Overview of Locking Mechanisms (310)

In general, multiuser databases use some form of data locking to solve the problems
associated with data concurrency, consistency, and integrity. Locks are mechanisms
that prevent destructive interaction between transactions accessing the same resource.
Resources include two general types of objects:
■ User objects, such as tables and rows (structures and data)
■ System objects not visible to users, such as shared data structures in the memory
and data dictionary rows

鎖機制
1. 鎖是一種防止多個事務訪問同一資源時產生破壞性的相互影響的機制
2. 這樣的資源可以分為兩類：
* 使用者物件,例如表及資料行
* 使用者不可見的系統物件,例如記憶體中的共享資料結構和資料字典中的資訊

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