Hi,
First of all, just to be sure, I assumed we are talking about a DISTINCT subscription type, am I right?
In Lightstreamer there is not such a feature already built in, but you can maybe implement it relatively easily on top of Lightstreamer, using selectors.
The Item should have a counter field, which holds a sequence number incremented for each ItemEvent.
The idea is to subscribe an item specifying a selector. A selector is a string, representing a name or a predicate, which will be used by the Metadata Adapter to determine if an ItemEvent should be filtered. In this case the selector should bear the latest sequence number received by the client: something like "SequenceNum=213258".
You have to implement the 'isSelected' method in your MetadataProvider, where you compare the sequence number of the ItemEvent whit the seq num of the selector, to determine if the item was already sent to the client and in case avoid to send it again.
By the way you have to be aware that the 'isSelected' method is called for every itemEvent entering the ItemEventBuffer, before being sent to the client, and not just the ItemEnets of the snapshot, therefore the 'isSelected' method should perform fast, and must be implemented carefully, to avoid to slow down the whole update delivery process.
You may find more details in section 3.3.1 of
General Concepts , in the description of method
setSelector of
Lightstreamer JavaScript Client 6.0.1 API and the method 'isSelected' of the MetadataProvider interface in '
Java Adapter API Reference '
hth,
Marco
