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Oracle Tips by Burleson |
OCP Instructors Guide for
Oracle DBA Certification
Chapter 7 - Tuning and Performance
Optimizer Dynamic
Sampling
The values for optimizer_dynamic_sampling range from 0 to 10
with 0 telling the cost-based optimizer to not use dynamic sampling
and the value 10 telling the optimizer to sample all blocks in the
table. The DYNAMIC SAMPLING hint can be used at the statement level
to override the system setting defined by
optimizer_dynamic_sampling.
Oracle recommends that dynamic sampling only be
used when the time required to do the sample is a small fraction of
the statement’s total execution time. It’s a safe assumption that
dynamic sampling will not be used in many OLTP systems but it may
find a home in a few decision support and data warehouse
environments.
The Oracle Database Performance Tuning
(1Z0-033) certification test may have a question on Optimizer Plan
Dynamic Sampling. Test candidates should have a basic understanding
of:
-
The benefits that Optimizer Plan Dynamic
Sampling provides
-
When to use Optimizer Plan Dynamic Sampling
-
How to activate Optimizer Plan Dynamic Sampling
Data Segment Compression
Compressing data has been around since the
inception of the database management system. Data compression
reduces the amount of data being stored, reduces memory usage (more
data per memory block) and increases query performance.
The above text is
an excerpt from:
OCP Instructors Guide for Oracle DBA Certification
A Study Guide to Advanced Oracle Certified Professional Database
Administration Techniques
ISBN 0-9744355-3-8
by Christopher T. Foot
http://www.rampant-books.com/book_2003_2_OCP_print.htm
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