Concurrency Control in DBMS

Concurrency control refers to the mechanisms and techniques employed to manage simultaneous access to the database by multiple users or transactions. The primary goal is to ensure that transactions execute correctly and consistently, even when executed concurrently. This involves coordinating the execution order of transactions, managing locks on data items, and resolving conflicts that may arise due to concurrent access.

In the below PDF we discuss about Concurrency Control in DBMS in detail in simple language, Hope this will help in better understanding.

Techniques of Concurrency Control:

1. Locking:

One of the most fundamental techniques, locking involves acquiring locks on data items to prevent other transactions from accessing them concurrently. This can be further classified into two types:

  • Exclusive Locks (Write Locks): Prevent other transactions from reading or writing to the locked data item.
  • Shared Locks (Read Locks): Allow multiple transactions to read the locked data item but prevent any transaction from writing to it.

2. Timestamp Ordering:

Each transaction is assigned a unique timestamp, and transactions are ordered based on these timestamps. This technique ensures serializability by allowing transactions to proceed only if they don’t conflict with each other based on their timestamps.

3. Optimistic Concurrency Control:

This approach assumes that conflicts between transactions are rare. Transactions proceed without locking, but before committing, they check if any other transaction has modified the same data. If a conflict is detected, appropriate actions are taken to resolve it.

Importance of Concurrency Control:

In today’s dynamic environments, where databases are accessed by numerous users concurrently, ensuring data consistency is imperative. Here’s why concurrency control is crucial:

  • Data Integrity: By preventing conflicting operations from interfering with each other, concurrency control maintains the integrity of the database. It ensures that transactions produce accurate and meaningful results.
  • Isolation: Concurrency control ensures that each transaction operates in isolation from others, preserving the illusion that it is executing alone on the database. This prevents interference between transactions, reducing the likelihood of data corruption.
  • Performance Optimization: While ensuring data consistency, concurrency control also aims to maximize system throughput and minimize transaction latency. Efficient concurrency control mechanisms enable better utilization of system resources and improve overall performance.
  • Scalability: Proper concurrency control mechanisms facilitate scalability by allowing multiple users to access the database simultaneously without sacrificing performance or data integrity. This is crucial for systems handling large volumes of transactions.


In Conclusion, Concurrency control is a fundamental aspect of DBMS that ensures data integrity and consistency in multi-user environments. By coordinating concurrent access to the database, it enables efficient transaction processing while mitigating conflicts and preserving data correctness. Understanding the principles and techniques of concurrency control is essential for designing robust and scalable database systems that meet the demands of modern applications.

Related Question

Concurrency control in a Database Management System (DBMS) refers to the techniques used to ensure that multiple transactions can execute concurrently without causing inconsistencies in the database.

Concurrency control is essential to maintain the integrity of the database by preventing issues such as lost updates, uncommitted data, and inconsistent reads, which can occur when multiple transactions access and modify the same data simultaneously.

Concurrency control addresses problems such as lost updates, dirty reads, non-repeatable reads, and phantom reads, which can occur when multiple transactions access and modify data concurrently.

The common isolation levels provided by concurrency control mechanisms are Read Uncommitted, Read Committed, Repeatable Read, and Serializable, each offering a different level of consistency and isolation for concurrent transactions.

Popular concurrency control techniques include locking (e.g., exclusive locks, shared locks), timestamp-based protocols, optimistic concurrency control, multiversion concurrency control (MVCC), and two-phase locking.


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