关于 Memcached
memcached 是一种高性能的分布式内存对象缓存系统，具有通用性，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内存。
它能做什么
memcached 允许您从系统中内存充足的部分获取内存，并将其提供给内存不足的区域。
memcached 还允许您更好地利用内存。如果您考虑右侧的图表，您可以看到两种部署场景
- 每个节点完全独立（顶部）。
- 每个节点都可以利用其他节点的内存（底部）。
第一个场景说明了经典的部署策略，但是您会发现它既浪费，因为总缓存大小只是您 Web 服务器场实际容量的一小部分，而且在保持所有这些节点之间缓存一致性方面也需要付出很多努力。
使用 memcached，您可以看到所有服务器都在查看同一个虚拟内存池。这意味着给定项始终存储在整个 Web 集群中的相同位置，并且始终从该位置检索。
此外，随着应用程序需求的增长，您需要更多服务器，通常也需要更多需要定期访问的数据。将系统这两个方面一起扩展的部署策略是有意义的。
右侧的插图仅显示了两个 Web 服务器，为了简单起见，但随着数量的增加，属性保持不变。如果您有 50 个 Web 服务器，第一个示例中可用的缓存大小仍然为 64MB，但在第二个示例中，可用的缓存大小为 3.2GB。
当然，您不需要使用 Web 服务器的内存作为缓存。许多 memcached 用户拥有专门的机器，这些机器专门用作 memcached 服务器。
起源
Memcached 最初由 Brad Fitzpatrick 于 2003 年为 LiveJournal 开发。
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