Memcached Session Provider

This is a highly available, high performance ASP.NET session state store provider using Memcached.

Features:

Handles Memcached node failures
No session locking per request

Handling node failures

In a pool of memcached nodes, sessions are distributed equally across all the nodes. Additionally, for every session, a backup copy is stored on a secondary memcached node. This is similar to the way Memcached session manager for Tomcat is implemented.

Example: In a pool of 2 memcached nodes, if a session S1 gets stored on memcached node M1, the backup session bak:S1 is stored on node M2. If node M1 goes down, session is not lost. It will be retrived from the M2 node without any interruption. Similarly, M1 acts as backup node for M2, in case M2 goes down.

<M1>     <M2>
 S1		  S2
bak:S2	 bak:S1

Note that if only 1 memcached node is configured then there is no backup.

No session locking

Session locking in ASP.NET can cause a few performance problems. This custom implementation of Session provider does not lock any Session. This should not be a problem in most cases. But if you need locked, consistent data as part of the session, you can implement a lock/concurrency check in your application, or use a different Memcached provider (see here and here).

Requirements

You'll need .NET Framework 3.5 or later to use the precompiled binaries. To build client, you'll need Visual Studio 2012.

Install

In your web project, include the assembly via NuGet Package.

Web.config

This library uses the Enyim Memcached client. Make the following changes in the web.config file for Enyim client

<configuration>
	<configSections>
		<sectionGroup name="sessionManagement">
			<section name="memcached" type="Enyim.Caching.Configuration.MemcachedClientSection, Enyim.Caching" />
		</sectionGroup>
	</configSections>

	<sessionManagement>
		<memcached protocol="Binary">
			<servers>
				<!-- make sure you use the same ordering of nodes in every configuration you have -->
				<add address="ip address" port="port number" />
				<add address="ip address" port="port number" />
			</servers>
			<locator type="MemcachedSessionProvider.SessionNodeLocator, MemcachedSessionProvider" />
		</memcached>
	</enyim.com>

</configuration>

memcached/locator

The memcached/locator is used to map objects to servers in the pool. Replace the default implementation with the type MemcachedSessionProvider.SessionNodeLocator, MemcachedSessionProvider. This handles the session backup.

See here for more configuration options for Enyim Memcached

Also make the following change in web.config to use the custom Session State provider

<configuration>

	<system.web>
		
		<sessionState customProvider="Memcached" mode="Custom">
			<providers>
				<add name="Memcached" type="MemcachedSessionProvider.SessionProvider, MemcachedSessionProvider" />
			</providers>
		</sessionState>

	</system.web>

</configuration>

Questions?

If you have questions, bugs reports, or feature requests, please submit them via the Issue Tracker.

Reference

This implementation is based on the sample provided by Microsoft.

henkmeulekamp / MemcachedSessionProvider