A critical section is a memory area to which different tasks have competing access and where access is controlled by synchronization mechanisms.
To control exclusive access by tasks to critical regions, the database system uses special semaphores, which are called regions. When a task accesses a critical section, the associated region blocks this critical section for all other tasks.
To control both exclusive and non-exclusive access to critical sections, the database system uses regions with extended functionality, called reader-writer locks.
If a task write-accesses a critical section, the associated reader-writer lock blocks this critical section for all other write-accesses but allows other read-accesses.
If a task read-accesses a critical section, the associated reader-writer lock blocks this critical section for all other write-accesses but allows other read-accesses.
Blocking critical sections has nothing to do with the SQL locks on database objects.
See also:
Database
Administration in CCMS: Critical
Sections