PostgreSQL is free and open source software. Its source code is available under PostgreSQL license, a liberal open source license. You are free to use, modify and distribute PostgreSQL in any form.
PostgreSQL requires very minimum maintained efforts because of its stability. Therefore, if you develop applications based on PostgreSQL, the total cost of ownership is low in comparison with other database management systems
What make PostgreSQL stand out
-multi-version concurrency control (MVCC) feature
-It allows you to add custom functions developed using different programming languages such as C/C++, Java, etc.
-you can define your own data types, index types, functional languages, etc.
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