1. One or more processor-accessible tangible media comprising processor-executable instructions for combining rankers to perform a search operation, wherein the processor-executable instructions, when executed, direct a system to perform acts comprising: ascertaining a count of a number of instances that a respective query-identifier pair from among multiple query-identifier pair entries corresponding to a query is recorded in log data, the count of the number of instances of the respective query-identifier pair reflecting a number of user interactions with the respective query-identifier pair that are associated with previous submissions of the query by users; performing a search for the query to produce a set of search results; and ranking the set of search results by relevance score by combining scores from a document-based ranker and a log-based ranker into a combined score using a weighting factor that is adapted as a function of the count of the number of instances of the respective query-identifier pair corresponding to the query recorded in the log data such that a relative contribution of the document-based ranker to the combined score decreases as the count of the number of instances of the respective query-identifier pair in the log data increases.