Concurrency control

The database server threads that run on the same virtual processor and on separate virtual processors share access to resources in shared memory.

When a thread writes to shared memory, it uses mechanisms called mutexes and locks to prevent other threads from simultaneously writing to the same area. A mutex gives a thread the right to access a shared-memory resource. A lock prevents other threads from writing to a buffer until the thread that placed the lock is finished with the buffer and releases the lock.

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