Transactions, Locking and Multi-user Support
Transactions and database locking support is built directly into Data Dictionaries. Database updates (saves and deletes) are, therefore, always multi-user safe. Managing transactions, locking, and multi-user access is automatic, requiring no programming effort from the developer.
Transaction rollback is also built into Data Dictionaries. If, for any reason, a save or delete transaction cannot be completed, the entire transaction is rolled back, and no changes are committed to the database.
Locks will be placed on your database during a transaction. The tables that participate in the transaction will be write-locked. This allows other users to read data from the tables but will not allow them to write data until the locks are released. Locks are released when a transaction has ended—either as a successful commit or a failed rollback. Depending on the database, the locks are applied at a record level or at a table level.
Transactions and locking are discussed in more detail in Transactions and DDOs.