Problem

After upgrading MySQL, Confluence may not start up and the following warning will appear in the atlassian-confluence.log:

2020-03-03 08:58:36,338 WARN [C3P0PooledConnectionPoolManager[identityToken->2zpby9a818mmioianzgpk|2f53fb9]-HelperThread-#2] [mchange.v2.resourcepool.BasicResourcePool] log com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@57c970a0 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 
java.sql.SQLException: Unknown system variable 'tx_isolation'

Environment

Any Confluence version using a MySQL database

Cause

Due to licensing constraints, we are not able to bundle MySQL or Oracle database drivers with Confluence, so you will need to manually download and install the latest MySQL driver before you start Confluence. If this step is not taken Confluence may fail to start up.

Solution

Download and install the latest MySQL driver. 

MySQL 5.6 and 5.7

1. Stop Confluence.
2. Head to Database JDBC Drivers and download the appropriate driver. The driver file will be called something like mysql-connector-java-5.1.xx-bin.jar
3. Drop the .jar file in your <installation-directory>/confluence/WEB-INF/lib directory.
4. Restart Confluence then go to http://localhost:<port> in your browser to continue the setup process.

MySQL 8.0

1. Stop Confluence.
2. Head to Database JDBC Drivers and download the appropriate driver for MySQL 8. The driver file will be called something like mysql-connector-java-8.0.xx-bin.jar
3. Drop the .jar file in your <installation-directory>/confluence/WEB-INF/lib directory.
4. Restart Confluence then go to http://localhost:<port> in your browser to continue the setup process.