Administración de PostgreSQL
MVCC - Ejemplo (SQL)

alvh=> BEGIN;
BEGIN
alvh=> SELECT * FROM mvcc;
 a |    b    
---+---------
 1 | uno
(1 row)
                                     alvh=> BEGIN;
                                     BEGIN
alvh=> update mvcc set b='dos';
UPDATE 1
                                     alvh=> SELECT * FROM mvcc;
                                      a |  b  
                                     ---+-----
                                      1 | uno
                                     (1 row)
alvh=> COMMIT;
COMMIT
                                     alvh=> SELECT * FROM mvcc;
                                      a |  b  
                                     ---+-----
                                      1 | dos
                                     (1 row)
                                     alvh=> COMMIT;