【IT168 专稿】Redis是一个开源的使用ANSI C语言编写、支持网络、可基于内存亦可持久化的日志型、Key-Value数据库，并提供多种语言的API。从2010年3月15日起，Redis的开发工作由VMware主持。本文将介绍Redis的高级实用特性。
安全性
设置客户端连接后进行任何其他指定前需要使用的密码。
下面我们做一个实验，说明redis的安全性是如何实现的。
requirepass beijing
我们设置了连接的口令是beijing
那么们启动一个客户端试一下:
redis 127.0.0.1:6379> keys *
(error) ERR operation not permitted
redis 127.0.0.1:6379>
说明权限太小，我们可以当前的这个窗口中设置口令
OK
redis 127.0.0.1:6379> keys *
1) "name"
redis 127.0.0.1:6379>
我们还可以在连接到服务器期间就指定一个口令，如下:
redis 127.0.0.1:6379> keys *
1) "name"
redis 127.0.0.1:6379>
可以看到我们在连接的时候就可以指定一个口令。
${PageNumber}主从复制
redis主从复制配置和使用都非常简单。通过主从复制可以允许多个slave server拥有和master server相同的数据库副本。
1、redis主从复制特点:
(1)、master可以拥有多个slave
(2)、多个slave可以连接同一个master外，还可以连接到其他slave
(3)、主从复制不会阻塞master，在同步数据时，master可以继续处理client请求
(4)、提高系统的伸缩性
2、redis主从复制过程:
当配置好slave后，slave与master建立连接，然后发送sync命令。无论是第一次连接还是重新连接，master都会启动一个后台进程，将数据库快照保存到文件中，同时master主进程会开始收集新的写命令并缓存。后台进程完成写文件后，master就发送文件给slave，slave将文件保存到硬盘上，再加载到内存中，接着master就会把缓存的命令转发给slave，后续master将收到的写命令发送给slave。如果master同时收到多个slave发来的同步连接命令，master只会启动一个进程来写数据库镜像，然后发送给所有的slave。
3、如何配置
配置slave服务器很简单，只需要在slave的配置文件中加入如下配置
下面我们做一个实验来演示如何搭建一个主从环境:
slaveof localhost 6379
我们在一台机器上启动主库(端口6379)，从库(端口6378)
启动后主库控制台日志如下:
[7064] 09 Aug 20:13:12 * Server started, Redis version 2.2.12
[7064] 09 Aug 20:13:12 # WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect.
[7064] 09 Aug 20:13:12 * The server is now ready to accept connections on port 6379
[7064] 09 Aug 20:13:13 - 0 clients connected (0 slaves), 539512 bytes in use
[7064] 09 Aug 20:13:18 - 0 clients connected (0 slaves), 539512 bytes in use
[7064] 09 Aug 20:13:20 - Accepted 127.0.0.1:37789
[7064] 09 Aug 20:13:20 * Slave ask for synchronization
[7064] 09 Aug 20:13:20 * Starting BGSAVE for SYNC
[7064] 09 Aug 20:13:20 * Background saving started by pid 7067
[7067] 09 Aug 20:13:20 * DB saved on disk
[7064] 09 Aug 20:13:20 * Background saving terminated with success
[7064] 09 Aug 20:13:20 * Synchronization with slave succeeded
[7064] 09 Aug 20:13:23 - 0 clients connected (1 slaves), 547380 bytes in use
启动后从库控制台日志如下:
[7066] 09 Aug 20:13:20 * Server started, Redis version 2.2.12
[7066] 09 Aug 20:13:20 # WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect.
[7066] 09 Aug 20:13:20 * The server is now ready to accept connections on port 6378
[7066] 09 Aug 20:13:20 - 0 clients connected (0 slaves), 539548 bytes in use
[7066] 09 Aug 20:13:20 * Connecting to MASTER...
[7066] 09 Aug 20:13:20 * MASTER <-> SLAVE sync started: SYNC sent
[7066] 09 Aug 20:13:20 * MASTER <-> SLAVE sync: receiving 10 bytes from master
[7066] 09 Aug 20:13:20 * MASTER <-> SLAVE sync: Loading DB in memory
[7066] 09 Aug 20:13:20 * MASTER <-> SLAVE sync: Finished with success
[7068] 09 Aug 20:13:20 * SYNC append only file rewrite performed
[7066] 09 Aug 20:13:20 * Background append only file rewriting started by pid 7068
[7066] 09 Aug 20:13:21 * Background append only file rewriting terminated with success
[7066] 09 Aug 20:13:21 * Parent diff flushed into the new append log file with success (0 bytes)
[7066] 09 Aug 20:13:21 * Append only file successfully rewritten.
[7066] 09 Aug 20:13:21 * The new append only file was selected for future appends.
[7066] 09 Aug 20:13:25 - 1 clients connected (0 slaves), 547396 bytes in use
我们在主库上设置一对键值对
OK
redis 127.0.0.1:6379>
在从库上取一下这个键
"HongWan"
redis 127.0.0.1:6378>
说明主从是同步正常的.
那么我们如何判断哪个是主哪个是从呢?我们只需调用info这个命令就可以得到主从的信息了,我们在从库上执行info命令
.
.
.
role:slave
master_host:localhost
master_port:6379
master_link_status:up
master_last_io_seconds_ago:10
master_sync_in_progress:0
db0:keys=1,expires=0
redis 127.0.0.1:6378>
里面有一个角色标识,来判断是主库还是从库,对于本例是一个从库，同时还有一个master_link_status用于标明主从是否异步，如果此值=up，说明同步正常;如果此值=down，说明同步异步;
db0:keys=1,expires=0， 用于说明数据库有几个key,以及过期key的数量。
