I. Introduction

MVCC (Multi-Version Concurrency Control) is a technique used in databases to manage concurrent access to the database. MVCC allows multiple transactions to read and write data simultaneously without blocking each other, providing a high level of concurrency and performance.

In this article, we will explore how MVCC works in databases like PostgreSQL and MySQL and its benefits for developers and users.

II. How MVCC Works in Databases

MVCC works by creating multiple versions of a row in the database to represent different states of the data at different points in time. When a transaction updates a row, the database creates a new version of the row with the updated data, while keeping the old version intact. This allows other transactions to continue reading the old version of the row without being affected by the update.

When a transaction commits or rolls back, the database marks the old version of the row as obsolete and removes it from the database. This process is known as garbage collection and helps the database maintain a clean and efficient database.

MVCC uses a combination of read and write locks to ensure that transactions can read and write data concurrently without interfering with each other. Read locks allow transactions to read data without blocking other transactions, while write locks prevent multiple transactions from updating the same row simultaneously.

III. Alternatives solutions

There are other techniques used in databases to manage concurrent access, such as:

  • Locking: Locking is a technique that prevents other transactions from accessing data while a transaction is reading or writing it. Locking can lead to deadlocks and performance issues if not managed properly. Examples: MySQL (using InnoDB), Oracle .Database.

  • Timestamp Ordering: Timestamp ordering is a technique that assigns a unique timestamp to each transaction and uses these timestamps to determine the order in which transactions should be executed. Timestamp ordering can help prevent conflicts between transactions but may not provide the same level of concurrency as MVCC. Examples: Timesten, FoundationDB.

  • Two-Phase Locking: Two-phase locking is a technique that divides a transaction into two phases: a growing phase where locks are acquired and a shrinking phase where locks are released. Two-phase locking can help prevent conflicts between transactions but may not provide the same level of concurrency as MVCC. Examples: IBM Db2, Microsoft SQL Server.

IV. Conclusion

MVCC is a powerful technique used in databases like PostgreSQL and MySQL to manage concurrent access to the database. By creating multiple versions of rows and using read and write locks, databases provide a high level of concurrency and performance for developers and users. MVCC ensures that transactions can read and write data simultaneously without blocking each other, improving the responsiveness and efficiency of the system. Other techniques like locking, timestamp ordering, and two-phase locking are also used in databases to manage concurrent access, but MVCC remains a popular choice for its high level of concurrency and performance.