1. A computer-implemented method for online learning of click-through rates on federated result blocks from one or more federated sources, comprising: receiving, by a computer, click-through feedback for the federated result blocks from the one or more federated sources in response to a query; assigning, by the computer, a weight to each of the federated result blocks based on the received click-through feedback; ranking, by the computer, the federated result blocks based on the assigned weights; and generating, by the computer, a search results page for displaying the ranked federated result blocks, the ranked federated result blocks being displayed in one of a plurality of hierarchical slots based on a predetermined threshold value.