What SQL optimization does Virtuoso perform?
Virtuoso has a cost-based SQL optimizer. It uses table row count, data size and value distribution statistics for evaluating the cost of diverse execution plans. For each plan, loop invariants are extracted, loop and hash join types are evaluated, different indices are compared for access performance and predicates are evaluated as early as possible, most restrictive first, for any join order being contemplated. Additionally, the programmer can explicitly specify the join order and join type (loop/hash) for each table.
