PostgreSQL is a powerful, open source relational database system. It has more than 15 years of active development and a proven architecture that has earned it a strong reputation for reliability, data integrity, and correctness.
One of the PostgreSQL's most sophisticated features is so called Multi-Version Concurrency Control (MVCC), a standard technique for avoiding conflicts between reads and writes of the same object in database. MVCC guarantees that each transaction sees a consistent view of the database by reading non-current data for objects modified by concurrent transactions. Thanks to MVCC, PostgreSQL has great scalability, a robust hot backup tool and many other nice features comparable to the most advanced commercial databases.