Berkeley DB Reference Guide: Access Methods
Flushing the database cache
The DB->sync function is the standard function for flushing all modified records from the database cache to disk.
It is important to understand that flushing cached information to disk only minimizes the window of opportunity for corrupted data.
While unlikely, it is possible for database corruption to happen if a system or application crash occurs while writing data to the database. To ensure that database corruption never occurs, applications must either: use transactions and logging with automatic recovery, use logging and application-specific recovery, or edit a copy of the database, and, once all applications using the database have successfully called DB->close, use system operations (e.g., the POSIX 1003.1 rename system call) to atomically replace the original database with the updated copy.
