# Optimizer Hints¶

We have already mentioned the GATHER_PLAN_STATISTICS hint, which can be used to obtain statistics about the execution plan during the execution of a statement. It is especially helpful when you intend to diagnose performance issues with a particular statement. It is definitely not meant to be used in production instances!

There is also a GATHER_OPTIMIZER_STATISTICS, which Oracle lists under ‘Other hints’. It can be used to collect bulk-load statistics for CTAS statements and INSERT INTO ... SELECT statements that use a direct-path insert, which is accomplished with the APPEND hint, but more on that later. The opposite, NO_GATHER_OPTIMIZER_STATISTICS is also provided.

The OPTIMIZER_FEATURES_ENABLE hint can be used to temporarily disable certain (newer) optimizer feature after database upgrades. This hint is typically employed as a short-term solution when a small subset of queries performs badly. Valid parameter values are listed in the official documentation.