Search logs, which contain rich and up-to-date information about users' needs and preferences, have become a critical data source for search engines. Recently, more and more data-driven applications are being developed in search engines based on search logs, such as query suggestion, keyword bidding, and dissatisfactory query analysis. In this paper, by observing that many data-driven applications in search engines highly rely on online mining of search logs, we develop an OLAP system on search logs which serves as an infrastructure supporting various data-driven applications. An empirical study using real data of over two billion query sessions demonstrates the usefulness and feasibility of our design. Categories and Subject Descriptors H.2.8 [Database Management]: Database Applications-Data Mining General Terms Algorithms, Experimentation Keywords OLAP, search log, query session, suffix tree