> For example, the planner may be able to > more easily recognise a statement and reuse an existing plan rather than > re-planning the query. This is a double edged sword. Reuse an existing plan can be bad in those cases where the data distribution is not suitable for the current plan. This has been the achilles heel of many RDBMS. Only in Oracle 12c there are options to let the planner change existing plan by peeking into the parameter values (supplied in ? of prepare) and checking it against the distribution.
