cacheServer memcache / varnish / redis
memcache downloadhttp://cloud.github.com/downloads/libevent/libevent/libevent-2.0.15-stable.tar.gz
http://code.jellycan.com/files/memcached-1.2.6.tar.gz
http://code.jellycan.com/files/memcached-1.2.6-win32-bin.zip
http://hi.baidu.com/loveyoursmile/blog/item/1177312af38429335243c16f.html
http://www.urielkatz.com/archive/detail/memcached-64-bit-windows/
http://www.urielkatz.com/projects/memcached-win64/memcached-win64.zip
在64位Linux上安装MemCached
http://www.ningoo.net/html/2009/install_memcached_on_linux_64.html
命令行启动memcache服务
# /usr/local/bin/memcached -d -u root -m 1024 -l 192.168.100.149 -p 11211
# crontab -l
00 00 * * * /nmon/nmon_x86_rhel45 -s60 -c1440 -f -m /nmon
命令行查看memcache状态
http://www.51testing.com/?uid-116228-action-viewspace-itemid-107545
memcache的运行状态可以方便的用stats命令显示。
首先用telnet 127.0.0.1 11211这样的命令连接上memcache，然后直接输入stats就可以得到当前memcache的状态。
这些状态的说明如下：
pidmemcache服务器的进程IDuptime服务器已经运行的秒数time服务器当前的unix时间戳versionmemcache版本pointer_size当前操作系统的指针大小（32位系统一般是32bit）rusage_user进程的累计用户时间rusage_system进程的累计系统时间curr_items服务器当前存储的items数量total_items从服务器启动以后存储的items总数量bytes当前服务器存储items占用的字节数curr_connections当前打开着的连接数total_connections从服务器启动以后曾经打开过的连接数connection_structures服务器分配的连接构造数cmd_getget命令（获取）总请求次数cmd_setset命令（保存）总请求次数get_hits总命中次数get_misses总未命中次数evictions为获取空闲内存而删除的items数（分配给memcache的空间用满后需要删除旧的items来得到空间分配给新的items）bytes_read总读取字节数（请求字节数）bytes_written总发送字节数（结果字节数）limit_maxbytes分配给memcache的内存大小（字节）threads当前线程数 $ /usr/local/bin/memcached -h
memcached 1.4.5
-p <num> TCP port number to listen on (default: 11211)
-U <num> UDP port number to listen on (default: 11211, 0 is off)
-s <file> UNIX socket path to listen on (disables network support)
-a <mask> access mask for UNIX socket, in octal (default: 0700)
-l <ip_addr> interface to listen on (default: INADDR_ANY, all addresses)
-d run as a daemon
-r maximize core file limit
-u <username> assume identity of <username> (only when run as root)
-m <num> max memory to use for items in megabytes (default: 64 MB)
-M return error on memory exhausted (rather than removing items)
-c <num> max simultaneous connections (default: 1024)
-k lock down all paged memory. Note that there is a
limit on how much memory you may lock. Trying to
allocate more than that would fail, so be sure you
set the limit correctly for the user you started
the daemon with (not for -u <username> user;
under sh this is done with 'ulimit -S -l NUM_KB').
-v verbose (print errors/warnings while in event loop)
-vv very verbose (also print client commands/reponses)
-vvv extremely verbose (also print internal state transitions)
-h print this help and exit
-i print memcached and libevent license
-P <file> save PID in <file>, only used with -d option
-f <factor> chunk size growth factor (default: 1.25)
-n <bytes> minimum space allocated for key+value+flags (default: 48)
-L Try to use large memory pages (if available). Increasing
the memory page size could reduce the number of TLB misses
and improve the performance. In order to get large pages
from the OS, memcached will allocate the total item-cache
in one large chunk.
-D <char> Use <char> as the delimiter between key prefixes and IDs.
This is used for per-prefix stats reporting. The default is
":" (colon). If this option is specified, stats collection
is turned on automatically; if not, then it may be turned on
by sending the "stats detail on" command to the server.
-t <num> number of threads to use (default: 4)
-R Maximum number of requests per event, limits the number of
requests process for a given connection to prevent
starvation (default: 20)
-C Disable use of CAS
-b Set the backlog queue limit (default: 1024)
-B Binding protocol - one of ascii, binary, or auto (default)
-I Override the size of each slab page. Adjusts max item size
(default: 1mb, min: 1k, max: 128m)
lindowsmatoMacBook-Pro:~ lindows$telnet 192.168.100.149 11211
Trying 192.168.100.149...
Connected to 192.168.100.149.
Escape character is '^]'.
ERROR
stats
STAT pid 21251
STAT uptime 12550645
STAT time 1320139198
STAT version 1.4.5
STAT pointer_size 64
STAT rusage_user 10126.795493
STAT rusage_system 21859.064917
STAT curr_connections 216
STAT total_connections 5374458
STAT connection_structures 426
STAT cmd_get 684113237
STAT cmd_set 2941276
STAT cmd_flush 0
STAT get_hits 683389325
STAT get_misses 723912
STAT delete_misses 520993
STAT delete_hits 51931
STAT incr_misses 0
STAT incr_hits 0
STAT decr_misses 0
STAT decr_hits 0
STAT cas_misses 0
STAT cas_hits 0
STAT cas_badval 0
STAT auth_cmds 0
STAT auth_errors 0
STAT bytes_read 22365116565
STAT bytes_written 960876073524
STAT limit_maxbytes 3145728000
STAT accepting_conns 1
STAT listen_disabled_num 0
STAT threads 4
STAT conn_yields 0
STAT bytes 313173
STAT curr_items 260
STAT total_items 2941276
STAT evictions 0
STAT reclaimed 467616
END
ERROR
quit
Connection closed by foreign host.
lindowsmatoMacBook-Pro:~ lindows$
memcache充当session server方案
http://netli.iyunv.com/blog/686925
java_memcached-release_2.6.2.zip
https://github.com/gwhalin/Memcached-Java-Client/downloads
http://dl.iyunv.com/topics/download/685c752b-8690-34c5-8783-6d05c9060aab
lindowsmatoMacBook-Pro:java_memcached-release_2.6.2 lindows$ ls -l
total 512
-rwxr-xr-x 1 lindows staff 1814 8 12 09:04 README
-rwxr-xr-x 1 lindows staff 100472 5 25 13:37 commons-pool-1.5.6.jar
-rwxr-xr-x 1 lindows staff 118424 8 12 09:00 java_memcached-release_2.6.2.jar
-rwxr-xr-x 1 lindows staff 25496 5 25 12:35 slf4j-api-1.6.1.jar
-rwxr-xr-x 1 lindows staff 7669 5 25 12:35 slf4j-simple-1.6.1.jar
192.168.121.17
java_memcached-release_2.0.1.jar
# ps -ef | grep memcache
apache 2780 1 0 Jul05 ? 00:01:47 /usr/local/memcached/bin/memcached -d -m 128 -l 127.0.0.1 -p 11211 -u apache
apache 2782 1 0 Jul05 ? 00:00:00 /usr/local/memcached/bin/memcached -d -m 128 -l 127.0.0.1 -p 11210 -u apache
root 14800 1 0 Jul30 ? 00:01:49 java -Xms1024m -Xmx1024m-classpath /home/ecccs/work/LiveChat41/Live_Chat41_Server/Sys_Lib/ant.jar:/home/ecccs/work/LiveChat41/Live_Chat41_Server/Sys_Lib/jdom.jar:/home/ecccs/work/LiveChat41/Live_Chat41_Server/Sys_Lib/classes12.jar:/home/ecccs/work/LiveChat41/Live_Chat41_Server/Sys_Lib/commons-logging-1.0.4.jar:/home/ecccs/work/LiveChat41/Live_Chat41_Server/Sys_Lib/java_memcached-release_2.0.1.jar:/home/ecccs/work/LiveChat41/Live_Chat41_Server/Sys_Lib/log4j-1.2.8.jar:/home/ecccs/work/LiveChat41/Live_Chat41_Server/Sys_Lib/mysql-connector-java-3.1.12-bin.jar:/home/ecccs/work/LiveChat41/Live_Chat41_Server/Sys_Lib/proxool-0.9.0RC3.jar:/home/ecccs/work/LiveChat41/Live_Chat41_Server/ReportForICC/classes-Djava.nio.use_epoll=true business.JReportApp 1
# netstat -atpln | grep 11211
tcp 0 0 127.0.0.1:11211 0.0.0.0:* LISTEN 2780/memcached
tcp 0 0 127.0.0.1:37875 127.0.0.1:11211 TIME_WAIT -
tcp 0 0 127.0.0.1:37879 127.0.0.1:11211 TIME_WAIT -
tcp 0 0 127.0.0.1:37878 127.0.0.1:11211 TIME_WAIT -
tcp 0 0 127.0.0.1:37876 127.0.0.1:11211 TIME_WAIT -
tcp 0 0 127.0.0.1:37121 127.0.0.1:11211 TIME_WAIT -
tcp 0 0 127.0.0.1:37122 127.0.0.1:11211 TIME_WAIT -
tcp 0 0 127.0.0.1:37126 127.0.0.1:11211 TIME_WAIT -
tcp 0 0 127.0.0.1:11211 127.0.0.1:50781 ESTABLISHED 2780/memcached
tcp 0 0 ::ffff:127.0.0.1:50781 ::ffff:127.0.0.1:11211 ESTABLISHED 9671/java
# netstat -an | grep 11211 | wc -l
15
192.168.100.149
# ps -ef | grep memcache
root 10159 9611 0 17:20 pts/1 00:00:00 grep memcache
lindows 21251 1 0 Jun09 ? 06:02:56 /usr/local/bin/memcached -d -u root -m 3000 -l 192.168.100.149 -p 11211
# netstat -an | grep 11211 | wc -l
142
# netstat -atpln | grep 11211 | more
tcp 0 0 192.168.100.149:11211 0.0.0.0:* LISTEN 21251/memcached
tcp 0 0 192.168.100.149:11211 192.168.100.99:38319 ESTABLISHED 21251/memcached
tcp 0 0 192.168.100.149:11211 192.168.119.129:37421 ESTABLISHED 21251/memcached
tcp 0 0 192.168.100.149:11211 192.168.119.129:42541 ESTABLISHED 21251/memcached
tcp 0 0 192.168.100.149:11211 192.168.119.129:37679 ESTABLISHED 21251/memcached
tcp 0 0 192.168.100.149:11211 192.168.119.129:42536 ESTABLISHED 21251/memcached
# ls -l /usr/local/lib
total 4980
lrwxrwxrwx 1 root root 21 Jun 9 10:48 libevent-2.0.so.5 -> libevent-2.0.so.5.1.0
-rwxr-xr-x 1 root root 946708 Jun 9 10:48 libevent-2.0.so.5.1.0
-rw-r--r-- 1 root root 1541136 Jun 9 10:48 libevent.a
lrwxrwxrwx 1 root root 26 Jun 9 10:48 libevent_core-2.0.so.5 -> libevent_core-2.0.so.5.1.0
-rwxr-xr-x 1 root root 555297 Jun 9 10:48 libevent_core-2.0.so.5.1.0
-rw-r--r-- 1 root root 930318 Jun 9 10:48 libevent_core.a
-rwxr-xr-x 1 root root 977 Jun 9 10:48 libevent_core.la
lrwxrwxrwx 1 root root 26 Jun 9 10:48 libevent_core.so -> libevent_core-2.0.so.5.1.0
lrwxrwxrwx 1 root root 27 Jun 9 10:48 libevent_extra-2.0.so.5 -> libevent_extra-2.0.so.5.1.0
-rwxr-xr-x 1 root root 413593 Jun 9 10:48 libevent_extra-2.0.so.5.1.0
-rw-r--r-- 1 root root 610890 Jun 9 10:48 libevent_extra.a
-rwxr-xr-x 1 root root 984 Jun 9 10:48 libevent_extra.la
lrwxrwxrwx 1 root root 27 Jun 9 10:48 libevent_extra.so -> libevent_extra-2.0.so.5.1.0
-rwxr-xr-x 1 root root 942 Jun 9 10:48 libevent.la
lrwxrwxrwx 1 root root 30 Jun 9 10:48 libevent_pthreads-2.0.so.5 -> libevent_pthreads-2.0.so.5.1.0
-rwxr-xr-x 1 root root 18094 Jun 9 10:48 libevent_pthreads-2.0.so.5.1.0
-rw-r--r-- 1 root root 18678 Jun 9 10:48 libevent_pthreads.a
-rwxr-xr-x 1 root root 1005 Jun 9 10:48 libevent_pthreads.la
lrwxrwxrwx 1 root root 30 Jun 9 10:48 libevent_pthreads.so -> libevent_pthreads-2.0.so.5.1.0
lrwxrwxrwx 1 root root 21 Jun 9 10:48 libevent.so -> libevent-2.0.so.5.1.0
drwxr-xr-x 2 root root 4096 Jun 9 10:48 pkgconfig
# ls -l /usr/local/lib/pkgconfig/
total 8
-rw-r--r-- 1 root root 333 Jun 9 10:48 libevent.pc
-rw-r--r-- 1 root root 370 Jun 9 10:48 libevent_pthreads.pc
http://pecl.php.net/package/memcache
http://downloads.php.net/pierre/
http://sunney2010.iyunv.com/blog/656905
http://hi.baidu.com/%D6%B0%B3%A1%D0%C2%CA%D6%B9%FE%B9%FE/blog/item/1765f3d6c7763ad4a144dfda.html
http://www.cnblogs.com/daviyang/archive/2010/04/16/1859385.html
http://hi.baidu.com/baijunhui/blog/item/e395ddd40804b90ca08bb769.html/cmtid/ddde05433540ce1f9213c6cc
http://pecl.php.net/package/memcache
http://www.360doc.com/content/10/1210/15/59865_76785815.shtml
http://www.it118.org/Specials/c1b83237-8710-472c-8ceb-dd3059340f7d/9ff63b86-6629-4a99-8162-84506ccf3c06.htm
http://hi.baidu.com/lzyu/blog/item/05eac813dba80d045baf5364.html
http://hi.baidu.com/%D2%BB%D2%B3%B0%C9/blog/item/1ec6ed79ced80de20bd18759.html
http://hi.baidu.com/baijunhui/blog/item/e395ddd40804b90ca08bb769.html
http://my.oschina.net/wdlinux/blog/8993
http://www.monkey.org/~provos/libevent/
http://www.danga.com/memcached/apis.bml
Java API
A Java API is maintained by Greg Whalinfrom Meetup.com.You can find that library here:
[*]http://www.whalin.com/memcached/-- Java API for memcached
An improved Java API maintained by Dustin Sallings is alsoavailable. Aggressively optimised, ability to run async, supportsbinary protocol, etc. See site for details:
[*]http://bleu.west.spy.net/~dustin/projects/memcached/-- Improved Java API for memcached
http://num7.iyunv.com/blog/212778
Memcache是什么
Memcache是danga.com的一个项目，最早是为 LiveJournal 服务的，目前全世界不少人使用这个缓存项目来构建自己大负载的网站，来分担数据库的压力。
它可以应对任意多个连接，使用非阻塞的网络IO。由于它的工作机制是在内存中开辟一块空间，然后建立一个HashTable，Memcached自管理这些HashTable。
Memcache官方网站：http://www.danga.com/memcached，更多详细的信息可以来这里了解 http://www.ccvita.com/wp-includes/images/smilies/icon_smile.gif
为什么会有Memcache和memcached两种名称？
其实Memcache是这个项目的名称，而memcached是它服务器端的主程序文件名，知道我的意思了把~~~~。一个是项目名称，一个是主程序文件名，在网上看到了很多人不明白，于是混用了。
Memcache的安装
分为两个过程：memcache服务器端的安装和memcached客户端的安装。
所谓服务器端的安装就是在服务器（一般都是linux系统）上安装Memcache实现数据的存储
所谓客户端的安装就是指php（或者其他程序，Memcache还有其他不错的api接口提供）去使用服务器端的Memcache提供的函数，需要php添加扩展。
具体的配置大家可以参考：
Linux下的Memcache安装：http://www.ccvita.com/257.html
Windows下的Memcache安装：http://www.ccvita.com/258.html
Memcache基础教程：http://www.ccvita.com/259.html
Discuz!的Memcache缓存实现：http://www.ccvita.com/261.html
Memcache协议中文版：http://www.ccvita.com/306.html
Memcache的使用和协议分析详解
http://blog.csdn.net/heiyeshuwu/archive/2006/11/13/1380838.aspx
http://baike.baidu.com/view/1193094.htm
Spring+memcache
http://neptune.iyunv.com/blog/220454
MemCached 压力测试
http://www.iyunv.com/topic/77560
命令行查看memcache状态
http://www.51testing.com/?uid-116228-action-viewspace-itemid-107545
memcache的运行状态可以方便的用stats命令显示。
首先用telnet 127.0.0.1 11211这样的命令连接上memcache，然后直接输入stats就可以得到当前memcache的状态。
这些状态的说明如下：
pidmemcache服务器的进程IDuptime服务器已经运行的秒数time服务器当前的unix时间戳versionmemcache版本pointer_size当前操作系统的指针大小（32位系统一般是32bit）rusage_user进程的累计用户时间rusage_system进程的累计系统时间curr_items服务器当前存储的items数量total_items从服务器启动以后存储的items总数量bytes当前服务器存储items占用的字节数curr_connections当前打开着的连接数total_connections从服务器启动以后曾经打开过的连接数connection_structures服务器分配的连接构造数cmd_getget命令（获取）总请求次数cmd_setset命令（保存）总请求次数get_hits总命中次数get_misses总未命中次数evictions为获取空闲内存而删除的items数（分配给memcache的空间用满后需要删除旧的items来得到空间分配给新的items）bytes_read总读取字节数（请求字节数）bytes_written总发送字节数（结果字节数）limit_maxbytes分配给memcache的内存大小（字节）threads当前线程数
memcached安装
http://www.51testing.com/?uid-116228-action-viewspace-itemid-149319
1、 安装文件准备
1）、Memcache的服务器端程序：当前最新版本号为
下载地址：http://www.danga.com/memcached/download.bml
2）、Memcache的安装先决条件：先安装libevent，当前最新版本号为
Libevent介绍：libevent是一个事件触发的网络库，适用于windows、linux、bsd等多种平台，内部使用select、epoll、kqueue等系统调用管理事件机制。著名的用于apache的php缓存库memcached据说也是libevent based，而且libevent在使用上可以做到跨平台，而且根据libevent官方网站上公布的数据统计，似乎也有着非凡的性能。
下载地址：http://monkey.org/~provos/libevent/
2、 操作系统要求
鉴于我们线上环境和线下的要保持一致，我们都将采用linux。具体的版本号为：
Redhat advance server4 v4，可以使用更高版本（更高版本未经测试）
如果是redhat advance server4 v2 ,请保证gcc编译器可以使用，或者升级到v4然后安装gcc编译器。一般升级的方式都是从光盘启动升级过程，升级后安装gcc编译器。默认的v2版本没有安装gcc编译器。
3、 编译器要求
Memcache的安装文件是要求我们安装gcc编译器的。否则我们的libevent和memcache都无法安装。
检查是否有gcc编译器的命令：gcc –v
如果系统的gcc编译器可以用，将会有一段描述，否则提示找不到类库。
成功的例如：
Reading specs from /usr/lib/gcc/i386-redhat-linux/3.4.6/specs
Configuredwith: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --disable-checking --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-java-awt=gtk --host=i386-redhat-linux
Thread model: posix
gcc version 3.4.6 20060404 (Red Hat 3.4.6-3)
4、 安装
先安装libevent，然后才能安装memcache
1）、libevent安装
//先解压缩
#tar -zxvf libevent-1.4.8-stable.tar.gz
//切换到libevent的目录中
#cd libevent-1.4.8-stable
//指定安装路径到/usr/目录下
#./configure --prefix=/usr/
//编译
#make
//安装
#.make install
2）、memcache服务器安装
//先解压缩memcached-1.2.6.tar.gz
#tar -zxvf memcached-1.2.6.tar.gz
//切换到memcache的目录中
#cd memcached-1.2.6
//指定安装路径到/usr/local/server/memcache目录下,同时指定libevent的安装位置
# ./configure --prefix=/usr/local/memcached --with-libevent=/usr/
//编译
#make
//安装
#.make install
测试每步是否安装成功：
测试libevent：
# ls /usr/lib |grep libevent
libevent-1.4.so.2
libevent-1.4.so.2.1.1
libevent.a
libevent.la
libevent.so
libevent_core-1.4.so.2
libevent_core-1.4.so.2.1.1
libevent_core.a
libevent_core.la
libevent_core.so
libevent_extra-1.4.so.2
libevent_extra-1.4.so.2.1.1
libevent_extra.a
libevent_extra.la
libevent_extra.so
测试memcache：
# ls -al /usr/local/memcached/bin
total 264
drwxr-xr-x 2 root root 4096 Sep 19 15:31 .
drwxr-xr-x 4 root root 4096 Sep 19 15:31 ..
-rwxr-xr-x 1 root root 120949 Sep 19 15:31 memcached
-rwxr-xr-x 1 root root 129947 Sep 19 15:31 memcached-debug
5、 启动memcache
1）、启动Memcache的服务器端：
# /usr/local/bin/memcached -d -m 100 -u root -l 192.168.36.200 -p 11211 -c 256 -P /tmp/memcached.pid
# /usr/local/bin/memcached -d -m 10 -u root -l 192.168.0.200 -p 12000 -c 256 -P /tmp/memcached.pid
-d选项是启动一个守护进程，
-m是分配给Memcache使用的内存数量，单位是MB，我这里是100MB，
-u是运行Memcache的用户，我这里是root，
-l是监听的服务器IP地址，如果有多个地址的话，我这里指定了服务器的IP地址192.168.36.200，
-p是设置Memcache监听的端口，我这里设置了11211，最好是1024以上的端口，我们这里统一使用11211
-c选项是最大运行的并发连接数，默认是1024，我这里设置了256，按照你服务器的负载量来设定。
-P是设置保存Memcache的pid文件，我这里是保存在/tmp/memcached.pid，
2）、如果要结束Memcache进程，执行：
# kill cat /tmp/memcached.pid
6、 监测是否启动成功方式
我们可以使用telnet来对我们的memcache服务器进行访问
例如：telnet 192.168.36.199 11211 （访问的是192.168.36.199这个ip的11211端口）
连接上后，直接敲击stats命令看当前缓存服务器状态
7、 设定memcache的telnet访问限制
请限定telnet的访问，使之只能在中转机上访问
8、 memcache的常见概念
memcached会预先分配内存，memcached分配内存方式称之为allocator，首先，这里有3个概念：
1 slab
2 page
3 chunk
解释一下，一般来说一个memcahced进程会预先将自己划分为若干个slab，每个slab下又有若干个page，每个page下又有多个chunk，如果我们把这3个咚咚看作是object得话，这是两个一对多得关系。再一般来说，slab得数量是有限得，几个，十几个，或者几十个，这个跟进程配置得内存有关。而每个slab下得page默认情况是1m，也就是说如果一个slab占用100m得内存得话，那么默认情况下这个slab所拥有得page得个数就是100，而chunk就是我们得数据存放得最终地方。
9、 Memcache的常用命令
Memcache常见的命令都在协议文件上：安装文件的的doc目录下的protocol.txt文件中有详细说明
1）、查询状态命令：stats:
Name Type Meaning
----------------------------------
pid 32u Process id of this server process
uptime 32u Number of seconds this server has been running
time 32u current UNIX time according to the server
version string Version string of this server
pointer_size 32 Default size of pointers on the host OS
(generally 32 or 64)
rusage_user 32u:32u Accumulated user time for this process
(seconds:microseconds)
rusage_system 32u:32u Accumulated system time for this process
(seconds:microseconds)
curr_items 32u Current number of items stored by the server
total_items 32u Total number of items stored by this server
ever since it started
bytes 64u Current number of bytes used by this server
to store items
curr_connections 32u Number of open connections
total_connections 32u Total number of connections opened since
the server started running
connection_structures 32u Number of connection structures allocated
by the server
cmd_get 64u Cumulative number of retrieval requests
cmd_set 64u Cumulative number of storage requests
get_hits 64u Number of keys that have been requested and
found present
get_misses 64u Number of items that have been requested
and not found
evictions 64u Number of valid items removed from cache
to free memory for new items
bytes_read 64u Total number of bytes read by this server
from network
bytes_written 64u Total number of bytes sent by this server to
network
limit_maxbytes 32u Number of bytes this server is allowed to
use for storage.
threads 32u Number of worker threads requested.
(see doc/threads.txt)
2）、查询版本号 version
3）、退出命令 quit
4）、显示各个slab的信息，包括chunk的大小、数目、使用情况等：stats slabs5）、显示各个slab中item的数目和最老item的年龄(最后一次访问距离现在的秒数)：stats items
6）、显示内存分配：stats malloc
7）、清空缓存数据（其实是将所有缓存数据标记为过期）：flush_all
end
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