Index having short-term portion and long-term portion

An index of a search engine includes two portions: a long-term portion that is optimized for lookup performance and is stored in bulk storage, for example, non-volatile memory, and a short-term portion that is easily updatable and is stored solely or primarily in random access memory (RAM). Both portions of the index are searchable. The vast majority of documents in the location space are indexed in the long-term portion in a format optimized for lookup, while new documents are immediately searchable in the easily updatable short-term portion, which has a different format. The long-term portion is updated with indexing information of the short-term portion.