New Active geo-replication optimization is coming to production soon in Azure SQL DB
Published date: June 26, 2019
To ensure reliable data replication to the secondary databases, SQL database engineers have implemented a set of optimizations designed for the configurations where the secondary database has lower compute size (lower SLO) than the primary. These configurations are not recommended and have been causing outages of the secondary database due to its compute capacity being insufficient to keep up with the primary database's rate of change. A secondary database that is lagging behind the primary also risks a large data loss should a forced failover be required. To mitigate these risks, effective July 1st active geo-replication will start periodically throttling the primaries to allow their secondaries to catch up. To ensure that your application's performance is not impacted by throttling, we strongly recommend increasing the compute size of the secondary database. For detailed guidance on configuring the seconday database, see Configuring secondary database.