Webfarm and a static cache (Asp.net)

Evil Phil

Given the below code, which stores key (GUID), value(String) pairs is static it only resides in one place in memory if I'm not mistaken. My question is how will this behave in a webfarm? I'd imagine there would be one static cache per webserver but I don't know how to test it to see exactly what happens.

p.s. The code below is for illustration purposes only and is incomplete as a solution

public static class ValueCache
{
	// Acts as the cache
	private static Dictionary<Guid, String> cache = new Dictionary<Guid, String>();

	/// <summary>
	/// Returns the cached String for a given GUID. 
	/// </summary>
	internal static String getCache(Guid ID)
	{
		if (cache.ContainsKey(ID))
		{
			return cache[ID];
		}
		return null;
	}

	/// <summary>
	/// Adds a String to the cache for a given GUID.
	/// </summary>
	internal static void AddToCache(Guid ID, String value)
	{
		cache[ID] = value;
	}

	/// <summary>
	/// Clears the cache of all objects.
	/// </summary>
	internal static void ClearCache()
	{
		cache.Clear();
	}
}

aidan_walsh

If you're looking to keep a consistant cache across machines in the farm, it might be an idea to look at a solution like memcached.

Evil Phil

I'll have a look at that aidan but I don't thinks a goer for this particular problem.

Anyway, I've scribbled this out on my jotter:

If ServerA has a string value in its static cache (above) and the next request goes to ServerB that won't have value in its static cache will it? If that's the case then static cache solution won't work either.

I don't think it will work with unique values which is what I'm caching. If the values weren't unique, like FieldInfo objects which is what I was originally using, then it would work. Oh well ...

Ginger

You need to change the session state management from InProcess to SQL server when you go beyond one server.

http://msdn2.microsoft.com/en-us/library/h6bb9cz9(VS.71).aspx

Or use Dependency ideas to make sure that your Static Cache is synced

Have a look at this article

http://www.eggheadcafe.com/articles/20030420.asp

I usually use the sessionState element when dealing with web farms for any session management i have dealt with.

Evil Phil

Yeah, I'm going to do the same. Leave the session state management up to developers using the control seems to be the best solution.

Ginger

You can always enable Sticky IPs on the NLB but to be honest, not a bad idea to implement the SQL Server or State server ideas

Eoin

Ginger wrote: »

You need to change the session state management from InProcess to SQL server when you go beyond one server.

I posted a topic here a while ago, about losing session state across two webservers. Our router was supposed to stick a session to a server, but we never got it working. I went with the SQL state server, and it solved all the problems.