Checkpoint

For performance reasons, the Database Engine performs modifications to database pages in memory—in the buffer cache—and does not write these pages to disk after every change. Rather, the Database Engine periodically issues a checkpoint on each database. A checkpoint writes the current in-memory modified pages (known as dirty pages) and transaction log information from memory to disk and, also, records information about the transaction log.

The Database Engine supports several types of checkpoints: automatic, indirect, manual, and internal. The following table summarizes the types of checkpoints


Automatic: EXEC sp_configure 'recovery interval','seconds'
Description: Issued automatically in the background to meet the upper time limit suggested by the recovery interval server configuration option. Automatic checkpoints run to completion. Automatic checkpoints are throttled based on the number of outstanding writes and whether the Database Engine detects an increase in write latency above 20 milliseconds.


Indirect: ALTER DATABASE … SET TARGET_RECOVERY_TIME =target_recovery_time{ SECONDS | MINUTES }
Description: Issued in the background to meet a user-specified target recovery time for a given database. The default target recovery time is 0, which causes automatic checkpoint heuristics to be used on the database. If you have used ALTER DATABASE to set TARGET_RECOVERY_TIME to >0, this value is used, rather than the recovery interval specified for the server instance.


Manual: CHECKPOINT [ checkpoint_duration ]
Description: Issued when you execute a Transact-SQL CHECKPOINT command. The manual checkpoint occurs in the current database for your connection. By default, manual checkpoints run to completion. Throttling works the same way as for automatic checkpoints. Optionally, the checkpoint_durationparameter specifies a requested amount of time, in seconds, for the checkpoint to complete.


Internal: None
Description: Issued by various server operations such as backup and database-snapshot creation to guarantee that disk images match the current state of the log.