Every day, millions of users rely on search engines to satisfy the information needs required for performing many routine tasks. The effectiveness and efficiency of a search engine are two prime goals that form a natural trade-off. Meanwhile, search engines continue to rapidly evolve, with larger indexes, more complex retrieval strategies and growing query volumes. Hence, there is a need for efficient query processing infrastructures that make appropriate sacrifices in effectiveness in order to make gains in efficiency. This survey comprehensively reviews the foundations of search...