I'm using NHibernate with Velocity as a 2nd cache level provider.

I need to clear a region. I'm using this code:

_sessionFactory.EvictQueries("Authorization");
var authCache = _sessionFactory.GetSecondLevelCacheRegion("Authorization");
authCache.Clear();

authCache.Clear() is actually calling NHibernate.Caches.Velocity.VelocityClient.Cache method.

The region is cleared correctly. But right after that, there's a new session opened and a query is made against an entity which was previously cached. It tries to GetAndLock in VelocityClient. Bang. The AppFabricCachingService crashes (see event log below)

Am I clearing the cache correctly? What's my mistake?

=====================

EVENT LOG

AppFabric Caching service crashed with exception {System.Runtime.CallbackException: Async Callback threw an exception. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.ApplicationServer.Caching.MultiDirectoryHashtable.GetPlaceHolderObject(Object key)
   at Microsoft.ApplicationServer.Caching.MultiDirectoryHashtable.PreProcess(MDHObjectNode oldObjectNode, MDHObjectNode& newObjectNode, MDHOperationInfo& operationInfo)
   at Microsoft.ApplicationServer.Caching.MultiDirectoryHashtable.PutNodeInSlot(MDHOperationInfo& operationInfo, MDHDirectoryNode dir, Int32 slotIndex)
   at Microsoft.ApplicationServer.Caching.MultiDirectoryHashtable.TryOperation(MDHOperationInfo& operationInfo)
   at Microsoft.ApplicationServer.Caching.MultiDirectoryHashtable.PerformOperation(MDHOperationInfo& operationInfo)
   at Microsoft.ApplicationServer.Caching.MultiDirectoryHashtable.GetAndLock(Object key, TimeSpan lockTimeOut, Boolean lockKey, DMOperationCallBack preOperation, DMOperationCallBack postOperation, Object opState)
   at Microsoft.ApplicationServer.Caching.DMHashContainer.GetAndLock(Object key, TimeSpan lockTimeOut, Boolean lockKey, Object opState)
   at Microsoft.ApplicationServer.Caching.ObjectManager.GetAndLock(String cacheName, String regionName, Object key, TimeSpan lockTimeOut, DataCacheLockHandle& lHandle, Boolean lockKey, Object opState)
   at Microsoft.ApplicationServer.Caching.VelocityDataStore.ProcessWriteRequest(RequestBody request)
   at Microsoft.ApplicationServer.Caching.VelocityDataStore.ProcessMessageRequest(RequestBody request)
   at Microsoft.ApplicationServer.Caching.DistributedObjectManager.OnReceiveMessageFromRemoteDRM(IReplyContext replyContext)
   at Microsoft.ApplicationServer.Caching.WcfTransportChannel.InvokeCallback(Message message, IChannelContainer container)
   at Microsoft.ApplicationServer.Caching.WcfServerChannel.InvokeCallback(Message message, IChannelContainer container)
   at Microsoft.ApplicationServer.Caching.WcfServerChannel.CompleteProcessing(IAsyncResult result)
   at Microsoft.ApplicationServer.Caching.WcfTransportChannel.Receive(IAsyncResult result)
   at System.Runtime.AsyncResult.Complete(Boolean completedSynchronously)
   --- End of inner exception stack trace ---
   at System.Runtime.AsyncResult.Complete(Boolean completedSynchronously)
   at System.Runtime.AsyncResult.Complete(Boolean completedSynchronously, Exception exception)
   at System.ServiceModel.Channels.SynchronizedMessageSource.ReceiveAsyncResult.OnReceiveComplete(Object state)
   at System.ServiceModel.Channels.SessionConnectionReader.OnAsyncReadComplete(Object state)
   at System.ServiceModel.Channels.StreamConnection.OnRead(IAsyncResult result)
   at System.Runtime.Fx.AsyncThunk.UnhandledExceptionFrame(IAsyncResult result)
   at System.Net.LazyAsyncResult.Complete(IntPtr userToken)
   at System.Net.LazyAsyncResult.ProtectedInvokeCallback(Object result, IntPtr userToken)
   at System.Net.Security.NegotiateStream.ProcessFrameBody(Int32 readBytes, Byte[] buffer, Int32 offset, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.NegotiateStream.ReadCallback(AsyncProtocolRequest asyncRequest)
   at System.Net.AsyncProtocolRequest.CompleteRequest(Int32 result)
   at System.Net.FixedSizeReader.CheckCompletionBeforeNextRead(Int32 bytes)
   at System.Net.FixedSizeReader.ReadCallback(IAsyncResult transportResult)
   at System.Runtime.AsyncResult.Complete(Boolean completedSynchronously)
   at System.Runtime.AsyncResult.Complete(Boolean completedSynchronously, Exception exception)
   at System.ServiceModel.Channels.ConnectionStream.ReadAsyncResult.OnAsyncReadComplete(Object state)
   at System.ServiceModel.Channels.SocketConnection.FinishRead()
   at System.ServiceModel.Channels.SocketConnection.AsyncReadCallback(Boolean haveResult, Int32 error, Int32 bytesRead)
   at System.ServiceModel.Channels.OverlappedContext.CompleteCallback(UInt32 error, UInt32 numBytes, NativeOverlapped* nativeOverlapped)
   at System.Runtime.Fx.IOCompletionThunk.Un开发者_高级运维handledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped)
   at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP)}. Check debug log for more information

It's a know AF Cache bug. Region Clear is leads to crash when there are locked cache items. See this thread:

Exception when clearing system regions

The workaround is: instead of clear you should do a cluster restart in the included AF Cache PS console.