Remove field in MERG mode

[tvhnet2013]

I want to understand more deeply about LS optimization mechanism in sending MERGE snapshot to client.

If I update null value to 'f3' field, when sending snapshot, does LS send full pairs of <fieldname, value> to client (as your example: f1:value1, f2:value2, f3:null) or just has-value pairs (f1:value1, f2:value2) and ignore null-value field?

[giuseppe.corti]

For a subscription in MERGE mode the snapshot is intended as the list of fields that define the complete state of the item.
In your example if the schema requested by the client is [f1, f2, f3] the values expected for the snapshot are [v1, v2, null] (I confirm you that for internal protocol optimization a null field involves a minimum consumption in size).

The MERGE mode ensures that for each subsequent update that does not involve f3 field the compression algorithm causes that nothing is sent for f3 field (as well as for every other unchanged field).