1. PostgreSQL :
PostgreSQL 是一个强大的开源对象关系数据库系统。由于其高稳定性，它以低维护工作提供良好的性能。 PostgreSQL 是第一个实现多版本并发控制 (MVCC) 功能的 DBMS。
2. 亚马逊云搜索：
它是一种可扩展的基于云的搜索服务，是 Amazon Web Services 的一部分。它是亚马逊托管的搜索引擎服务，数据存储在亚马逊云中。该数据库支持 34 种语言，其特点是突出显示、自动完成和地理空间搜索。
PostgreSQL 和 Amazon CloudSearch 的区别：
| S.No. | PostgreSQL | Amazon CloudSearch |
|---|---|---|
| 1. | It is developed By PostgreSQL Global Development Group on 1989. | It is developed By Amazon in 2012. |
| 2. | It is Open Source. | It is commercial. |
| 3. | Server operating systems for PostgreSQL is FreeBSD, HP-UX, Linux, NetBSD, OpenBSD, OS X, Solaris, Unix, Windows. | Server operating systems for Amazon CloudSearch is hosted. |
| 4. | Its Primary database model is a Relational DBMS. | Its primary database model is a Search engine. |
| 5. | It has predefined data type such as date or float. | It also has has no predefined data type such as date or float. |
| 6. | It supports SQL. | It does not support SQL. |
| 7. | APIs and other access methods for PostgreSQL is ADO.NET, JDBC, native C library, ODBC, streaming API for large objects. | APIs and other access methods for Amazon CloudSearch is HTTP API. |
| 8. | It supports ACID properties. | It does not support ACID properties. |
| 9. | It supports Server-side scripting using user defined functions. | It does not support Server-side scripting. |
| 10. | It supports Triggers. | It does not support Triggers. |
| 11. | It supports Partitioning methods using partitioning by range, list and (since PostgreSQL 11) by hash. | It also supports Partitioning methods. |
| 12. | It provides the concept of Referential Integrity. Hence, there is Foreign Keys. | It does not provides the concept of Referential Integrity. Hence, there is no Foreign Keys. |