When a database shuts down cleanly, the database file holds a complete and current copy of all the data in the database. When a database is running, however, the database file is generally not current or complete.
The only time a database file is guaranteed to hold a complete and current copy of all data is immediately after a checkpoint completes. Following a checkpoint, all the contents of the database cache are on disk.
The database server checkpoints a database under the following conditions:
As part of the database shutdown operations
When the amount of time since the last checkpoint exceeds the setting of the -gc server option
When the estimated time to do a recovery operation exceeds the setting of the -gr server option
When the database server is idle long enough to write all dirty pages
When certain DDL statements (such as ALTER TABLE, DROP TABLE, DROP INDEX, LOAD TABLE, or BACKUP) are executed
When a connection issues a CHECKPOINT statement
When the database server is running without a transaction log and a transaction is committed
To ensure that you have a complete copy of all committed transactions between checkpoints, you need the database file and the transaction log.
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