Running memcached on Windows

Memcached is a giant distributed hash table, allowing you to cache data in-memory across multiple machines in your data centre. Commonly, in the web 2.0 world, it's used to store the results of frequently-run queries to avoid hitting the database. This allows the database to scale much further, as it moves much of the load into the fast and almost transparent cache, allowing the database to concentrate on write operations. Many users of memcached report (when implemented correctly) database load dropping by a factor of 10 after implementing query caching in memcached.

Running memcached on Windows

Why? Linux is normally the OS of choice for running memcached, due to its stability, performance, and low TCO - I'd never recommend to run memcached on Windows in a production environment. However, the memcached network protocol is the same regardless of the client or server OS, meaning that organisations that develop mainly on the Microsoft platform can use a Linux cluster in production, but still conveniently run memcached on the local Windows development server.

Downloading the memcached server and client

Memcached is available from Danga (of LiveJournal fame) here. Memcached server for Windows is available here, and you can grab the latest .NET client from SourceForge here.

First Look

Unless you get the source release, the downloaded zip file contains a single file, memcached.exe – no documentation, no release notes. If you run this exe with the “–h” option you get the following list of options.

C:\memcached>memcached.exe -h
memcached 1.2.6
-p       TCP port number to listen on (default: 11211)
-U       UDP port number to listen on (default: 0, off)
-s      unix socket path to listen on (disables network support)
-a      access mask for unix socket, in octal (default 0700)
-l   interface to listen on, default is INDRR_ANY
-d start          tell memcached to start
-d restart        tell running memcached to do a graceful restart
-d stop|shutdown  tell running memcached to shutdown
-d install        install memcached service
-d uninstall      uninstall memcached service
-r            maximize core file limit
-u  assume identity of  (only when run as root)
-m       max memory to use for items in megabytes, default is 64 MB
-M            return error on memory exhausted (rather than removing items)
-c       max simultaneous connections, default is 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  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)
-h            print this help and exit
-i            print memcached and libevent license
-b            run a managed instanced (mnemonic: buckets)
-P      save PID in , only used with -d option
-f    chunk size growth factor, default 1.25
-n     minimum space allocated for key+value+flags, default 48

Running the server

Memcached has no configuration file – it's controlled purely by the command line parameters above. To run the server with default settings – 64Mb cache memory, and listening on port 11211.

If you use the “-vv” flag, you get a much more verbose output with details of client connections: Your memcached server is now running.

Running memcached as a Windows Service

The Win32 port also allows you to install and run memcached as a service, using the “-d” (daemonizer) switch with its various options. To install it, run the command:

memcached.exe –d install

This will install the server as a service available in the control panel. To start it, either run the command:

memcached.exe –d start

… or start it from your Services manager:

Configuration

The two main settings that may require configuration are the cache size, and port.

The default cache size is 64mb, which for any web 2.0 application is a pretty paltry cache. You can change the cache size (in megabytes) using the "-m" switch:

memcached.exe –m 1024

The above will configure memcached to use a gigabyte of memory.

Drawbacks to running as a service

If you configure memcached to run as a Windows service, you (as of release 1.2.6) lose the ability to configure the sevice as you would via the command line. The size of the cache defaults to 64mb, and the port to 11211. Parameters supplied on the command line when using “-d start” are ignored.