What is MVCC (Multi-Version Concurrency Control)?

MVCC (Multi-Version Concurrency Control) is a method of managing concurrency in databases that allows multiple transactions to read and write data simultaneously without locks, while maintaining consistency.

The idea of MVCC is that when data is modified, existing records are not overwritten but new versions are created. Each transaction only sees the versions of data that were current at the start of the transaction, ensuring isolation and preventing conflicts.

For example, if one transaction reads a row and another modifies it, the first will see the old version, and the second will see the new one. This increases performance and reduces locking compared to traditional locking mechanisms.