Purpose of the Transaction Log

One very important component for performing proper backups and restores is the SQL Server transaction log. Every database has its own transaction log, which is implemented as one or more log files that reside on physical disk. The transaction log is used to record all transactions and the modifications that those transactions make to the database. The data in the log file is referred to as log records.

In general, the term transaction refers to a logical unit of work that can consist of queries and modifications to data. When referring to the transaction log, the term transaction refers specifically to data modifications only, for example, an UPDATE, INSERT, or DELETE operation, or a database schema change operation. ...

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