Joomla: Session is marked as crashed and should be repaired

"Error displaying the error page: Application Instantiation Error: Incorrect key file for table"
https://www.ostraining.com/blog/joomla/joomla-session-crashed/


The image below shows an error message that sometimes occurs on Joomla sites:

The message is actually fairly clear once you know what to look for.
The message says that one of your database tables has crashed. It says that the solution is repair that table.
Which table do we need to repair? The message above reads: Table './nass_j25testdb/usjbr_session
This contains two pieces of information:

• Our database name is nass_j25testdb
• Our database table is usjbr_session

That's the solution: we need to find the database called nass_j25testdb and repair the table called usjbr_session.

Repairing a database table

Login to your hosting account.
We need to find our "MySQL Databases". In this example, the link is marked below.

One very easy solution here is the "Modify Databases" option.

• Look for the Repair DB option.
• Choose the nass_j25testdb.
• Click the Repair DB button.

You'll now see a series of messages. One of those will probably say that your _session had a problem that has now been fixed:

Your site should now be back online.

An alternative solution

Here's another way to solve this problem.
Many hosting companies will give you direct access to the database via phpMyAdmin. You can see a sample link below:

Find your database on the left of the page:

Check the box next to your _session table.
Choose the Repair table option at the bottom of the page.

You'll get a message saying that your SQL query has been executed successfully. Your site should now be back online.