Why is UPDATE in PostgreSQL essentially a DELETE and INSERT?

In PostgreSQL, the UPDATE operation is often implemented as a sequence of DELETE and INSERT due to the characteristics of MVCC (Multi-Version Concurrency Control).

When an UPDATE occurs, PostgreSQL does not modify the row in place. Instead:

1. The old version of the row is marked as obsolete (DELETE).
2. A new version of the row with the updated data is created (INSERT).

This approach helps maintain data consistency for concurrent transactions and allows for rollback of changes. It improves performance and reliability when working with concurrent data access.