Transaction logs are helpful and important in the following scenarios-
- Individual transaction recovery
If an application issues a ROLLBACK statement, or if the Database Engine detects an error such as the loss of communication with a client, the log records are used to roll back the modifications made by an incomplete transaction.
- Recovery of all incomplete transactions when SQL Server is started
If a server that is running SQL Server fails, the databases may be left in a state where some modifications were never written from the buffer cache to the data files, and there may be some modifications from incomplete transactions in the data files. When an instance of SQL Server is started, it runs a recovery of each database. Every modification recorded in the log which may not have been written to the data files is rolled forward. Every incomplete transaction found in the transaction log is then rolled back to make sure the integrity of the database is preserved.
- Rolling a restored database, file, filegroup, or page forward to the point of failure
After a hardware loss or disk failure affecting the database files, you can restore the database to the point of failure.
- Supporting transactional replication
The Log Reader Agent monitors the transaction log of each database configured for transactional replication and copies the transactions marked for replication from the transaction log into the distribution database.
- Supporting high availability and disaster recovery solutions
The standby-server solutions, database mirroring, and
log shipping, rely heavily on the transaction log.