Why is the 'Read Uncommitted' read mode absent in PostgreSQL?

There is no "Read Uncommitted" transaction isolation level in PostgreSQL for several reasons:

• PostgreSQL implements the MVCC (Multi-Version Concurrency Control) model, which provides isolation at the "Read Committed" level and above. This prevents dirty reads without the need for a "Read Uncommitted" mode.
• "Read Uncommitted" allows reading uncommitted data, which can lead to unstable and inconsistent results. PostgreSQL does not support this level of isolation because it contradicts the principles of MVCC.
• Instead of "Read Uncommitted," the minimum isolation level in PostgreSQL is "Read Committed," which guarantees that a transaction only sees committed data.

Thus, the absence of "Read Uncommitted" is related to the MVCC architecture and the goal of ensuring data correctness and consistency.