memcachedb

memcachedb是为了持久化而产生的一个分布式 "key-value"存储系统，你可以认为是memcached+berkeley DB+sina的一些东西的一个集成，这个东西主要是为了提高持久化对象的访问效率，而不是一个缓存，他的特点是：

        比传统的RDBMS速度快效率高

        高并发环境下访问安全可靠，效率很不错

        存储的数据比较小

 

         总之：高效、安全的事物机制、memcached的分布式协议支持

是他的几大亮点.

 

你可以将一些数据量不大，读写却很频繁的数据放再这里面，而不用往mysql等数据库里写，据说“sohu”的在线用户是存在这里面的，可见这东西还是挺可靠的。

          在官方文档里明确指出，只提倡用此数据库保存如下类型的数据： 

Index, Counter, Flags
Identity Management(Account, Profile, User config info, Score)
Messaging
Personal domain name
meta data of distributed system
Other non-relatonal data

.......................

 

即，要求访问数据快、数据量不大，并且需要持久化到数据库中，却不需要sql查询的数据.

                 

        下面我们来说应用：

如果你看过了上一片文章，并且已经成功安装memcachedb的话，那么，现在请启动你的memcachedb,命令如下：

memcachedb -p21201 -d -r -u root -f 21201.db -H /data1/demo  -N -P /data1/logs/21201.pid

参数说明如下：

 

‘-p <num>’ TCP port number to listen on (default: 21201)       tcp侦听端口

   
‘-l <ip addr>’ interface to listen on, default is INDRR ANY      这个不要管他

‘-d’ run as a daemon    作为隐藏的线程运行

‘-r’ maximize core file limit 
‘-u <username>’ assume identity of <username> (only when run as root) 用户名

‘-c <num>’ max simultaneous connections, default is 1024 
‘-b <num>’ max item buffer size in bytes, default is 1KB
‘-v’ verbose (print errors/warnings while in event loop)
‘-vv’ very verbose (also print client commands/reponses)
‘-P <file>’ save PID in <file>, only used with -d option

 

‘-m <num>’ in-memmory cache size of BerkeleyDB in megabytes, default
is 64MB
‘-f <file>’ filename of database, default is
/data1/memcachedb/default.db
‘-H <dir>’ env home of database, default is /data1/memcachedb
‘-L <num>’ log buffer size in kbytes, default is 32KB
‘-C <num>’ do checkpoint every XX seconds, 0 for disable, default is 60s
‘-D <num>’ do deadlock detecting every XXX millisecond, 0 for disable,
default is 100ms
‘-N’ enable DB TXN NOSYNC to gain big performance
improved, default is off

 

如果你想要将数据保存再特定的目录可以使用-H 但是你必须首先要创建该目录，否则数据库将不可启动

      现在我们来测试下memcachedb是否已经启动了：

输入  telnet 'your ip'  端口号 （默认21201）

telnet 127.0.0.1 21201

Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is ’^]’.

如果可以连接，证明已经启动，现在我们可以来联系下memcached的命令了,呵呵.

 

以下是memcachedb支持的命令：

‘get’ Retrieval of one or multiple items
‘set’ ”Store this data”
‘add’ ”Store this data, but only if the server *doesn’t* already
 hold data for this key”
‘replace’ ”Store this data, but only if the server *does* already hold
data for this key”
‘delete’ deletes one item based a key
‘incr/decr’ Increment or decrement a numeric value. It’s atomic!
‘stats’ shows the status of current deamon. ’stats’, ’stats malloc’,
’stats maps’
Steve

 

 

   ‘db checkpoint’ does a checkpoint manuanlly.
‘db archive’ removes log files that are no longer needed.
‘stats bdb’ shows the status of BerkeleyDB.
‘rep ismaster’ shows whether the site is a master.
‘rep whoismaster’ shows which site is a master.
‘rep set priority’ sets the priority of a site for electing in replication.
‘rep set ack policy’ sets ACK policy of the replication.
‘rep set ack timeout’ sets ACK timeout value of the replication .
‘rep set bulk’ Enable bulk transfer or not in replication.
‘rep set request’ sets the minimum and maximum number of missing
log records that a client waits before requesting
retransmission.
‘stats rep’ shows the status of Replication.