Hi Rajesh,
The mechanism you need is not provided by Lightstreamer kernel and it is requested to the Data Adapter.
The Server receives a single event flow from the Adapter.
This means that the Adapter should take care of sending all the currently active keys (i.e. the snapshot) before sending the EndOfSnapshot signal and, subsequently, the real-time updates.
So, some synchronization is needed and the best case is when the back-end is able to do that.

Otherwise, if you have to ask for snapshot and real-time updates separately, your only option is to hold any real-time updates within the Data Adapter until the snapshot has arrived.
However, by doing this, the Data Adapter should also ensure that real-time updates are really later than the snapshot.
For instance, you should ask the back-end to provide a timestamp for both the snapshot and the real-time update values.
In this way, after forwarding the snaphot to Lightstreamer, you should send only the accumulated real-time updates with a later timestamp.