This happens almost randomly on setup. So far encountered on Postgres, HSQL and Oracle, so it's not database-specific.

Can't seem to reliably reproduce it, which is annoying.

The workaround is to just restart Confluence, and continue with the setup as if it didn't happen.

Configuring the database failed. Couldnt create the database schema.
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'scheduler' defined in resource [/WEB-INF/schedulingSubsystemContext.xml] of ServletContext: Initialization of bean failed; nested exception is org.quartz.ObjectAlreadyExistsException: Unable to store Trigger with name: 'backupTrigger' and group: 'DEFAULT', because one already exists with this identification.
org.quartz.ObjectAlreadyExistsException: Unable to store Trigger with name: 'backupTrigger' and group: 'DEFAULT', because one already exists with this identification.
at org.quartz.simpl.RAMJobStore.storeTrigger(RAMJobStore.java:309)
at org.quartz.core.QuartzScheduler.scheduleJob(QuartzScheduler.java:608)
at org.quartz.impl.StdScheduler.scheduleJob(StdScheduler.java:231)
at org.springframework.scheduling.quartz.SchedulerFactoryBean.afterPropertiesSet(SchedulerFactoryBean.java:301)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:801)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:249)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:177)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:159)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:177)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:268)
at org.springframework.web.context.support.XmlWebApplicationContext.refresh(XmlWebApplicationContext.java:131)
at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:156)
at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:97)
at bucket.container.SpringContainerContext.refresh(SpringContainerContext.java:127)
at com.atlassian.confluence.setup.ConfluenceHibernateSetup.configureDatabase(ConfluenceHibernateSetup.java:102)
at com.atlassian.confluence.setup.ConfluenceHibernateSetup.configureDataSourceDatabase(ConfluenceHibernateSetup.java:70)
at com.atlassian.confluence.setup.actions.SetupDatasourceDatabaseAction.execute(SetupDatasourceDatabaseAction.java:62)