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Thus concurrency control is an essential element for correctness in any system where two database transactions or more, executed with time overlap, can access the same data, e.g., virtually in any general-purpose database system.
Multiversion concurrency control (MCC or MVCC), is a non-locking concurrency control method commonly used by database management systems to provide concurrent access to the database and in programming languages to implement transactional memory.
Each object in the database is given two timestamp fields which are not used other than for concurrency control: R T ( O j ) {\displaystyle RT(O_{j})} is the timestamp of the last transaction that read the value of the object ( T S ( T r ) {\displaystyle TS(T_{r})} , where T r {\displaystyle T_{r}} is the last transaction that read the value of ...
In databases and transaction processing, two-phase locking (2PL) is a pessimistic concurrency control method that guarantees conflict-serializability. [1] [2] It is also the name of the resulting set of database transaction schedules (histories).
[6] Parallelism vs concurrency; Multi-threading and multi-processing (shared system resources) Synchronization (coordinating access to shared resources) Coordination (managing interactions between concurrent tasks) Concurrency Control (ensuring data consistency and integrity) Inter-process Communication (IPC, facilitating information exchange)
Schedules are fundamental concepts in database concurrency control theory. In practice, most general purpose database systems employ conflict-serializable and strict recoverable schedules. In practice, most general purpose database systems employ conflict-serializable and strict recoverable schedules.
Optimistic concurrency control (OCC), also known as optimistic locking, is a non-locking concurrency control method applied to transactional systems such as relational database management systems and software transactional memory. OCC assumes that multiple transactions can frequently complete without interfering with each other.
This definition is probably the broadest such definition possible in the context of database concurrency control, and it makes CO together with any of its (useful: No concurrency control information distribution) generalizing variants (Vote ordering (VO); see CO variants below) the necessary condition for Global serializability (i.e., the union ...