Database locks

You can lock an entire database. The act of opening a database places a shared lock on the name of the database. A database is opened with the CONNECT, DATABASE, or CREATE DATABASE statements. As long as a program has a database open, the shared lock on the name prevents any other program from dropping the database or putting an exclusive lock on it.

The following statement shows how you might lock an entire database exclusively:

DATABASE database_one EXCLUSIVE

This statement succeeds if no other program has opened that database. After the lock is placed, no other program can open the database, even for reading, because its attempt to place a shared lock on the database name fails.

A database lock is released only when the database closes. That action can be performed explicitly with the DISCONNECT or CLOSE DATABASE statements or implicitly by executing another DATABASE statement.

Because locking a database reduces concurrency in that database to zero, it makes programming simple; concurrent effects cannot happen. However, you should lock a database only when no other programs need access. Database locking is often used before applying massive changes to data during off-peak hours.