US Patent 11144407 Synchronous database geo-mirroring using delayed visibility write operations

Systems and methods are disclosed to implement a synchronous database mirroring technique using delayed visibility write operations. In embodiments, a durable log of write operations in a primary database is replicated to a secondary database. The two databases do not make corresponding operations durable in a synchronous manner. However, the two databases coordinate to provide a visible view of the two durable logs that is guaranteed be durable in both databases. In embodiments, the primary database may monitor the state of the durable log of the secondary database, and periodically update the visible range of the logs to include operations that have been made durable in both databases. Advantageously, the visible range of the logs is permitted to grow asynchronously from the logs themselves, so that the two databases can provide a synchronized visible view of the log data without placing timing constrains on the data's durability.