检查、剖析memcached运用状况

访问量上升，数据库压力大，怎样办？好办法是在中心挡一层缓存！这个缓存需求高效，不能比数据库慢，不然服务质量受影响；假如能把数据用hash打散存储到硬盘，也是能够的，不过在内存越来越廉价的今日，仍是运用内存吧！

    mysql也有自个的缓存，也是存储在内存的，但是有一个说法是：

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只能有一个实例

意味着你能存储内容的上限即是你服务器的可用内存，一台服务器能有多少内存？你又能存多少呢？

只需有写操作，mysql的query cache就失效

只需数据库内容稍有改动，那怕改动的是其他行，mysql的query cache也会失效

    再说，假如mysql都抗不住了，怎样还能盼望它供给的缓存呢？

    所以我能够运用memcached了！他的优点和如何用能够参阅：

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1：《Memcache和mysql交互流程操作原理》

2：《让memcached和mysql非常好的作业》

    开发时面对需求是个麻烦事，更绵长而堵心的是维护，所以我更关心的是memcached运行中的状况。还好的是，memcached的作者给咱们供给检查运行状况的指令。主要是“stats”，运用方法为 “telnet ip 端口号”，登录后运用“stats”指令。

    然后你能够看见很多内容，详细能够参阅：《memcacche stats》

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pid = process id

uptime = number of seconds since the process was started

time = current time

version = memcached version

rusage_user = seconds the cpu has devoted to the process as the user http://www.haomad.com 

rusage_system = seconds the cpu has devoted to the process as the system http://www.metabase.cn

curr_items = total number of items currently in memcache

total_items = total number of items that have passed through the cache

bytes = total number of bytes currently in use by curr_items

curr_connections = total number of open connections to memcached

connection_structures = ???

cmd_get = total GET commands issued to the server

cmd_set = total SET commands issued to the server

get_hits = total number of times a GET command was able to retrieve and

return data

get_misses = total number of times a GET command was unable to retrieve and

return data

bytes_read = total number of bytes input into the server

bytes_written = total number of bytes written by the server

limit_maxbytes = total storage bytes available to the server.

    着重说一下几个对观测很有用的项。