“The table ‘#__session’ is full” Error in Joomla

A client emailed us this Saturday morning and told us that he was seeing a blank page on every page on his website. Clearly that was the sign of a fatal error. Naturally, all we had to do was to search through the logs in order to find out what the problem is; it didn’t take us long to get to the bottom of it: the MySQL error log (located under the /var/lib/mysql folder) was inundated with the following error:

The table ‘#__session’ is full

Apparently, for some reason, the session table was reaching the maximum limit. That was weird. Typically, on dedicated servers (our client was hosting his website on a dedicated server), the limit of a MySQL table is only restricted by the amount of free hard disk space on the server. So we logged in to phpMyAdmin, and the first thing that we noticed was that the #__session table was using the MEMORY storage engine as described here, and that explained why the table was reaching a limit.

You see, MEMORY tables cannot exceed, in size, the value of the max heap table size global variable in MySQL, which defaults to 16 MB on a standard MySQL installation (if you wan to know the max heap table size on your specific MySQL instance, then do the following: 1) login to phpMyAdmin, 2) click on Variables on the top [without selecting any database], 3) in the Filters search box, enter the word “heap” and then press enter, 4) you will now be able to see what the value of the max heap table size is).

As you might have probably guessed, fixing this problem consisted of just increasing the value of the max heap table size, which we did the following way:

  • We ssh’d to the server.
  • We opened the file my.cnf located under the /etc folder (we always use vi for editing files in Linux).

  • We added the following line to it:


    (Note: You may already have the above line in your my.cnf file. In that case, all you need to do would be to increase the limit to a higher number.)

  • We restarted MySQL using the following command:

    /etc/init.d/mysql restart

    (Note: You can always restart MySQL from WHM in case you use it).

  • That fixed the problem.

Of course, we truncated the #__session table first, and we recommend that you truncate it in a cron job that runs every midnight, or else you may run into the same issue even after making the change above.

If your #__session table is getting full, and you are using the MEMORY storage engine, then try our solution above, it should work. If it doesn’t, or if you need help implementing it, then please contact us. Our rates are super affordable, our work is super professional, and we are super friendly!

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