MVCC in PostgreSQL Database

• 27 Apr, 2026
• 0 Comments
• 45 Secs Read

MVCC in PostgreSQL Database

MVCC (Multi-Version Concurrency Control) in PostgreSQL allows multiple users to access the same data without blocking each other.

Instead of locking rows, PostgreSQL keeps multiple versions of a row.

The Problem MVCC Solves

In traditional databases (lock-based systems):

• Read can block write
• Write can block read
• Leads to slow performance & waiting

PostgreSQL avoids this by:

• Never modifying rows in place
• Creating new versions of rows

 Why MVCC?

• Avoids read locks
• Improves performance
• Supports concurrent transactions

How MVCC Works (Concept)

When you update a row:

• Old row version is not deleted immediately
• New row version is created
• Each transaction sees data based on its snapshot

Key Internals

• Each row has:
  • xmin → transaction ID that created the row
  • xmax → transaction ID that deleted/updated the row

SELECT xmin, xmax, * FROM student_mvcc;

VACUUM emp;