SELECTING DATA COLLECTIONS TO SEARCH BASED ON THE QUERY

Methods, systems, and apparatus, including computer programs encoded on computer storage media, for receiving a new query that is not in a query cache, the new query including one or more query terms; determining that the new query is a variant of a cached query in the query cache; in response to determining that the new query is a variant of the cached query, obtaining a first probability, the first probability indicating a likelihood that a collection of resources includes resources that satisfy the cached query; calculating a second probability, the second probability being a probability that the one or more query terms in the new query name an entity or are a phrase; calculating a third probability, the third probability being a probability that the cached query is a specific query; and determining, based on the first, second, and third probabilities, whether to search the collection of resources.