PostgreSQL是一种特性非常齐全的">自由软件的对象-关系型数据库管理系统（ORDBMS），可以说是目前世界上最先进，功能最强大的自由数据库管理系统。 PostgreSQL是以加州大学伯克利分校计算机系开发的 POSTGRES，版本 4.2为基础的对象关系型数据库管理系统（ORDBMS）。 POSTGRES 领先的许多概念只是在非常迟的时候才出现在商业数据库中。
PostgreSQL支持大部分 SQL标准并且提供了许多其他现代特性：复杂查询、外键、触发器、视图、事务完整性、多版本并发控制。同样，PostgreSQL 可以用许多方法扩展，比如， 通过增加新的数据类型、函数、操作符、聚集函数、索引方法、过程语言。并且，因为许可证的灵活，任何人都可以以任何目的免费使用，修改，和分发 PostgreSQL， 不管是私用，商用，还是学术研究使用。
PostgreSQL alpha releases are snapshots of development code. They are intended to preview and test upcoming features and to provide the possibility for early feedback. They should not be used in production installations or active development projects. While the PostgreSQL code is continuously subject to a number of automated and manual tests, alpha releases might have serious bugs. Also features may be changed incompatibly or removed at any time during the development cycle.
The development cycle of a PostgreSQL major release alternates between periods of development and periods of integration work, called commit fests, normally one month each. Alpha releases are planned to be produced at the end of every commit fest, thus every two months. Since the first commit fest starts within a month from the beginning of development altogether, early alpha releases are not indicative of the likely feature set of the final release.
The release notes below highlight user visible changes and new features. There are normally numerous bug fixes and performance improvements in every new snapshot of PostgreSQL, and it would be too bulky to attempt to list them all. Note that many bug fixes are also backported to stable releases of PostgreSQL, and you should be using those if you are looking for bug-fix-only upgrades for your current installations.
These notes are cumulative over all alpha releases of the current development cycle. Items that are new in the latest alpha release are emphasized.
与 alpha2 版本比较，alpha3 的改进内容包括：
* KNN GiST, which implements order-by-operator support for GiST and optimizes nearest-neighbor geographic searches. This will power the next release of PostGIS.
* Additional instrumentation and monitoring facilities, including checkpoint introspection and last-WAL-timestamp information for replication.
* 增加一些新的内建函数: format(), pg_describe_object(), as well as pg_read_binary_file(), which will support the Extensions feature.
* 新的 libpq 函数: PQping(), PQlibVersion()
* Windows 下支持崩溃数据dump
* 新的 auth_delay 模块使得基于字典的攻击更加困难
* Security hooks on object creation, to support SEPostgres.