Question: Oracle 11g release 2 has
introduced a new parallel parameter called
parallel_degree_policy. Is parallel_degree_policy
like the parallel_automatic_tuning parameter?
Answer: The parallel_degree_policy
parameter is the successor to the deprecated
parallel_automatic_tuning parameter, a
parameter with significant issues. The parallel_degree_policy is
indeed a replacement for PAT that is designed for use exclusively in
data warehouse and decision support environments. (Automatic
parallelism is not recommended for OLTP databases or systems with
first_rows_n optimization).
- New "augmented" Buffering:
With parallel_degree_policy=auto Oracle can
use their new augmented data buffer method dubbed "in-memory
parallel execution" for partitioned table scans. This is a
replacement to the PGA-based buffering that was used in parallel
large-table full-table scans in non-RAC systems to keep the
standard SGA data buffer pool from being overwhelmed since only
objects that consume less than 2% of the db_cache_size
or db_nnk_cache_size would use the regular SGA buffer.
- Automatic parallelism and degree: Setting
parallel_degree_policy=auto allows Oracle to decide how
much parallelism (if any) to use on a SQL query. Most
shops will hardcode their degree of parallelism based on their
own experience with job throughput, a more accurate approach
than using any automated soilution.
- SQL queuing: Setting
parallel_degree_policy=auto also enabled parallel query
queuing, a feature whereby a SQL is delayed when running it
would saturate the I/O subsystem. This is useful for
nighttime batch processing, but its not appropriate for any jobs
where minimizing response time is a primary goal. Most
shops use dbms_scheduler to single-thread or
parallelize their job manually, in most cases a better approach
than an automated solution.
|
|
 |
|
Guarantee your Success!
Oracle is the
world's most complex, robust and flexible database, considered
impossible to master without a mentor.
That's why all BC
Oracle trainers are working professionals, experts in Oracle who
share their tips and secrets. |
|
| |
|
Burleson is the American Team
Note:
This Oracle
documentation was created as a support and Oracle training reference for use by our
DBA performance tuning consulting professionals.
Feel free to ask questions on our
Oracle forum.
Verify
experience!
Anyone
considering using the services of an Oracle support expert should
independently investigate their credentials and experience, and not rely on
advertisements and self-proclaimed expertise. All legitimate Oracle experts
publish
their Oracle
qualifications.
Errata?
Oracle technology is changing and we
strive to update our BC Oracle support information. If you find an error
or have a suggestion for improving our content, we would appreciate your
feedback. Just
e-mail:
 and include the URL for the page.
Copyright ? 1996 - 2012
All rights reserved.
Oracle ?
is the registered trademark of Oracle Corporation.
|
|
