PostgreSQL

With more than 15 years of active development, PostgreSQL is another stellar open source option, running on all major operating systems, including Linux, UNIX (AIX, BSD, HP-UX, SGI IRIX, Mac OS X, Solaris, Tru64), and Windows. PostgreSQL is also fully ACID (Atomicity, Consistency, Isolation, Durability) compliant.

Pros

• Create custom data types and query methods
• Framework enables definition and creation of own custom data types
• Runs stored procedures in more than a dozen programming languages:
  • Java, Perl, Python, Ruby, Tcl, C/C++, and its own PL/pgSQL
• GiST (Generalized Search Tree) system
  • Brings together different sorting and searching algorithms:
    • B-tree, B+-tree, R-tree, partial sum trees, and ranked B+-trees
  • Creation of extensions like CitusDB for more parallelism without modifying Postgres code

Cons

• MVCC system requires regular “vacuuming”
  • Problems in high transaction rate environments
• Development is done by broad community
  • Fair amount of effort for improvements added