Symptoms

Confluence does not start up when using MySQL database. One of the following errors is displayed:

• Detected tables with non-default character encoding.
• Detected tables with non-default collation.

Cause

Confluence 5.2.4 added a check for tables with character encoding or collation setting that differs from the database default settings. Using non-default setting in a table can cause upgrade process to fail and leave the database in an inconsistent state. 

Resolution

Please see the How to Fix the Collation and Character Set of a MySQL Database manually knowledge base article and ensure that the database runs with unified character encoding and collation settings at all levels: database, table, and column.

From Confluence 7.3 and later, running on MySQL 5.7.9 or later, support to utf8mb4 was added. Make sure to select the appropriate encoding/collation to your system.