How is transaction integrity and reliability ensured in PostgreSQL?

In PostgreSQL, the integrity and reliability of transaction execution are ensured by supporting ACID properties (Atomicity, Consistency, Isolation, Durability):

• Atomicity: a transaction is executed completely or not at all. If an error occurs, all changes are rolled back.
• Consistency: after the transaction, the database remains in a correct state, adhering to all constraints and rules.
• Isolation: concurrent transactions do not affect each other, achieved through isolation levels and locks.
• Durability: once a transaction is committed, its changes are saved even in case of failures, thanks to write-ahead logging.

PostgreSQL uses MVCC (Multi-Version Concurrency Control) to manage concurrency and transaction isolation, allowing efficient handling of simultaneous operations without read locks.

Example of a transaction in Python with psycopg2:

import psycopg2

conn = psycopg2.connect(...)
try:
    with conn:
        with conn.cursor() as cur:
            cur.execute("INSERT INTO users(name) VALUES(%s)", ('Alice',))
            # other operations
except Exception as e:
    print(f"Transaction error: {e}")
finally:
    conn.close()

In this example, if an error occurs, all changes within the transaction block are rolled back.