How to install and configure memcached

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7

Issue

  • How to install memcached.
  • How to configure memcached.
  • How to start and stop memcached.
  • How to capture memcached logs in /var/log/memcached.
  • How to see memcached slabs and stats.
  • High CPU utilization on memcached servers.

Resolution

What is Memcached.

Memcached is an open source, high-performance, distributed memory object caching system. While it is generic in nature, it is intended for use in speeding up dynamic web applications by alleviating database load.

Memcached is an in-memory key-value store for small chunks of arbitrary data (strings, objects) from results of database calls, API calls, or page rendering.

Memcached allows applications to take memory from parts of system where it has more than it needs and make it accessible to areas where applications have less than they need.

How to install memcached.

rhel-6-server-rpms repository from Red Hat:

# yum install memcached

How to configure memcached.

Configure a firewall

First and foremost, set up a firewall in your LAN if memcached servers should be accessible only from within your local network. Do not allow external traffic to ports used by memcached (e.g. 11211 as used by default).

Disable UDP

If you are not required to use UDP for memcached, we highly recomment switching to TCP connections for your memcached server (add "-U 0" to the OPTIONS variable in /etc/sysconfig/memcached). If you do require the use of UDP and require remote access to memcached servers (for example, in a clustering scenario), it is recommended to configure a firewall to allow connections only from trusted hosts.

Configure memcached

To configure memcached, edit the file /etc/sysconfig/memcached as follows

# vi /etc/sysconfig/memcached

Change the values as shown below and add the IP address of your server on which memcached is installed.

PORT="11211"
USER="memcached"
# max connection 2048
MAXCONN="2048"
# set ram size to 2048 - 2GiB
CACHESIZE="4096"
# disable UDP and listen to loopback ip 127.0.0.1, for network connection use real ip e.g., 10.0.0.5
OPTIONS="-U 0 -l 127.0.0.1"

How to configure your logs to /var/log/memcached.

To configure logs

In order to capture memcached logs, configure /etc/sysconfig/memcached as follows:

OPTIONS="-vv >> /var/log/memcached 2>&1"

Start memcached

Start or Stop memcached

After the above configurations, it is time to start the memcached service as below:

# chkconfig memcached on
# service memcached start

In order to stop/restart memcached, run the following commands:

# service memcached stop
# service memcached restart

Root Cause

  • High resource utilization can happen due to low configurations settings for maximum connections and cachesize.
    Increase the value of "maxconn" and "cachesize"
# cat /etc/sysconfig/memcached*
PORT="11211"
USER="memcached"
# max connection 2048
MAXCONN="2048"
# set ram size to 4096 - 4GiB
CACHESIZE="4096"

Diagnostic Steps

How to use memcached-tool to verify slabs and stats.

To check and verify memcached slabs

# memcached-tool IP_ADDRESS:Port
# memcached-tool IP_ADDRESS:Port display
# memcached-tool 127.0.0.1:11211
# memcached-tool 127.0.0.1:11211 display

Sample output.

#  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

Verify memcached stats

In order to verify memcached statics, run the following commands:

# memcached-tool IP_Address:Port stats
# memcached-tool 127.0.0.1:11211 stats

Sample output from above command:

#127.0.0.1:11211   Field       Value
accepting_conns           1
               auth_cmds           0
             auth_errors           0
                   bytes           0
              bytes_read          87
           bytes_written        3205
              cas_badval           0
                cas_hits           0
              cas_misses           0
               cmd_flush           0
                 cmd_get           0
                 cmd_set           0
             conn_yields           0
   connection_structures          11
        curr_connections          10
              curr_items           0
               decr_hits           0
             decr_misses           0
             delete_hits           0
           delete_misses           0
               evictions           0
                get_hits           0
              get_misses           0
               incr_hits           0
             incr_misses           0
          limit_maxbytes  4294967296
     listen_disabled_num           0
                     pid        7679
            pointer_size          64
           rusage_system    0.030995
             rusage_user    0.048992
                 threads           4
                    time  1407726751
       total_connections          17
             total_items           0
                  uptime        4999
                 version       1.4.4

References:

  1. Memcached Project

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