oracle 当查询比较慢的时候,可以考虑并发查询,可以很快出结果,预计比之前不加快2-4倍。
Parallel Query Intra- and Inter-Operation Example As an example of parallel query with intra- and inter-operation parallelism,consider a more complex query: SELECT /*+ PARALLEL(employees 4) PARALLEL(departments 4) USE_HASH(employees) ORDERED */ MAX(salary),AVG(salary) FROM employees,departments WHERE employees.department_id = departments.department_id GROUP BY employees.department_id;
http://docs.oracle.com/cd/B10500_01/server.920/a96524/c20paral.htm