Concurrency Control Mechanisms in Distributed Databases

Concurrency control mechanisms ensure that multiple transactions executing simultaneously do not interfere with each other, maintaining data consistency and integrity. In distributed databases, where transactions run across multiple nodes, concurrency control becomes more complex due to network latency, replication, and potential system failures.

There are three primary concurrency control mechanisms:

  1. Lock-Based Concurrency Control

    • Uses locks to manage access to data items.
    • Two-Phase Locking (2PL) ensures serializability by requiring a transaction to acquire all necessary locks before releasing any.
    • Distributed locking mechanisms coordinate locks across multiple nodes but can cause deadlocks and performance bottlenecks.

  2. Timestamp-Based Concurrency Control

    • Assigns a unique timestamp to each transaction.
    • Transactions execute in timestamp order, preventing conflicts.
    • Multiversion Concurrency Control (MVCC) keeps multiple versions of data, allowing readers and writers to work simultaneously without blocking each other.

  3. Optimistic Concurrency Control (OCC)

    • Transactions execute without restrictions but undergo validation before committing.
    • If conflicts are detected, the transaction is rolled back and retried.
    • Suitable for applications with low contention and high read operations.

Each mechanism has trade-offs in terms of performance, consistency, and complexity, making their choice crucial for efficient distributed database management.