Gamma uses traditional relational techniques for query parsing, optimization [SELI79, JARK84], and code generation. The optimization process is somewhat simplified as Gamma only employs hash-based algorithms for joins and other complex operations. Queries are compiled into a left-deep tree of operators. At execution time, each operator is executed by one or more operator processes at each participating site. In designing the optimizer for the VAX version of Gamma, the set of possible query plans considered by the optimizer was restricted to only left-deep trees because we felt that there was not enough memory to support right- deep or bushy plans. By using a combination of left-deep.
