Confluence does not support Postgres 9.6, and will throw error messages like the following:
Upgrading the Postgres Driver to the newest version seems to resolve the problem, however Atlassian Support will not be able to provide support for this configuration until this improvement is implemented in a future version.
- Shut down Confluence
- Copy confluence-install/confluence/WEB-INF/lib/postgresql-9.x-xxxx.jdbc4.jar to a safe location as a backup, and then delete the file.
- From the Postgres Website, download the most recent driver and copy it to the same location
- Despite its name, the JDBC 9.4 driver is compatible with Postgres 9.6
- Start Confluence again
This is documented here