关于 Memcached
memcached 是一种高性能、分布式内存对象缓存系统，本质上是通用的，但最初旨在通过减轻数据库负载来加速动态 Web 应用程序。
您可以将其视为应用程序的短期记忆.
它能做什么
memcached 允许您从系统中超出您需要的部分获取内存，并使其可供您拥有少于您需要的区域访问.
memcached 还允许您更好地利用内存。如果您考虑右图，您可以看到两种部署方案:
- 每个节点都是完全独立的（上面）.
- 每个节点都可以使用其他节点的内存（下面）.
第一种情况说明了经典的部署策略，然而你会发现这既是一种浪费，因为总的缓存大小只是你的web农场实际容量的一小部分，而且还需要花费大量的精力来保持所有这些节点上的缓存一致.
使用 memcached，您可以看到所有服务器都在查找相同的虚拟内存池。这意味着给定项目始终存储并始终从整个 Web 集群中的同一位置检索.
此外，随着对应用程序的需求增长到需要更多服务器的程度，通常在必须定期访问的数据方面也会增长。系统的这两个方面一起扩展的部署策略才有意义.
为简单起见，右图仅显示了两个 Web 服务器，但随着数量的增加，属性保持不变。如果您有 50 个 Web 服务器，在第一个示例中您的可用缓存大小仍为 64MB，但在第二个示例中，您将有 3.2GB 的可用缓存.
当然，您不需要将 Web 服务器的内存用于缓存。许多 memcached 用户拥有专为 memcached 服务器而构建的专用机器.
起源
Memcached 最初是由 Brad Fitzpatrick 于 2003 年为LiveJournal开发的.
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