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How do I install memcached a high-performance, distributed memory object caching system, generic in nature, but intended for use in speeding up dynamic web applications by alleviating database load under CentOS / RHEL / Fedora / Redhat Linux?

Memcached is very fast caching system for MySQL. It uses libevent or epoll (Linux runtime) to scale to any number of open connections and uses non-blocking network I/O.

Required Packages

1. memcached : High Performance, Distributed Memory Object Cache.
2. memcached-selinux : SELinux policy module supporting memcached.
3. perl-Cache-Memcached : Perl client for memcached.
4. php-pecl-memcache : Php client / extension to work with the Memcached caching daemon.
5. python-memcached : A Python memcached client library.

Step # 1: Turn on EPEL Repo

Type the following command to enable EPEL repo which carries required memcache packages.
rpm -Uvh http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarch.rpm
See this FAQ for further details.

Step # 2: Install memcached

Type the following command to install memcached with php extension:
# yum install memcached php-pecl-memcache memcached-selinux
Sample outputs:

Loaded plugins: downloadonly, rhnplugin, security, verify
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package memcached.x86_64 0:1.2.8-1.el5 set to be updated
--> Finished Dependency Resolution

Dependencies Resolved

==============================================================================================================================================================
Package                                Arch                                Version                                   Repository                         Size
==============================================================================================================================================================
Installing:
memcached                              x86_64                              1.2.8-1.el5                               epel                               60 k

Transaction Summary
==============================================================================================================================================================
Install      1 Package(s)
Update       0 Package(s)
Remove       0 Package(s)        

Total download size: 60 k
Is this ok [y/N]: y
Downloading Packages:
memcached-1.2.8-1.el5.x86_64.rpm                                                                                                       |  60 kB     00:00
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
 Installing     : memcached                                                                                                                              1/1

Installed:
 memcached.x86_64 0:1.2.8-1.el5                                                                                                                             

Complete!

Step # 3: Configure memcached

Edit /etc/sysconfig/memcached, enter:
# vi /etc/sysconfig/memcached
Update it as follows:

PORT="11211"
USER="memcached"
# max connection 2048
MAXCONN="2048"
# set ram size to 2048 - 2GiB
CACHESIZE="4096"
# listen to loopback ip 127.0.0.1, for network connection use real ip e.g., 10.0.0.4
OPTIONS="-l 127.0.0.1"

The above will starts memcached up as a daemon, using 4GB of memory, and listening on IP 127.0.0.1, port 11211. Save and close the file.

Step # 4: Run memcached

Type the following command to start memcached, enter:
# chkconfig memcached on
# service memcached start
To stop / restart use the following commands:
# service memcached stop
# service memcached restart

How Do I See Memory Memcached Slabs?

Type the following command:
# memcached-tool IP_ADDRESS:Port
# memcached-tool IP_ADDRESS:Port display
# memcached-tool 127.0.0.1:11211
Sample outputs:

  #  Item_Size   Max_age  1MB_pages Count   Full?
 1     104 B     5134 s       1      10      no
 2     136 B     5135 s       1      40      no
 3     176 B        0 s       1       0      no
 4     224 B     2648 s       1       7      no
 8     552 B     1810 s       1      12      no
 9     696 B     1810 s       1       6      no
10     872 B     2935 s       1       8      no
11     1.1 kB    4262 s       1      18      no
12     1.3 kB    2990 s       1      23      no
13     1.7 kB    2434 s       1      22      no
14     2.1 kB    3489 s       1      11      no
15     2.6 kB    2964 s       1      16      no
16     3.3 kB    2861 s       1      14      no
17     4.1 kB    2076 s       1       5      no
18     5.2 kB    2981 s       1       5      no
20     8.1 kB      64 s       1       1      no
21    10.1 kB    1865 s       1       3      no
29    60.2 kB    1550 s       1       2      no

How Do I See Memory Memcached Stats?

Type the following command:
# memcached-tool IP_Address:Port stats
# memcached-tool 127.0.0.1:11211 stats
Sample outputs:

#127.0.0.1:11211   Field       Value
        accepting_conns           1
                  bytes      399395
             bytes_read      504797
          bytes_written    17313658
              cmd_flush           0
                cmd_get        1141
                cmd_set         248
  connection_structures           9
       curr_connections           5
             curr_items         205
              evictions           0
               get_hits         898
             get_misses         243
         limit_maxbytes  1073741824
    listen_disabled_num           0
                    pid       40159
           pointer_size          64
          rusage_system    0.227965
            rusage_user    0.034994
                threads           5
                   time  1255803547
      total_connections         344
            total_items         259
                 uptime        5829
                version       1.2.8

Further readings:

• Memcached project