Memcached (Distributed Cache) ASP.net Provider

• http://www.codeplex.com/memcachedproviders

Introduction

Currently I am working on a web-based project that will be hosted in a web farm. Among the several issues, we faced the issue of having a distributed cache. As we know the current cache in ASP.net is an in-process cache and can't be used in a web farm. After doing some research found a few solutions on the web but at the end all of them had scalability issues. We found a few third party implementations but they were quite expensive. Then I came across memcahced implemented by Danga Interactive. This is a high performance distributed memory cache initially implemented for http://www.LiveJournal.com. The original implementation runs on *nix system. Luckily there is win32 port available at http://jehiah.cz/projects/memcached-win32/ for those who want to run it in a windows environment. For more detail on the working of Memcached, please read the following article http://www.linuxjournal.com/article/7451.

There is a C# client for memcached available and can be downloaded from the following location https://sourceforge.net/projects/memcacheddotnet/. For coding this provider, I have used the clientlib 1.1.5.

Using the code

Following is the interface for the Cached Provider.

public abstract class CacheProvider : ProviderBase
 {
    // Currently returns -1 as this property is not implemented
    public abstract long Count { get;}
    // Returns the server names with port in the memcached cluster
    public abstract string[] Servers { get;}
    // Default expiration time in milli seconds
    public abstract long DefaultExpireTime { get;set;}
    // Adds object to the cache for the max amount of time
    public abstract bool Add(string strKey, object objValue);
    // Adds object to the cache for Default Expire time if bDefaultExpire
    // is set to true otherwise for max amount of time
    public abstract bool Add(string strKey, object objValue,bool bDefaultExpire);
    // Add objects for specified about of time. Time is specified in milli seconds        
    public abstract bool Add(string strKey, object objValue, long lNumofMilliSeconds);
    // Return the object from memcached based on the key otherwise 
    // just returns null
    public abstract object Get(string strKey);
    // Clears everything from the cache on all servers
    public abstract bool RemoveAll();
    // Removes the an object from cache
    public abstract object Remove(string strKey);
    // Release resources and performs clean up
    public abstract void Shutdown();
    // Checks if the key exists in memory
    public abstract bool KeyExists(string strKey);
    // Return all servers stats
    public abstract Hashtable GetStats();
  }

Following is how to configure Cache Provider in a web.config or app.config file

<?xml version="1.0" encoding="utf-8" ?>
<configuration>

 <configSections>
  <section name="cacheProvider" type="CacheProvider.CacheProviderSection, CacheProvider"
             allowDefinition="MachineToApplication" restartOnExternalChanges="true"/>
 </configSections>

 <cacheProvider defaultProvider="MemcachedCacheProvider">
  <providers>
   <add name="MemcachedCacheProvider" type="CacheProvider.MemcachedCacheProvider,CacheProvider"
   servers="127.0.0.1:11211" socketConnectTimeout="1000" socketTimeout="1000"/>

   <!�To add more servers use comma to separate servernames and ports
   eg. servers="127.0.0.1:11211,192.168.0.111:11211"
   -->

  </providers> 
 </cacheProvider>
</configuration>

Following parameters can be specified for initializing the cache provider

• socketConnectTimeout � Timeout for Socket connection with memcached servers
• socketTimeout � Timeout for Socket read-write operations
• defaultExpireTime � Default expire time in milliseconds

To use Cache Provider in a project add a reference to the CacheProvider.dll and access the methods using DistCache static class. When creating keys for storing data, avoid using spaces in keys e.g. "My Key". This is an issue with C# memcached client. To close the provider gracefully please add a call to DistCache.Shutdown() in Global.asax file's Application_End event.

Update Dec 24, 2007
To report any issues and enhancements please go to the following link http://www.codeplex.com/memcachedproviders. I have started working on the Session State Provider for Memcached. I will be releasing it very soon on codeplex.com.

Update Dec 31, 2007I have released Session State Provider for memcached. Please go to the following link to download
http://www.codeplex.com/memcachedproviders

References

1. http://www.danga.com/memcached/
2. http://jehiah.cz/projects/memcached-win32/
3. https://sourceforge.net/project/showfiles.php?group_id=152153
4. Sample Project Provider by Memcached C# client 1.1.5
5. http://www.infoq.com/news/2007/07/memcached
6. http://msdn2.microsoft.com/en-US/library/aa479038.aspx
7. http://www.linuxjournal.com/article/7451