My Sqlcache Doesn't Work Consistently Under ASP.NET 2.0, Any Suggestion?

I have some problem with ASP.NET cache, I found other people has similar problem, but I didn't find real solution.

The one bother me most is the SQLCacheDependency doesn't work stable. I insert object in cache and has SQLCacheDependency linked. After a period of time, it stopped working. That means the the object is still in cache, but change on db side doesn't remove the cache entry. I am not sure if it is ASP side or SQL side, I feel it is ASP side.

I am using 2.0 + SQL 2005.

Once the db command notification stop working, you have to restart IIS or clear all items in cache since you don't kno which one is changed.

The following is the code I use to handle the cache :

string cacheKey = LinkSites.GetMappedKey(virtualPath, fileid.ToString()); // this will return a key from virtualPath
if (!String.IsNullOrEmpty(cacheKey)) frd = (FileRecordData)HttpContext.Current.Cache[cacheKey];
if (frd == null)
{
int siteid = 0;
SqlCacheDependency scd = null;
lock (_connection)
{
try
{
SqlCommand sqlcmd = new SqlCommand("select ownerid,id,uniqueid,parentid,category,name,content,dated=isnull(updated,created),created,updated,isdirectory from dbo.link_sourcestore where id=@id", Connection);
sqlcmd.CommandType = CommandType.Text;
SqlParameter sqlparam;
sqlparam = sqlcmd.Parameters.Add("@id", SqlDbType.Int);
sqlparam.Value = fileid;

scd = new SqlCacheDependency(sqlcmd);
using (SqlDataReader reader = sqlcmd.ExecuteReader())
{
if (!reader.HasRows) return null;
reader.Read();
siteid = LinkRoutine.Convert(reader["ownerid"], 0);
frd = GetRecordData(reader);
}
}
catch (Exception e)
{
ErrorHandler.Report("GetCachedFileRecord 2 [" + realVirtualPath + "," + virtualPath + "]", e);
return null;
}
}

if (scd != null)

{
frd.CacheKey = cacheKey;
frd.CacheDependency = scd;
HttpRuntime.Cache.Insert(cacheKey, frd, scd, Cache.NoAbsoluteExpiration, new TimeSpan(24, 0, 0), CacheItemPriority.NotRemovable, new CacheItemRemovedCallback(LinkCacheHandler.RemovedCallback));
}
}

It just read the record and add into cache, when cache item removed, call the static method RemovedCallback in LinkCacheHandler, LinkCacheHandler is posted below. After I restart IIS, it will work for a while, 5, 10 or more minutes, but after a while, even I set breakpoint in RemovedCallback, I don't get anything when I change the record. (when I call my clear cache method, which will remove all records from cache, it runs to the breakpoint. So the callback is fine)

public class LinkCacheHandler
{
public static void RemovedCallback(string k, object v, CacheItemRemovedReason r)
{
if (!k.Contains("system/cache.ascx"))
{
LinkSites._cacheLog += "RemovedCallback[" + DateTime.Now.ToString() + "]<br/> " + k + ((v is FileRecordData)?(" : " + ((FileRecordData)v).CacheKey) : "") + " " + r.ToString() + "
<br/>";
LinkSites.NotifyCacheObject(k);
}
}
}