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Oracle Tips by Burleson |
OCP Instructors Guide for
Oracle DBA Certification
Chapter 7 - Tuning and Performance
Using Explain Plan to
Determine Access Paths
2.1 NESTED LOOPS
3.1 NESTED LOOPS
4.1 TABLE ACCESS FULL
PUBLISHER_REP_FIRM
4.2 TABLE ACCESS BY
ROWID APPROVAL_STATUS
5.1 INDEX
UNIQUE SCAN
PK_APPROVAL_STATUS UNIQUE
3.2 TABLE ACCESS BY ROWID
PUBLISHER_APP
4.1 INDEX UNIQUE SCAN
PK_PUBLISHER_APP UNIQUE
It is easier to understand the access path if
you take the output and draw or graph the access path’s steps (refer
to figure 10). The statement above would produce the following
graphical access path display:
Figure 10: Access path steps.
Let's take a few moments to review the above
access path. Although you draw the operations from the top down and
left to right, Oracle will execute the operations from the left to
right and then bottom to top:
-
Operation 4.1 – Oracle is performing a full table scan on the
outer-table
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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