Hi,

This is hard, as you may have multiple procservers spread across multiple servers, so they cannot know if they are the first one without communicating. Some ideas:

A. Let your stage persist its state to a DB, Memcached, Apache Zookeper or similar, to flag whether the first doc has been processed or not
B. Let your feeding logic be the one to know whether it's the first batch of docs or not, and submit a dummy doc which doc which triggers the wanted behavious, before sending the real documents.

It's easier if you first explain exactly why you want this behaviour, often there are other proven ways to achieve same effect.