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.
更多改进内容请看：
http://developer.postgresql.org/pgdocs/postgres/release-9-1-alpha.html | 
