5. A computer implemented method, comprising: under the control of one or more computer systems configured with executable instructions, 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.
10. The computer implemented method of claim 5 , wherein the first ranking score is computed and stored into the index periodically upon expiration of a predetermined time interval.