Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
Solved

# cbo optimer

Posted on 2013-01-07
Medium Priority
235 Views
In a simple way what is the meaning of cost base optimizer..
0
Question by:walkerdba
[X]
###### Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

• Help others & share knowledge
• Earn cash & points

LVL 77

Expert Comment

ID: 38753243
It is code that uses statistics to choose the best execution plan for whatever the task is.

The old way was rule based.  It had strict rules to follow.  For example, if an index exists, use it no matter what.

The problem here is at times using an index will actually slow down the execution.

See if this helps fill in the gaps:
http://www.dba-oracle.com/art_otn_cbo.htm
0

LVL 23

Expert Comment

ID: 38753368
Hi walker, for every statement, the Oracle system will attempt to optimize the execution cost.  As slight mentioned, statistics provide the metadata used to evaluate the size and distribution of data.

Is that simple enough? <grins>
0

LVL 38

Accepted Solution

Geert Gruwez earned 2000 total points
ID: 38753711
it's all in the words
optimize the work based on the cost
the work is the exection of a query following a certain plan
every step in the plan has a certain cost
the best plan usually has the lowest cost

your next question could be what is a hard parse ...
hard parse is working out that execution plan
0

LVL 8

Expert Comment

ID: 38756172
Let me see if i can provide any inputs here.

In a simple way what is the meaning of cost base optimizer..
=> when we go to a market to buy something, we choose a product of low cost(ofcourse, not compromising on the quality).
=> Similarly, Oracle calculates the cost(for each unit of operation viz. performing a full table scan/index unique scan/range scan etc., )and gives us each step in the execution plan and the the cost associated with it.

Just my 2 cents.
0

Author Closing Comment

ID: 38765207
yes
0

## Featured Post

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Have you ever had to make fundamental changes to a table in Oracle, but haven't been able to get any downtime?  I'm talking things like: * Dropping columns * Shrinking allocated space * Removing chained blocks and restoring the PCTFREE * Re-or…
How to Unravel a Tricky Query Introduction If you browse through the Oracle zones or any of the other database-related zones you'll come across some complicated solutions and sometimes you'll just have to wonder how anyone came up with them.  …
This video shows, step by step, how to configure Oracle Heterogeneous Services via the Generic Gateway Agent in order to make a connection from an Oracle session and access a remote SQL Server database table.
This video shows how to copy a database user from one database to another user DBMS_METADATA.  It also shows how to copy a user's permissions and discusses password hash differences between Oracle 10g and 11g.
###### Suggested Courses
Course of the Month6 days, 1 hour left to enroll