in a given SchoolTool instance is stored in a file named Data.fs. On an Ubuntu system this file can be found in the /var/lib/schooltool/ directory. The additional files in that directory ending with .index, .lock, and .tmp are all used by the application in various ways, but they do not contain any data about your school which is not also included in the main Data.fs file.

Photos, reports, and other binary files are stored outside the Data.fs database in a blobs directory.

Automatic backups

Whenever SchoolTool is updated to a new version via Ubuntu’s update mechanisms, it creates a backup of the current database. It also compresses and retains previous backups. The most recent back up in /var/lib/schooltool/ has a .0 appended, like schooltool/Data.fs.0. Older backups are also gzipped, with increasing numbers as suffixes. schooltool/Data.fs.2.gz is older than schooltool/Data.fs.1.gz, for example.

How do I do a manual backup?

While it is possible to do a “hot” backup of SchoolTool’s database while the application is running, for the sake of simplicity this document will just cover an offline “cold” backup.

Basically, just stop the SchoolTool server, copy Data.fs and the blobs directory, and restart the server:

sudo /etc/init.d/schooltool stop
sudo cp /var/lib/schooltool/Data.fs /media/backups/schooltool/Data.fs-$(date +%Y%m%d-%H%M)
sudo cp -r /var/lib/schooltool/blobs /media/backups/schooltool/blobs-$(date +%Y%m%d-%H%M)
sudo /etc/init.d/schooltool start

Substitute the actual location of your backup in the place of /media/backups. The date +%Y%m%d-%H%M command embedded into the cp command is a bash command to embed the current date and time into the filename. That will allow you to keep a bunch of backups by date easily. Of course, if you’ve got a more sophisticated backup system than cp, by all means use that!

Restoring from a backup

In most cases, if you need to return to a previous automatic database backup, you should stop SchoolTool, rename the current Data.fs just in case you do need it later, remove the .0 from the most recent backup, and restart the server:

sudo /etc/init.d/schooltool stop
sudo mv /var/lib/schooltool/Data.fs /var/lib/schooltool/Data.fs.bad
sudo mv /var/lib/schooltool/Data.fs.0 /var/lib/schooltool/Data.fs
sudo /etc/init.d/schooltool start

If you need to try an even older backup, ungzip it:

sudo gunzip /var/lib/schooltool/Data.fs.1.gz

The procedure for restoring from a previous manual backup is the same, that is, copy the file to the Data.fs position, except only you know where it is coming from.

You will also need to backup and restore the files in the blobs directory using standard archiving tools (zip, tar, etc.).

What if My Database is Empty After an Upgrade?

If something goes awry during the backup process, it is possible that your current database will be moved into the first backup position (ending with .0), but a blank database will be in the “current” Data.fs position:

sudo mv /var/lib/schooltool/Data.fs.0 /var/lib/schooltool/Data.fs

How can I erase the entire database?

Delete the Data.fs file and the blobs directory. This is, of course, permanent. If there is the slightest chance you’ll ever want that data, moving rather than deleting the files is advisable.

Packing the database.

The ZODB is designed to keep a record of transactions, which can be used by an application to allow “undo” functionality. One implication of this, however, is that the database file grows in size as it stores a longer and longer list of changes to each object. To shrink the database back to a more efficient size, one can “pack” it.

Because SchoolTool does not allow you to undo transactions, you can pack the database at any time. It does not have to be done very frequently – certainly not daily. Packing the database monthly or weekly should suffice, but your mileage may vary. It may be something you do prior to high demand periods, such as before teachers submit grades. Backing up your database prior to packing it should not be necessary, but nonetheless it is not a bad idea.

To pack the database via the web, you must be logged in as “manager.” Navigate to the Server tab at the top of the page, then click on Actions: Pack Database:

_images/packing.png

Depending on your site’s database usage, this process could take several minutes and put a load on the server, so plan to pack the database at an off-peak time.