Although optimized query plans generally outperform adjusted query plans, the difference in performance is not always significant. The ultimate effect on performance depends on the number of worker processes that Adaptive Server uses in the adjusted plan, and whether or not a serial access method is used in place of a parallel method. Obviously, the most negative impact on performance occurs when Adaptive Server uses a serial access method instead of a parallel access method to execute a query.
The performance of multitable join queries can also suffer dramatically from adjusted query plans, since Adaptive Server does not change the join ordering when creating an adjusted query plan. If an adjusted query plan is executed in serial, the query can potentially perform more slowly than an optimized serial join. This may occur because the optimized parallel join order for a query is different from the optimized serial join order.
