What is MVCC in PostgreSQL and how does it work?

MVCC (Multi-Version Concurrency Control) is PostgreSQL's method of handling concurrent access to data.

How it works:
• Each transaction sees a snapshot of data
• Multiple versions of rows can exist simultaneously
• Readers don't block writers and vice versa
• Uses transaction IDs (xmin, xmax) to track row versions
• VACUUM process cleans up old row versions

Benefits:
• High concurrency
• No read locks
• Consistent data views
• Better performance under load