17. A non-transitory computer readable storage medium storing one or more sequences of instructions executable by one or more processors to perform a set of operations comprising: training a first ranking function that uses online data computed at a time of receiving a search request and stored in an index to produce a first ranking score for an item among a plurality of items, the online data includes a set of search results including at least information about a product; training a second ranking function to produce a second ranking score for the item, the second ranking function trained using a boost method, the second ranking function using offline data unavailable in the index in combination with the first ranking score produced by the first ranking function; and ranking the item among a plurality of items based at least in part on both the first ranking score and the second ranking score, the item is the product in a database of products accessible on a network, wherein ranking the item is performed to determine a relevance of the item among the search results in a context of the search request.
19. The non-transitory computer readable storage medium of claim 17 , wherein the boosting method is a gradient boosting method.