/// <summary>Push a single item onto the queue.</summary>
public void Push(IFdbTransaction tr, T value)
{
Contract.NotNull(tr, nameof(tr));
#if DEBUG
tr.Annotate("Push({0})", value);
#endif
//BUGBUG: can be called multiple times per transaction, so need a unique stamp _per_ transaction!!
tr.SetVersionStampedKey(this.Subspace[tr.CreateUniqueVersionStamp()], this.Encoder.EncodeValue(value));
}