APPLIES TO:

PURPOSE

 This document is to explain the behavior of AutoDOP with respect to PARALLEL_DEGREE_POLICY and PARALLEL Hint.

DETAILS

"Oracle Database Reference 11.2" defines PARALLEL_DEGREE_POLICY as:

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Specifies whether or not automatic degree of Parallelism, statement queuing, and in-memory parallel execution will be enabled.

If PARALLEL_DEGREE_POLICY=MANUAL
Disables automatic degree of parallelism, statement queuing, and in-memory parallel execution.
This reverts the behavior of parallel execution to what it was prior to Oracle Database 11g Release 2 (11.2). This is the default.
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But from the bug# 15906881 it is known that AutoDOP will also be enabled if the SQL uses any PARALLEL hint.
So Users are expected to see AutoDOP used for the Query although PARALLEL_DEGREE_POLICY is set to MANUAL.

>>>
alter session set events 'trace[SQL_Compiler.*] disk=highest';
run your query
alter session set events 'trace[SQL_Compiler.*] off';
<<<

The above trace will produce a trace file in which the following line is displayed which actually confirms this behavior.
"Automatic degree of parallelism is enabled for this statement in hint mode"

A Doc Bug# 16571853 is filed to correct the Documentation.

Note:
AutoDOP still needs I/O Calibration Statistics.
If no I/O Calibration Statistics exists then AutoDOP will automatically be disabled though the PARALLEL hint enables it.

You can see below line in trace file:
"Automatic degree of parallelism is disabled: IO calibrate statistics are missing."