what is concurrency control in dbms
Concurrency Control in DBMS
Concurrency Control in DBMS (Database Management System) refers to the mechanism employed to ensure the consistency, integrity, and isolation of concurrent transactions in a multi-user database environment. In simpler terms, it is the process of managing and coordinating multiple transactions that are accessing or modifying the same data concurrently.
In a DBMS, multiple users or applications may simultaneously access or modify the data stored in the database. However, this concurrent access can lead to various issues, such as data inconsistency, lost updates, and conflicts. Concurrency control techniques are implemented to address these problems and maintain the overall integrity and reliability of the database.
One of the fundamental challenges of concurrency control is the occurrence of conflicts when two or more transactions attempt to access or modify the same data simultaneously. These conflicts can be categorized into three types: read-write conflicts (one transaction reads while another writes), write-write conflicts (two or more transactions attempt to write to the same data), and write-read conflicts (one transaction writes while another reads).
To handle these conflicts, DBMS employs different concurrency control mechanisms. One widely used technique is the locking-based approach, where locks are used to control access to data items. When a transaction wants to read or modify a data item, it first requests a lock on that item. The lock ensures that no other transaction can access or modify the data until the lock is released. This way, conflicts are avoided, and data consistency is maintained.
There are two types of locks commonly used in concurrency control: shared locks (read locks) and exclusive locks (write locks). Shared locks allow multiple transactions to read the data simultaneously but prevent any transaction from modifying it. On the other hand, exclusive locks allow only one transaction to modify the data while preventing other transactions from reading or modifying it.
Another approach to concurrency control is optimistic concurrency control. In this technique, conflicts are detected and resolved after the transactions have completed their execution. Each transaction is allowed to proceed without acquiring locks, and only during the commit phase, conflicts are checked. If conflicts are detected, appropriate actions are taken to resolve them, such as rolling back one of the conflicting transactions.
Concurrency control also ensures transaction isolation, which means that each transaction is executed as if it were the only transaction running on the system. Isolation levels, such as Read Uncommitted, Read Committed, Repeatable Read, and Serializable, determine the level of isolation provided by the DBMS.
In conclusion, concurrency control in DBMS is a crucial aspect of managing concurrent transactions in a multi-user database environment. By implementing appropriate mechanisms like locking or optimistic concurrency control, conflicts are minimized, data consistency is maintained, and the overall reliability and integrity of the database are upheld.
In a DBMS, multiple users or applications may simultaneously access or modify the data stored in the database. However, this concurrent access can lead to various issues, such as data inconsistency, lost updates, and conflicts. Concurrency control techniques are implemented to address these problems and maintain the overall integrity and reliability of the database.
One of the fundamental challenges of concurrency control is the occurrence of conflicts when two or more transactions attempt to access or modify the same data simultaneously. These conflicts can be categorized into three types: read-write conflicts (one transaction reads while another writes), write-write conflicts (two or more transactions attempt to write to the same data), and write-read conflicts (one transaction writes while another reads).
To handle these conflicts, DBMS employs different concurrency control mechanisms. One widely used technique is the locking-based approach, where locks are used to control access to data items. When a transaction wants to read or modify a data item, it first requests a lock on that item. The lock ensures that no other transaction can access or modify the data until the lock is released. This way, conflicts are avoided, and data consistency is maintained.
There are two types of locks commonly used in concurrency control: shared locks (read locks) and exclusive locks (write locks). Shared locks allow multiple transactions to read the data simultaneously but prevent any transaction from modifying it. On the other hand, exclusive locks allow only one transaction to modify the data while preventing other transactions from reading or modifying it.
Another approach to concurrency control is optimistic concurrency control. In this technique, conflicts are detected and resolved after the transactions have completed their execution. Each transaction is allowed to proceed without acquiring locks, and only during the commit phase, conflicts are checked. If conflicts are detected, appropriate actions are taken to resolve them, such as rolling back one of the conflicting transactions.
Concurrency control also ensures transaction isolation, which means that each transaction is executed as if it were the only transaction running on the system. Isolation levels, such as Read Uncommitted, Read Committed, Repeatable Read, and Serializable, determine the level of isolation provided by the DBMS.
In conclusion, concurrency control in DBMS is a crucial aspect of managing concurrent transactions in a multi-user database environment. By implementing appropriate mechanisms like locking or optimistic concurrency control, conflicts are minimized, data consistency is maintained, and the overall reliability and integrity of the database are upheld.
