17. The non-transitory storage medium of claim 15 , wherein optimizing the search result ranking algorithm using the relevance label of each query-document pair of the first set generated by the optimized target function includes optimizing the search result ranking algorithm using the relevance label of each query-document pair of a second set of query-document pairs generated by the optimized target function.
15. A tangible non-transitory computer readable storage medium storing instructions for optimizing search result rankings obtained from a search result ranker, the search result ranker executing a search result ranking algorithm, the instructions, when executed by a computer, cause the computer to perform operations comprising: retrieving a first set of query-document pairs, each query-document pair of the first set having an associated post-impression features vector representative of a number of post-impression features associated with a document of the query-document pair; generating an original weight vector having a number of originally-assigned weights corresponding to the number of post-impression features in each of the post-impression features vector of the first set; generating a target function by using the weight vector and the post-impression features vectors of the first set, the original weight vector having the number of originally-assigned weights of the first set; using a performance metric associated with the search ranking algorithm, optimizing the originally-assigned weights of the weight vector using the first set of query-document pairs to obtain an optimized target function, the optimized target function including a number of optimized weights, the optimized weights of the optimized target function representative of an impact of each post-impression feature of the post-impression features vector to a determination of a relevance of the document, the optimizing being executed such that the performance metric of the search ranking algorithm is maximized; optimizing the search result ranking algorithm using a relevance label of each query-document pair of the first set generated by the optimized target function; and using the optimized search result ranking algorithm to rank search results.