19. A non-transitory computer-readable storage medium, comprising one or more instructions, which when executed by one or more processors, cause the one or more processors to perform the steps of: creating an index for use by a search engine, wherein the index indexes a set of previously crawled web pages; determining which queries, from a set of queries that have been previously submitted to a search engine, qualify as needy queries; wherein said needy queries are queries for which the index does not currently index adequate, relevant content; estimating an impact, on said needy queries, of fetching a particular uncrawled web page by comparing terms of said needy queries with at least one of: (a) an anchortext of links, obtained from the previously crawled web pages, that point to the particular uncrawled web page, and (b) a Uniform Resource Locator (URL), obtained from the previously crawled web pages, that points to the particular uncrawled web page; ordering web pages to fetch by a web crawler based, at least in part, on the estimated impact, on said needy queries, of crawling the particular uncrawled page.
19. A non-transitory computer-readable storage medium, comprising one or more instructions, which when executed by one or more processors, cause the one or more processors to perform the steps of: creating an index for use by a search engine, wherein the index indexes a set of previously crawled web pages; determining which queries, from a set of queries that have been previously submitted to a search engine, qualify as needy queries; wherein said needy queries are queries for which the index does not currently index adequate, relevant content; estimating an impact, on said needy queries, of fetching a particular uncrawled web page by comparing terms of said needy queries with at least one of: (a) an anchortext of links, obtained from the previously crawled web pages, that point to the particular uncrawled web page, and (b) a Uniform Resource Locator (URL), obtained from the previously crawled web pages, that points to the particular uncrawled web page; ordering web pages to fetch by a web crawler based, at least in part, on the estimated impact, on said needy queries, of crawling the particular uncrawled page. 23. The non-transitory computer-readable storage medium claim 19 , wherein the instructions for comparing terms of said needy queries with at least one of: (a) the anchortext of links, obtained from the previously crawled web pages, that points to the particular uncrawled web page, and (b) the URL, obtained from the previously crawled web pages, that points to the particular uncrawled web page further comprise instructions, which when executed, cause comparing a word-level n-gram representing a query string in a particular needy query and a word-level n-gram representing an anchortext string.