COMMON DATA VIEW Queries Run In Parallel Even When Parallelism IS Disabled

(Doc ID 2218722.1)

Last updated on JANUARY 29, 2018

Applies to:

Oracle Database - Enterprise Edition - Version 12.1.0.2 and later
Information in this document applies to any platform.

Symptoms

After disabling parallel query, parts of the statement still runs in parallel;

SQL> ALTER SESSION DISABLE PARALLEL QUERY;

Session altered.

SQL> SHOW PDBS


CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
3 PARISQ READ WRITE NO


 EXPLAIN PLAN FOR
Select '',
 t.Owner,
t.Table_Name,
 To_Number(Null),
 '',
 '',
0,
To_Number(Null),
'',
 '',
 Num_Rows,

...

..

UNION-ALL | | | | | | | | | | | |
|*110 | FILTER | | | | | | | | | | | |
| 111 | PX COORDINATOR | | | | | | | | | | | |
| 112 | PX SEND QC (RANDOM) | :TQ20000 | 2 | 686 | | 1 (100)| 00:00:01 | | | Q2,00 | P->S | QC (RAND) |
| 113 | PX PARTITION LIST ALL | | 2 | 686 | | 1 (100)| 00:00:01 | 1 | 2 | Q2,00 | PCWC | |
|*114 | FIXED TABLE FULL | X$COMVW$ | 2 | 686 | | 1 (100)| 00:00:01 | | | Q2,00 | PCWP | |

Queries against Common Data views, such as *_synonyms, *_libraries, etc will still run in parallel.

 

Changes

The database was upgraded to 12C

Cause

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