Memcached is a general-purpose distributed memory caching system. It is often used to speed up dynamic database-driven websites by caching data and objects in RAM to reduce the number of times an external data source (such as a database or API) must be read.
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Nearly every popular CMS has a plugin or module to take advantage of memcached, and many programming languages have a memcached library, including PHP, Perl, Ruby, and Python. Memcached runs in memory and is thus quite speedy, since it does not need to write data to disk.
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We can install Memcached by running this command:

Use the following command to edit the default configuration file /etc/memcached.conf:

You will see default configurations of memcached, such as default port (11211), cap of memory for memcached in megabytes (64) and so on.
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Most common variables to edit:
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​p - port in which memcached is running
​m - cap of memory for memcached
​c - value of maximum connections
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An example how should look configuration file if we want memcached to run on port 12345, to use 2 GB of RAM and have 1024 allowed maximum connections:
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​# memcached default config file
# 2003 - Jay Bonci
# This configuration file is read by the start-memcached script provided as
# part of the Debian GNU/Linux distribution.
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# Run memcached as a daemon. This command is implied, and is not needed for the
# daemon to run. See the README.Debian that comes with this package for more
# information.
-d
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# Log memcached's output to /var/log/memcached
logfile /var/log/memcached.log
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# Be verbose
# -v
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# Be even more verbose (print client commands as well)
# -vv
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# Start with a cap of 64 megs of memory. It's reasonable, and the daemon default
# Note that the daemon will grow to this size, but does not start out holding this much
# memory
​-m 2048
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# Default connection port is 11211
​-p 11211
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# Run the daemon as root. The start-memcached will default to running as root if no
# -u command is present in this config file
-u memcache
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# Specify which IP address to listen on. The default is to listen on all IP addresses
# This parameter is one of the only security measures that memcached has, so make sure
# it's listening on a firewalled interface.
-l 127.0.0.1
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# Limit the number of simultaneous incoming connections. The daemon default is 1024
​ -c 1024
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# Lock down all paged memory. Consult with the README and homepage before you do this
# -k
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# Return error when memory is exhausted (rather than removing items)
# -M
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# Maximize core file limit
# -r

After we had configured mamached to work with the parameters we want, we can start it:

We can test if it is working with commands

or

That's it! You had installed and configured the basics of memcached. So, now you have a very useful program that can significantly improve the server's efficiency.