Checkpoints flush dirty data pages from the buffer cache of the current database to disk. This minimizes the active portion of the log that must be processed during a full recovery of a database. During a full recovery, the following types of actions are performed:
- The log records of modifications not flushed to disk before the system stopped are rolled forward.
- All modifications associated with incomplete transactions, such as transactions for which there is no COMMIT or ROLLBACK log record, are rolled back.
Checkpoints occur in the following situations:
- A CHECKPOINT statement is explicitly executed. A checkpoint occurs in the current database for the connection.
- A minimally logged operation is performed in the database; for example, a bulk-copy operation is performed on a database that is using the Bulk-Logged recovery model.
- Database files have been added or removed by using ALTER DATABASE.
- An instance of SQL Server is stopped by a SHUTDOWN statement or by stopping the SQL Server (MSSQLSERVER) service. Either action causes a checkpoint in each database in the instance of SQL Server.
- An instance of SQL Server periodically generates automatic checkpoints in each database to reduce the time that the instance would take to recover the database.
- A database backup is taken.
- An activity requiring a database shutdown is performed. For example, AUTO_CLOSE is ON and the last user connection to the database is closed, or a database option change is made that requires a restart of the database.
