# Some Popular Database Systems

There are some big, expensive, **enterprise** database systems like Oracle, IBM DB2 Universal Database, Sybase etc.

They have lots of features, work on multiple platforms and can scale to multiple machines.

There are other database systems like MySQL Server that have lots of features and decent performance, but are relatively cheaper. However, MySQL Server only runs on Windows platform.

On the other hand, there are systems like MS Access that are cheap, easy to use but have limited functionality.

The following are some **open-source** database systems:

* **MySQL**
  * Limited SQL, not good for OLAP
  * Limited transaction support but fast lookups
  * Extremely widely used, e.g., web servers (Linux Apache MySQL PHP - LAMP)
* **PostgreSQL**
  * Rich SQL features, decent query optimizer
  * Not as widely used but popular in academia
* **SQLite**
  * SQL transactional DB
  * server-less
  * self-contained
  * zero-configuration
* **Berkeley DB**
  * No SQL support
  * Embedded database, a few hundred KB size
  * Basically a library of disk-based data structures with support for transactions
* **MapReduce, BigTable, PNuts, Dynamo, and others**
  * No SQL support
  * Used for data and text analysis (search engines etc) or to keep live data


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