How the XgBoost models are aggregated?

Hi,

currently I am mostly interested in models aggregation part of Federated Learning. However, I cannot understand how it is done now. I guess it is used with rabit but cannot find in the code any allreduce function or something and how the global model is upadted. As of now I have a feeling it works likes this:

1) XgBoost model 1 is trained on local data 1 2) XgBoost model 1 is input to model XgBoost model 2 which is trained on local data 2 3) Ends when all local data and temporary XgBoost models are used

It resembles online learning scheme.

Could you help me understand how the aggregation of XgBoost models works here?

mc2-project / federated-xgboost

How the XgBoost models are aggregated? #15