Background documentationReader-Writer Lock Locate this document in the navigation structure

 

Reader-writer locks (share locks) are special semaphores used by the database system to synchronize both exclusive and non-exclusive access by tasks to critical sections of the working memory.

Special Synchronization Mechanisms

Name

Used for

Description

Region

Data Cache

EXCLUSIVE

When a task accesses a critical section, the associated region blocks this critical section for all other tasks.

Reader-writer lock

(share lock)

Catalog Cache

Shared SQL Cache

EXCLUSIVE or SHARED

If a task write-accesses a critical section, the associated reader-writer lock (share 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 (share lock) blocks this critical section for all other write-accesses but allows other read-accesses.

More Information

Concepts of the Database System, Working Memory Areas

SQL Reference Manual, SHARELOCKINFORMATION, SHARELOCKSTATISTICS, SHARELOCKWAITINGTASKS