My Oracle Support Banner

Parallel Hint Ignored With Large Number Of Columns In Select List (Doc ID 1267953.1)

Last updated on FEBRUARY 19, 2019

Applies to:

Oracle Database - Enterprise Edition - Version 10.2.0.1 to 10.2.0.4 [Release 10.2]
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Backup Service - Version N/A and later
Information in this document applies to any platform.
Reviewed 11-Dec-2014.

Symptoms

The parallel hint ignores with large numbers of columns in select list, for example:

select /*+ parallel ("DUAL",4) */
1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
[...]
[...] <--- Y same row
from dual
where dummy='X'
union
select /*+ parallel ("DUAL",4) */
1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
[...]
[...] <--- Y same row
from dual
where dummy='X'
/

with Y=1000 it works
with Y=2000 it does not use parallelism

Basically, using about 2000 rows, then the parallelism doesn't work.

Using 1000 rows:

Cause

To view full details, sign in with your My Oracle Support account.

Don't have a My Oracle Support account? Click to get started!


In this Document
Symptoms
Cause
Solution
References


My Oracle Support provides customers with access to over a million knowledge articles and a vibrant support community of peers and Oracle experts.