Extending RDBMS technology to achieve performance and scalability for queries that are much more powerful than those of SQL-2 has been the goal of deductive database research for more than thirty years. The e system has made major progress toward this goal, by (1) Datalog extensions that support the more powerful recursive queries needed in advanced applications, and (2) superior performance for both traditional recursive queries and those made possible by the new extensions, while (3) delivering competitive performance with commercial RDBMSs on non-recursive queries. In this paper, we focus on the techniques used to support the in-memory evaluation of Datalog programs on multicore machines. In e, a Datalog program is represented as an AND/OR tree, and multiple copies of the same AND/OR tree are used to access the tables in the database concurrently during the parallel evaluation. We describe compilation techniques that (1) recognize when the given program is lock-free, (2) transform a locking program into a lock-free program, and (3) find an efficient parallel plan that correctly evaluates the program while minimizing the use of locks and other overhead required for parallel evaluation. Extensive experiments demonstrate the effectiveness of the proposed techniques.