public void Add (MemoryCacheEntry entry)
{
var now = DateTime.UtcNow;
if (now == prevDateTime)
dateTimeIndex++;
else
dateTimeIndex = 0;
prevDateTime = now;
entry.UtcLastUpdateUsage = now;
entry.UsageEntryRef = new UsageEntryRef ();
entry.UsageEntryRef.DateTimeIndex = dateTimeIndex;
base.Add (entry);
}