AppFabric Caching

I have been given a task to research and find out any replacement for ASP.NET Cache. And, whether the cache can be used in any other application type besides web. I have done some research and comparison in AppFabric Caching, Enterprise Library Caching Application Block and System.Runtime.Caching. Today topic cover about AppFabric Caching, next post will cover about System.Runtime.Caching.

Scenario

Normally we are puzzled with which caching technology should we use and what are the differences between AppFabric cache compare to the other cache technology.

The caching feature that AppFabric provided is distributed cache, which mean it makes the cache available and accessible in one or many servers but they are unified into one entity for your application. When you are using ASP.NET cache or any caching facility, you notice that the cache is only available to your own application domain.

Image credit &source from : MSDN

Features

Comparing AppFabric cache vs ASP.NET cache, here are the differences and special features.

1. The cache can be distributed hosting in one or multiple server.
2. The cache can be hosted in a different standalone server, separate from Application server.
3. The cache cluster promote high availability. If one of the cache server is down for some reason, the cache will still be available.
4. The cache automatically sync data between cache hosts.

Configuration

After you have installed and start configuring the AppFabric, you would come across the following window in the wizard.

There are 2 Caching Service configuration provider, one is SQL Server and another is XML. If you wonder which provider to pick, it is depending on your environment. For my server, it is not joined with Active Directory (AD). Therefore, XML is my only option. If you forcefully pick SQL Server, you would get the following notification:

The provider difference is just the location of keeping cache cluster configuration. All the information that you enter in the "Next" page will be stored in SQL Server or a XML file.

Since I am using XML configuration provider, I have to create a new workgroup account to run the Caching Service. You are not allowed to use built-in account such as NT AUTHORITY\NETWORK SERVICE. The same workgroup account needs to be created in the other cache server, and applying same configuration.

Now, you need to pick one of your cache server to be a lead host, then create a network shared folder in that server. The network shared folder must be accessible by other hosts and giving the Cache Service account read/write privilege.

Once you are done with it, configure the File Share in AppFabric Configuration Wizard. Then, set the cluster size. If you are configuring the lead host, choose the New Cluster. For other cache host, choose the Join Cluster.

Next, the default TCP ports which will be used by AppFabric Cache Service are shown in the spinner box. Note them down and create firewall rule to unblock those ports. If you find any of these ports conflicting or is being used by any of you applicantion, you can change the port here.

That's it for AppFabric Cache configuration.

Usage

The cache usage is similar to ASP.NET cache. Open up Visual Studio, create any new project, then add the following assemblies.

C:\Program Files\AppFabric 1.1 for Windows Server\Microsoft.ApplicationServer.Caching.Core.dll

C:\Program Files\AppFabric 1.1 for Windows Server\Microsoft.ApplicationServer.Caching.Client.dll

Note: You need to manually browse and locate the above assemblies. If you add the references from the Assemblies Extension page, they are actually coming from Windows Azure SDK.

The following is the error that you will encounter if you added wrong assemblies:

ErrorCode<ERRCA0019>:SubStatus<ES0001>:Check the client version. It should be within the allowed version range on the server. If necessary, upgrade the client to the allowed version.

The following code need to be run once only to initialize the cache for your application:
Code credit to Scott Hanselman.

private static DataCacheFactory _factory = null;

private static DataCache _cache = null;

public static DataCache GetCache()

{

    if (_cache != null)

        return _cache;

    //List cache host server

    //Note: 22233 is the cache port

    List<DataCacheServerEndpoint> servers = new List<DataCacheServerEndpoint>();

    servers.Add(new DataCacheServerEndpoint("MY-SYLVESTER-01", 22233));

    servers.Add(new DataCacheServerEndpoint("MY-SYLVESTER-02", 22233));

    servers.Add(new DataCacheServerEndpoint("MY-SYLVESTER-03", 22233));

    servers.Add(new DataCacheServerEndpoint("MY-SYLVESTER-04", 22233));

    servers.Add(new DataCacheServerEndpoint("MY-SYLVESTER-05", 22233));

    //Set the cache hosts

    DataCacheFactoryConfiguration configuration = new DataCacheFactoryConfiguration();

    configuration.Servers = servers;

    configuration.LocalCacheProperties = new DataCacheLocalCacheProperties();

    //Set this if you want to get notified if any changes to your cache

    configuration.NotificationProperties = new DataCacheNotificationProperties(10000, new System.TimeSpan(0, 0, 3));

    //Default value for queue length: 10000

    //Default value for poll interval: 300 seconds

    //Disable tracing to avoid informational/verbose messages on the web page

    DataCacheClientLogManager.ChangeLogLevel(System.Diagnostics.TraceLevel.Off);

    //Pass configuration settings to cacheFactory constructor

    _factory = new DataCacheFactory(configuration);

    //Get reference to named cache called "default"

    _cache = _factory.GetCache("default");

    return _cache;

}

In order to insert data into the cache, just the following one liner:

public void SetData(string key, object data)

{

    _cache.Put(key, data);

}

In order to get the data from the cache, one liner as follow:

public object GetData(string key)

{

    return _cache.Get(key);

}

There are more complicated DataCache methods supported, check it out from MSDN.

Cache Notification

If you need the AppFabric Cache Service to notify you any changes to the cache, there are a few callback event can be subscribed. Before you can use this feature, you need to enable it during the cache initialization by setting the DataCacheNotificationProperties in DataCacheFactoryConfiguration.

Also, you need to enable notification by using this PowerShell command: 

Set-CacheConfig -CacheName <Cache Name> -NotificationsEnabled true

You also can change the AppFabric Cache configuration XML file in the shared folder.

Then, restart the cache cluster by restarting the AppFabric Caching Service windows service or executing the PowerShell command: Restart-CacheCluster

All the AppFabric Caching PowerShell command can be found HERE.

Now, I want to get notified when someone replace one of the cache item. The following is the code use to subscribe the callback method:

private static DataCache _cache;

       

static AppFabricCacheService ()

{

    _cache = CacheUtil.GetCache();

    _cache.AddItemLevelCallback(

        "myItem",

        DataCacheOperations.ReplaceItem,

        OnDataCacheItemChanged);

}

private static void OnDataCacheItemChanged(string cacheName, string regionName, string key, DataCacheItemVersion version, DataCacheOperations cacheOperation, DataCacheNotificationDescriptor nd)

{

    Debug.WriteLine("Someone changed my cache item!");

    Debug.WriteLine("Cache Name: " + cacheName);

    Debug.WriteLine("Cache Item Key: " + key);

}

If you want to get notified for other action to the cache, you can use different DataCacheOperations filter. More Info

You can use the bitwise OR to add more filter to your callback event subscription. For example, the following code will raise the OnDataCacheItemChanged callback method if someone add or replace or remove your cache item.

_cache.AddItemLevelCallback(

    "myItem",

    DataCacheOperations.AddItem |

    DataCacheOperations.ReplaceItem |

    DataCacheOperations.RemoveItem,

    OnDataCacheItemChanged);

AppFabric cache notification not just support cache item level notification, it also support for:

• Cache level in bulk
• Cache level
• Item level
• Region level

More Info

Note: These callback events are not supported in Windows Azure Shared Caching.

There are a few more things about AppFabric Caching, but it is too much to cover in one topic. The common and important thing that we need to know about caching such as security, concurrency, expiration and eviction, all can be found in this MSDN article.

Summary

The AppFabric caching is awesome, however, IMHO, if you are needing a simple cache that replace ASP.NET cache, AppFabric caching is overkill. Unless, you really need a caching service that support high availability, scalability, this is what you want.

AppFabric caching is meant to be hosted in different server from your application server. Therefore, hardware and software licensing needs to be considered. Otherwise, you can still choose to ignore the recommendation from Microsoft by hosting the AppFabric cache in the same server with your application server. Then, the server hardware resource could become the concern.

I notice that the AppFabric cache memory consumption is rather high compare to other normal caching facility. By default, the AppFabric caching will utilize 50% of your server memory. And, it is going to reserve quite some amount of memory even though you never have that much of data keeping in the cache or not. However, don't worry, the memory reserve can be tuned down by setting the high / low watermark percentage of memory in the cluster host configuration. See Windows Server AppFabric Memory Consumption Behavior for more info.

If you are looking for smaller caching facility and a replacement for ASP.NET cache for non web application, please come back and check out the next coming blog post.