今天听了香菜同学的对我们网站所使用的UDAS（Uniform. Data Access Source，统一数据访问源头）的介绍，对UDAS认识更多了一些。其中提到了Berkeley DB (BDB) 、OSCache、FlexCache这样的一些缓存方案，简单Google了解了一下，下面简单介绍一下吧。 我们应用服务器的UDAS可分为：Berkeley DB (BDB) 、OSCache、FlexCache 这三部分。而，我们的远程UDAS包括：Berkeley DB (BDB) 、OSCache两部分。 Berkeley DB (BDB) 中存储Key-Value性质的、数据量稍微较大、对性能要求较高的数据，如AV认证、深度认证的信息；而OSCache中存储及时丢失也关系不大、数据量也不大、性能要求也较高的数据，如统一的Session。Berkeley DB (BDB) is a computer software library that provides a high-performance embedded database, with bindings in C, C++, PHP, Java, Perl, Python,
Ruby, Tcl, Smalltalk, and other programming languages. BDB stores arbitrary key/data pairs as byte arrays, and supports multiple data items for a single key. BDB can support thousands of simultaneous threads of control or concurrent processes manipulating databases as large as 256 terabytes, on a wide variety of operating systems including most Unix-like and
Windows systems, and real-time operating systems.
更多地：http://www.oracle.com/technetwork/database/berkeleydb/overview/index.html
OSCache is "a Java framework" developed by OpenSymphony that makes it easy to
cache content in Web applications.
According to OpenSymphony, OSCache
* is a caching solution that includes a JSP tag library and set of classes to perform. fine grained dynamic caching of JSP content, servlet responses or arbitrary objects.
* provides both in memory and persistent on disk caches.
* can allow your site to have graceful error tolerance (eg if an error occurs like your db goes down, you can serve the cached content so people can still surf the site almost without knowing).
更多地：http://www.opensymphony.com/oscache/
FlexCache software creates a caching layer in your storage infrastructure that automatically adapts to changing usage patterns, eliminating performance bottlenecks.
In addition, FlexCache automatically replicates and serves hot data sets anywhere in your infrastructure using local caching volumes. This is useful for:
* Compute-intensive applications such as movie rendering, electronic design automation, seismic analysis, and financial markets simulation
* Software development and testing in distributed environments
* Automated tiered storage, where all data resides on inexpensive SATA disks and is cached on faster disks as needed
When used for remote caching, FlexCache simplifies file distribution and reduces your overall data management and WAN bandwidth costs.
更多地：http://www.netapp.com/us/products/platform-os/flexcache/
