memcached

memcached

Synopsis #

memcached is a high-performance in-memory key-value store used primarily for caching data to reduce database load and latency in dynamic web applications. It provides a simple TCP protocol for setting and retrieving short-lived values and is often used by frameworks like Django, Rails, and PHP.

memcached is available on OpenBSD via packages and integrates with rcctl(8) for service management.

Unlike Redis, memcached is not persistent and supports only very simple key-value operations.

Installation #

Install memcached using the package system:

# pkg_add memcached

This installs:

  • /usr/local/bin/memcached — the daemon
  • /etc/rc.d/memcached — rcctl control script

Configuration #

memcached is typically configured via command-line options. These options can be set persistently by editing the rcctl flags:

# rcctl set memcached flags "-m 64 -l 127.0.0.1 -p 11211"

Common options:

  • -m 64 — allocate 64 MB of RAM
  • -l 127.0.0.1 — bind only to localhost
  • -p 11211 — default TCP port

To apply changes:

# rcctl enable memcached
# rcctl start memcached

Testing Basic Usage #

Use the telnet(1) client to test memcached:

$ telnet localhost 11211
Trying 127.0.0.1...
Connected to localhost.
set testkey 0 300 5
hello
STORED
get testkey
VALUE testkey 0 5
hello
END
  • set <key> <flags> <ttl> <bytes>
  • get <key>

Keys expire after the specified TTL in seconds.

To quit:

quit

Using with Clients #

memcached is supported by many programming languages. Examples:

  • PHP: memcached or memcache extension
  • Python: python3-memcached or pymemcache
  • Ruby: dalli gem

Example Python usage:

import memcache
mc = memcache.Client(['127.0.0.1:11211'])
mc.set('greeting', 'hello', time=300)
print(mc.get('greeting'))

Security Considerations #

memcached does not support authentication or TLS. It must be run on trusted networks only.

By default, it should be bound to 127.0.0.1. If remote access is necessary:

  1. Adjust flags:
# rcctl set memcached flags "-m 128 -l 192.0.2.1 -p 11211"
  1. Restrict access using pf(4):
pass in on $int_if proto tcp from 192.0.2.0/24 to port 11211
block in on $int_if proto tcp from any to port 11211
  1. Reload pf and restart memcached:
# pfctl -f /etc/pf.conf
# rcctl restart memcached

Never expose memcached to the public Internet.

Service Management #

To start and enable at boot:

# rcctl enable memcached
# rcctl start memcached

To stop or restart:

# rcctl stop memcached
# rcctl restart memcached

Check status:

# rcctl check memcached

Logging #

memcached logs to syslog. View logs with:

# tail -f /var/log/daemon

To increase verbosity, add -v or -vv to flags:

# rcctl set memcached flags "-m 64 -v"
# rcctl restart memcached