Oracle Hints

Question:  What are Oracle hints, and how do I use them?

Answer:  An Oracle hint is an optimizer directive that is embedded into an SQL statement to suggest to Oracle how the statement should be executed.  For example, here is an Oracle hint to change the default optimizer mode for a query:

Select /*+first_rows_10*/
 mycol,
from
 mytab;

You can follow these steps for tuning your Oracle hints and then reverse engineer the regular SQL statements to emulate the execution plan generated by the hints is one of many ways to use Oracle hints.  Using Oracle hints can be extremely complicated, which is why Oracle hints are considered to be a last resort measure as a means to change your SQL execution plan (after changing CBO statistics, instance parameters, etc.).  There is a large number of Oracle hints for use in optimizing your SQL, and some hints are not documented at all. 

Here are some related notes on Oracle hints:

• Oracle SQL Hints Tuning

• Oracle SQL undocumented tuning hints

• Oracle tuning steps: SQL statements

• Oracle hints tips

• Oracle leading vs. ordered hints

• Using result cache hints

• Oracle SQL tuning with hints

• Oracle 10g hint list

• Oracle good hints list

• Oracle index hint syntax

• Oracle 10g SQL tuning with hints

• Oracle SQL ignored hint

• Optimizer hints in Oracle 11g and hint overkill
  

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