1. Optimization and Administartion of a Database Management Systems Krystian Zieja

2. Optimizer Modes There are two types of optimizer modes:  Rule based  Cost based

3. Diagnostic Tools STATSPACK Explain Plan SQL Trace and TKPROF SQL*Plus with autotrace feature Oracle SQL Analyze

4. Statspack The following reports on statements are provided by Statspack:  SQL ordered by gets  SQL ordered by reads  SQL ordered by executions  SQL ordered by parse calls

5. Explain Plan Can be used without tracing Needs PLAN_TABLE – use utlxplan.sql script to create it Example: EXPLAIN PLAN FOR SELECT last_name FROM hr.employees;

6. Explain Plan Remember to truncate PLAN_TABLE table before generating next plan You can also use STATEMENT ID Example: EXPLAIN PLAN SET STATEMENT_ID = ‘id’ FOR SELECT ….

7. Explain Plan Query the Plan_Table:  Directly  Using utlxpls.sql  Using utlxplp.sql  Using Dbms_xplan package

8. Task 1 Create PLAN_TABLE in Your schema  Execute utlxplan.sql Describe its structure Explain plans for sample SELECT statements:  EXPLAIN PLAN FOR SELECT * FROM EMP;  EXPLAIN PLAN FOR SELECT ENAME FROM EMP WHERE EMPNO=7896

9. TASK 1Continue EXPLAIN PLAN FOR SELECT * FROM EMP WHERE EMPNO < 7000 Each time query plan table – operation, object name, option select operation, options, object_name, object_type, optimizer from plan_table

10. SQL Trace and TKPROF To set up SQL Trace:  ALTER SESSION SET SQL_TRACE=TRUE  Run your select statements  ALTER SESSION SET SQL_TRACE=FALSE  Format the trace using TKPROF utility  Review the results

11. TKPROF

12. TKPROF statistics:  Count: The number of execution calls  CPU: CPU seconds used  Elapsed: Total elapsed time  Disk: Physical reads  Query: Logical reads for consistent read  Current: Logical reads in current mode  Rows: Rows processed

13. Task 2 Enable Tracing in your user session (ALTER SESSION statement) Issues following statement:  SELECT ename, dname, sal + nvl(comm,0) FROM emp, dept WHERE emp.deptno=dept.deptno;

14. Task 2 Continue Disable tracing in your session Using TKPROF utility prepare a report of your trace file Examine a report

15. SQL*Plus Autotrace Setup Autotrace:  Create Plan_Table  Create and grant plustrace role @ sqlplus\admin\plustrce.sql GRANT plustrace to SCOTT;  Turn on Autotrace SET AUTOTRACE ON  Turn off Autotrace SET AUTOTRACE OFF

16. SQL*Plus Autotrace Autotrace Levels:  ON – SET AUTOTRACE ON  OFF – SET AUTRACE OFF  ON EXPLAIN – SET AUTOTRACE ON EXPLAIN  ON STATISTICS - SET AUTOTRACE ON STATISTICS  TRACEONLY – SET AUTOTRACE TRACEONLY

17. Task 3 Enable autotrace in SQL*Plus and deal with an option presented on previous slide Check following SQL statements SELECT sum(sal), deptno FROM emp Group by deptno Having sum(sal) > 7500

18. Task 3 Continue SELECT ename, sal, grade FROM emp, salgrade Where sal between losal and hisal and deptno in (20,30) SELECT avg(sal),dname FROM emp, dept WHERE emp.deptno = dept.deptno GROUP BY dname