EXPERT RESPONSE
TKPROF, EXPLAIN PLAN, and DBMS_XPLAN all display essentially the same
information. DBMS_XPLAN does have some nice additional information and
it is a good package to use. The big benefit of TKPROF is that you can
trace your session and generate Explain Plans of all your session's SQL
statements, rather then generating them one by one.
To read the output, I go down and right until I can't go down and right
any more. Then cascade back up the tree. For instance:
SELECT STATEMENT
SORT GROUP BY
HASH JOIN
TABLE ACCESS FULL| DEPT |
TABLE ACCESS FULL| EMP |
In the example above, going down and right leads us to a Full Table
Access fo the DEPT table. On that same level, I see another Full Table
Scan of the EMP table. Both of these actions are performed. Going back
up the tree (or to the left, the tree is on its side), I perform a HASH
JOIN of these two tables. I then Sort them and the results are passed
to the SELECT statement.
The following Chapter in the Performance Tuning Guide give much more
information:
http://download-west.oracle.com/docs/cd/B13789_01/server.101/b10752/ex_plan.htm#19259
I'd also read other chapters in that document that pertain to tuning.
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