跨负载平衡服务器的选择性高速缓存清除（ASP.Net）

Question

我们有一个运行在两个负载平衡服务器上的网站。我们使用ASP.Net缓存通过缓存高使用率数据来帮助提高性能。但偶尔数据会发生变化。当它发生时，我们需要清除负载平衡服务器上的相关缓存项目。有没有人有一些容易实施的建议，如何做到这一点？

我知道那里有软件为你管理这个软件（Microsoft Velocity for one）。我也知道还有其他的选择可以分开状态服务器等。但是，对于我们想要的，他们似乎都是过度杀伤性的。现在只需要一个简单的机制来清除跨服务器的特定缓存项目。

感谢您的任何建议。

Answer 1

我们用一个简单的Web服务的方法。我们的缓存清除机制检查web配置设置，以查看是否存在其他服务器，并异步地在这些服务器上调用Web服务。

我们存储具有特定命名召集的数据，以便轻松地清除我们想要的内容。因此，我们传递要删除的项目的前缀或后缀，因为它有时可能是用户特定的（例如，用户标识附加到项目的名称）或特定于应用程序（例如项目的前缀是应用程序名称）。

这里是ClearItem程序，将您节点的任何一个被称为的VB例子：

Public Shared Sub ClearItem(ByVal strPrefix As String, ByVal strPostfix As String) 

    If WebConfig.Caching_Enabled() Then 

     ' Exit if no criteria specified ' 
     If IsNothing(strPrefix) AndAlso IsNothing(strPostfix) Then 
      Exit Sub 
     End If 

     ' At the very least we need a Postfix ' 
     If Not IsNothing(strPostfix) AndAlso Not strPostfix.Length.Equals(0) Then 
      _ClearItem(strPrefix, strPostfix) 
     End If 

     If WebConfig.Caching_WebFarmEnabled() Then 
      ' Now clear the cache across the rest of the server farm ' 
      _ClearItem_WebFarm(strPrefix, strPostfix) 
     End If 

    End If 

End Sub 

Private Shared Sub _ClearItem_WebFarm(ByVal strPrefix As String, ByVal strPostfix As String) 

    If WebConfig.Caching_WebFarmEnabled() Then 

     ' Use a web service on each server in the farm to clear the ' 
     ' requested item from the Cache ' 

     ' Determine which servers need to remove cache items ' 
     Dim arrServers As String() 
     arrServers = Split(WebConfig.Caching_WebFarmServers(), "|") 

     Dim strServer As String ' Holds which server we are currently contacting ' 

     ' Loop through all the servers and call their web services ' 
     For Each strServer In arrServers 

      Dim WS As New WebServiceAsyncCall 
      WS.StartCallBack(strServer, strPrefix, strPostfix) 

     Next 

    End If 

End Sub 

Private Shared Sub _ClearItem(ByVal strPrefix As String, ByVal strPostfix As String) 

    If WebConfig.Caching_Enabled() Then 

     ' Determine how we are comparing keys ' 
     Dim blnPrefix, blnPostfix As Boolean 

     If strPrefix.Length.Equals(0) Then 
      blnPrefix = False 
     Else 
      blnPrefix = True 
     End If 

     If strPostfix.Length.Equals(0) Then 
      blnPostfix = False 
     Else 
      blnPostfix = True 
     End If 

     ' Reference the Cache collection ' 
     Dim objCache As System.Web.Caching.Cache = HttpContext.Current.Cache 

     ' Exit if the cache is empty ' 
     If objCache.Count.Equals(0) Then 
      Exit Sub 
     End If 

     ' Clear out the cache for all items matching the input(s) (on this local server) ' 
     Dim objCacheEnum As IEnumerator = objCache.GetEnumerator() 
     Dim objCacheItem As Object 
     Dim objCurrentKey As System.Collections.DictionaryEntry 
     Dim strCurrentKey As String 

     ' Enumerate through the cache ' 
     While objCacheEnum.MoveNext() 

      objCurrentKey = CType(objCacheEnum.Current, DictionaryEntry) 
      strCurrentKey = objCurrentKey.Key.ToString() 

      ' How are we comparing the key? ' 
      If blnPrefix AndAlso Not (blnPostfix) Then ' Only by PREFIX ' 

       If strCurrentKey.StartsWith(strPrefix) Then 
        ' Remove it from the cache ' 
        objCacheItem = objCache.Remove(strCurrentKey) ' Returns a reference to the item ' 
        objCacheItem = Nothing ' Need to explicitly nuke this because the objCache.Remove() above doesn t destroy ' 
       End If 

      ElseIf Not (blnPrefix) AndAlso blnPostfix Then ' Only by POSTFIX ' 

       If strCurrentKey.EndsWith(strPostfix) Then 
        ' Remove it from the cache ' 
        objCacheItem = objCache.Remove(strCurrentKey) ' Returns a reference to the item ' 
        objCacheItem = Nothing ' Need to explicitly nuke this because the objCache.Remove() above doesn t destroy ' 
       End If 

      ElseIf blnPrefix AndAlso blnPostfix Then ' By both PREFIX and POSTFIX' 

       If strCurrentKey.StartsWith(strPrefix) AndAlso strCurrentKey.EndsWith(strPostfix) Then 
        ' Remove it from the cache ' 
        objCacheItem = objCache.Remove(strCurrentKey) ' Returns a reference to the item ' 
        objCacheItem = Nothing ' Need to explicitly nuke this because the objCache.Remove() above doesn t destroy ' 
       End If 

      Else 
       ' Not comparing prefix OR postfix? Why bother continuing then! ' 
       Exit Sub 
      End If 

     End While 

    End If 

End Sub 

你可以看到，上面的代码中使用这个辅助类调用其他的服务器（S）：

Private Class WebServiceAsyncCall 

    Public Sub StartCallBack(ByVal strService As String, ByVal strPrefix As String, ByVal strPostfix As String) 

     ActiveWebServiceCounter += 1 

     Dim clearCacheProxy As New CacheClearService.CacheClear ' This is the web service which of course will exist on the other node as well ' 
     clearCacheProxy.Url = strService 

     AddHandler clearCacheProxy.ClearItemCompleted, AddressOf DoneCallBack 

     clearCacheProxy.ClearItemAsync(strPrefix, strPostfix) 

    End Sub 

    Public Sub DoneCallBack(ByVal sender As Object, ByVal e As CacheClearService.ClearItemCompletedEventArgs) 

     ActiveWebServiceCounter -= 1 

     If e.Result.Length > 0 Then ' Something failed ' 
      ' Log the error ' 
     End If 

    End Sub 

End Class 

远程服务器上的Web服务然后调用与_ClearItem调用的代码相同的代码。

Answer 2

为什么不在两个服务器都可以看到的对象上定义Cache Dependancy？您可以使用SQL或File缓存依赖性。

Link to Caching Msdn Page