Promoting a read replica can serve several different purposes, such as allowing you to apply time-consuming schema changes without disrupting your primary instance, or to split your database into shards by partitioning data onto multiple primary instances.

The read replica reboots when you promote it and the promotion can take a while since there are significant changes that have to be made to the database configuration to disconnect it as a replica and bring it up as a primary. Configuration items such as backup retention and parameter groups are copied from the original primary to the newly promoted primary.

Transactions to the read replica must be stopped before promotion, and the database must be in a read-only state.