“Application Instantiation Error: Table ‘db.#__session’ doesn’t exist” Error in Joomla: 5 Possible Reasons

Note: You must replace #__ in the post below with your database alias which is the value of the variable $dbprefix that is defined in the configuration.php file of your Joomla website.

Another note: Always backup your Joomla database before making any modifications to it.

A not so uncommon fatal error on Joomla websites is the following error:

Application Instantiation Error: Table ‘db.#__session’ doesn’t exist

What the above error essentially means that Joomla is unable to read/write to the critical session table. This can be caused by one of the following (the below are listed in order of occurrences):

1. The session table is corrupted: The most common reason of the Table ‘db.#__session’ doesn’t exist error is corruption in the #__session table, this is especially the case when the table is using the MyISAM database storage engine (which is infamous for causing table corruption). If this is the case, then you should repair the table, which can be done by issuing the following query in phpMyAdmin:

   REPAIR TABLE `#__session`

   The above query should be sufficient to repair the table. If it doesn’t work, then you may need to reconstruct the table from scratch, which is described in the following section.

   Note: We recommend switching the database engine of the #__session table to InnoDB or to MEMORY as MyISAM is a very flimsy database engine.

2. The session table was deleted: One some occasions, the cause of the problem is a deleted #__session table. In this case, you will need to reconstruct the table. Reconstructing the table also works if the table is corrupted but cannot be repaired using the REPAIR syntax. Reconstruction of the #__session table is a safe process because the information in the #__session table is meant to be volatile and can be safely deleted at anytime.

   To reconstruct the table, you will need to run the following queries in phpMyAdmin (the following is compatible with Joomla 3.x):

   DROP TABLE `#__session`;
   CREATE TABLE IF NOT EXISTS `#__session` (
     `session_id` varchar(191) NOT NULL DEFAULT '',
     `client_id` tinyint(3) unsigned NOT NULL DEFAULT 0,
     `guest` tinyint(4) unsigned DEFAULT 1,
     `time` varchar(14) DEFAULT '',
     `data` mediumtext,
     `userid` int(11) DEFAULT 0,
     `username` varchar(150) DEFAULT '',
     PRIMARY KEY (`session_id`),
     KEY `userid` (`userid`),
     KEY `time` (`time`)
   ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE=utf8mb4_unicode_ci;

   The above code should drop your #__session table and then reconstruct it.

3. The database user doesn’t have full read/write control over the session table: A not so uncommon cause of the problem is a user which doesn’t have full privileges over the #__session table. This is likely to happen when the Joomla database is managed at a granular level, and not through a mainstream system (like WHM). Fixing the problem is usually done by granting full read/write permissions on the #__session table (this is typically done by a system administrator).

4. The database is empty: Last week, we had the Table ‘db.#__session’ doesn’t exist problem on a website, and it turned out that the database was empty. It didn’t have a single table, not one. The database did exist and the connection parameters were correct, but it was empty (if the database didn’t exist, or if we had the wrong database credentials in the configuration.php file, then we would have seen the Application Instantiation Error fatal error instead). We fixed this problem by reverting to an old backup. The backup didn’t contain the most up-to-date data, but it was much better than nothing.

5. The configuration file is pointing to a different database: On some instances, we have seen a configuration.php file where the database parameters are pointing to an existing database, but not to the Joomla database. This is not common but it can happen, and it is usually caused by a human error: for example, the system administrator copied the content of the Joomla database to another database, emptied the original database (and used it for a different purpose), but did not update the parameters in the configuration.php file to point to the new database. Fixing the problem simply consists of updating the database parameters in the configuration.php file to point to the actual database.

We hope that you found our post useful and that it helped you solve your problem. If it didn’t, then you can always contact us. We are always happy to serve, our prices are super cheap, and we really love to have you as a client and a friend!