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SQL Server dual-computer Hot standby Technology

SQL Server dual-server hot backup can be achieved by publishing and subscribing, log shipping, and database mirroring.

Publish and subscribe

Publish and subscribe is to use SQL Server database replication technology to copy and distribute data or database objects from one database to another, and synchronize the data, so as to keep the source database and target database consistent. The replicated source data is configured by the publisher, the distributor is responsible for transferring the data obtained from the publisher to the subscriber, and the subscriber is responsible for receiving and maintaining the data. In practice, we should consider the application scenario and decide to use push subscription or pull subscription to achieve data synchronization.

Log delivery

In the SQLServer database engine, log shipping is used to continuously send transaction logs from one database (primary database) to another (secondary database). Continuously back up the transaction logs in the primary database, and then copy and restore them to the secondary database, which will keep the secondary database basically synchronized with the primary database. The target server acts as a backup server and can reassign query processing from the primary server to one or more read-only secondary servers. Log shipping can be used with databases that use the full or bulk-logged recovery model.

Database mirroring

Database mirroring is the main software solution to improve database availability. Mirroring is implemented on a per-database basis and applies only to databases that use the full recovery model. Database mirroring maintains two copies of a database that must reside on different SQL Server database engine instances (server instances). Typically, these server instances reside on computers in different locations. One server instance makes the database serve the client ("principal server"), while the other server instance acts as a hot or standby server ("mirror server"), depending on the configuration and state of the mirroring session. When synchronizing database mirroring sessions, database mirroring provides a hot standby server that supports rapid failover without data loss for committed transactions.

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